Patent Publication Number: US-2023157886-A1

Title: Non-invasive and minimally invasive laser surgery for the reduction of intraocular pressure in the eye

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 17/019,013, filed Sep. 11, 2020, for “Non-Invasive and Minimally Invasive Laser Surgery for the Reduction of Intraocular Pressure in the Eye,” which is a divisional application of U.S. patent application Ser. No. 16/125,588, filed Sep. 7, 2018, now U.S. Pat. No. 11,110,006, for “Non-Invasive and Minimally Invasive Laser Surgery for the Reduction of Intraocular Pressure in the Eye,” the entire disclosures of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to the field of medical devices and treatment of diseases in ophthalmology, and more particularly to systems, apparatuses, and methods for non-invasive and minimally invasive treatment of tissues, especially ocular tissue structures in the irido-corneal angle of the eye, for the laser surgery treatment of glaucoma. 
     BACKGROUND 
     Before describing the different types of glaucoma and current diagnosis and treatments options, a brief overview of the anatomy of the eye is provided. 
     Anatomy of the Eye 
     With reference to  FIGS.  1 - 3   , the outer tissue layer of the eye  1  includes a sclera  2  that provides the structure of the eye&#39;s shape. In front of the sclera  2  is a cornea  3  that is comprised of transparent layers of tissue that allow light to enter the interior of the eye. Inside the eye  1  is a crystalline lens  4  that is connected to the eye by fiber zonules  5 , which are connected to the ciliary body  6 . Between the crystalline lens  4  and the cornea  3  is an anterior chamber  7  that contains a flowing clear liquid called aqueous humor  8 . Encircling the perimeter of the crystalline lens  4  is an iris  9  which forms a pupil around the approximate center of the crystalline lens. A posterior chamber  10  is located between the crystalline lens  4  and the retina  11 . Light entering through the cornea  3  is optically focused through the crystalline lens  4 . 
     With reference to  FIG.  2   , the corneoscleral junction of the eye is the portion of the anterior chamber  7  at the intersection of the iris  9  and the sclera  2 . The anatomy of the eye  1  at the corneoscleral junction includes a trabecular meshwork  12 . The trabecular meshwork  12  is a fibrous network of tissue that encircles the iris  9  within the eye  1 . The base of the trabecular meshwork  12  and the edge of the iris  9  are attached together at the scleral spur  14 . The network of tissue layers that make up the trabecular meshwork  12  are porous and thus present a pathway for the egress of aqueous humor  8  flowing from the anterior chamber  7 . This pathway may be referred to herein as an aqueous humor outflow pathway, an aqueous outflow pathway, or simply an outflow pathway 
     Referring to  FIG.  3   , the pathway formed by the pores in the trabecular meshwork  12  connect to a set of thin porous tissue layers called the uveal  15 , the corneoscleral meshwork  16 , and the juxtacanalicular tissue  17 . The juxtacanalicular tissue  17 , in turn, abuts a structure called Schlemm&#39;s canal  18 . The Schlemm&#39;s canal  18  carries a mixture of aqueous humor  8  and blood from the surrounding tissue to drain into the venous system though a system of collector channels  19 . As shown in  FIG.  2   , the vascular layer of the eye, referred to as the choroid  20 , is next to the sclera  2 . A space, called the suprachoroidal space  21 , may be present between the choroid  20  and the suprachoroidal space  21 . The general region near the periphery of the wedge between the cornea  3  and the iris  9 , running circumferentially is called the irido-corneal angle  13 . The irido-corneal angle  13  may also be referred to as the corneal angle of the eye or simply the angle of the eye. The ocular tissues illustrated in  FIG.  3    are all considered to be within the irido-corneal angle  13 . 
     With reference to  FIG.  4   , two possible outflow pathways for the movement of aqueous humor  8  include a trabecular outflow pathway  40  and a uveoscleral outflow pathway  42 . Aqueous humor  8 , which is produced by the ciliary body  6 , flows from the posterior chamber  10  through the pupil into the anterior chamber  7 , and then exits the eye through one or more of the two different outflow pathways  40 ,  42 . Approximately 90% of the aqueous humor  8  leaves via the trabecular outflow pathway  40  by passing through the trabecular meshwork  12 , into the Schlemm&#39;s canal  18  and through one or more plexus of collector channels  19  before draining through a drain path  41  into the venous system. Any remaining aqueous humor  8  leaves primarily through the uveoscleral outflow pathway  42 . The uveoscleral outflow pathway  42  passes through the ciliary body  6  face and iris root into the suprachoroidal space  21  (shown in  FIG.  2   ). Aqueous humor  8  drains from the suprachoroidal space  21 , from which it can be drained through the sclera  2 . 
     Aqueous humor  8  outflow through the trabecular outflow pathway  40  is pressure dependent in that outflow increase as the intraocular pressure increases, whereas aqueous humor  8  outflow through the uveoscleral outflow pathway  42  is pressure independent. Resistance to the outflow of aqueous humor  8  through the trabecular outflow pathway  40  may lead to elevated intra-ocular pressure of the eye, which is a widely recognized risk factor for glaucoma. Resistance through the trabecular outflow pathway  40  may increase due a collapsed Schlemm&#39;s canal  18  or the presence of a high density of collector channels  19 . 
     Referring to  FIG.  5   , as an optical system, the eye  1  is represented by an optical model described by idealized centered and rotationally symmetrical surfaces, entrance and exit pupils, and six cardinal points: object and image space focal points, first and second principal planes, and first and second nodal points. Angular directions relative to the human eye are often defined with respect to an optical axis  24 , a visual axis  26 , a pupillary axis  28  and a line of sight  29  of the eye. The optical axis  24  is the symmetry axis, the line connecting the vertices of the idealized surfaces of the eye. The visual axis  26  connects the foveal center  22  with the first and second nodal points to the object. The line of sight  29  connects the fovea through the exit and entrance pupils to the object. The pupillary axis  28  is normal to the anterior surface of the cornea  3  and directed to the center of the entrance pupil. These axes of the eye differ from one another only by a few degrees and fall within a range of what is generally referred to as the direction of view. 
     Glaucoma 
     Glaucoma is a group of diseases that can harm the optic nerve and cause vision loss or blindness. It is the leading cause of irreversible blindness. Approximately 80 million people are estimated to have glaucoma worldwide and of these, approximately 6.7 million are bilaterally blind. More than 2.7 million Americans over age 40 have glaucoma. Symptoms start with loss of peripheral vision and can progress to blindness. 
     There are two forms of glaucoma, one is referred to as closed-angle glaucoma, the other as open-angled glaucoma. With reference to  FIGS.  1 - 4   , in closed-angle glaucoma, the iris  9  in a collapsed anterior chamber  7  may obstruct and close off the flow of aqueous humor  8 . In open-angle glaucoma, which is the more common form of glaucoma, the permeability of ocular tissue may be affected by blockage of tissue in the irido-corneal angle  13  along the trabecular outflow pathway  40  or by the collapse of the Schlemm&#39;s canal  18  or collector channels  19 . 
     As previously stated, elevated intra-ocular pressure (IOP) of the eye, which damages the optic nerve, is a widely recognized risk factor for glaucoma. However, not every person with increased eye pressure will develop glaucoma, and glaucoma can develop without increased eye pressure. Nonetheless, it is desirable to reduce elevated IOP of the eye to reduce the risk of glaucoma. 
     Methods of diagnosing conditions of the eye of a patient with glaucoma include visual acuity tests and visual field tests, dilated eye exams, tonometry, i.e., measuring the intra-ocular pressure of the eye, and pachymetry, i.e., measuring the thickness of the cornea. Deterioration of vision starts with the narrowing of the visual field and progresses to total blindness. Imaging methods include slit lamp examination, observation of the irido-corneal angle with a gonioscopic lens and optical coherence tomography (OCT) imaging of the anterior chamber and the retina 
     Once diagnosed, some clinically proven treatments are available to control or lower the intra-ocular pressure of the eye to slow or stop the progress of glaucoma. The most common treatments include: 1) medications, such as eye drops or pills, 2) laser surgery, and 3) traditional surgery. Treatment usually begins with medication. However, the efficacy of medication is often hindered by patient non-compliance. When medication does not work for a patient, laser surgery is typically the next treatment to be tried. Traditional surgery is invasive, more high risk than medication and laser surgery, and has a limited time window of effectiveness. Traditional surgery is thus usually reserved as a last option for patients whose eye pressure cannot be controlled with medication or laser surgery. 
     Laser Surgery 
     With reference to  FIG.  2   , laser surgery for glaucoma target the trabecular meshwork  12  to decrease aqueous humor  8  flow resistance and increase aqueous humor outflow. Common laser treatments include Argon Laser Trabeculoplasty (ALT), Selective Laser Trabeculoplasty (SLT) and Excimer Laser Trabeculostomy (ELT). 
     ALT was the first laser trabeculoplasty procedure. During the procedure, an argon laser of 514 nm wavelength is applied to the trabecular meshwork  12  around 180 degrees of the circumference of the irido-corneal angle  13 . The argon laser induces a thermal interaction with the ocular tissue that produces openings in the trabecular meshwork  12 . ALT, however, causes scarring of the ocular tissue, followed by inflammatory responses and tissue healing that may ultimately close the opening through the trabecular meshwork  12  formed by the ALT treatment, thus reducing the efficacy of the treatment. Furthermore, because of this scarring, ALT therapy is typically not repeatable. 
     SLT is designed to lower the scarring effect by selectively targeting pigments in the trabecular meshwork  12  and reducing the amount of heat delivered to surrounding ocular tissue. During the procedure, a solid state laser of 532 nm wavelength is applied to the trabecular meshwork  12  between 180 to 360 degrees around the circumference of the irido-corneal angle  13  to produce openings through the trabecular meshwork  12 . SLT treatment can be repeated, but subsequent treatments have lower effects on IOP reduction. 
     ELT uses a 308 nm wavelength ultraviolet (UV) excimer laser and non-thermal interaction with ocular tissue to treat the trabecular meshwork  12  in a manner that does not invoke a healing response. Therefore, the IOP lowering effect lasts longer. However, because the UV light of the laser cannot penetrate deep into the eye, the laser light is delivered to the trabecular meshwork  12  via an optical fiber inserted into the eye  1  through an opening and the fiber is brought into contact with the trabecular meshwork. The procedure is highly invasive and is generally practiced simultaneously with cataract procedures when the eye is already surgically open. Like ALT and SLT, ELT also lacks control over the amount of IOP reduction. 
     None of these existing laser treatments represents an ideal treatment for glaucoma. Accordingly, what is needed are systems, apparatuses, and method for laser surgery treatment of glaucoma that effectively reduce IOP without significant scarring of tissue, so the treatment may be completed in a single procedure and repeated at a later time if necessary. 
     SUMMARY 
     The present disclosure relates to a method of reducing intraocular pressure in an eye having a cornea, an anterior chamber, and an irido-corneal angle comprising an aqueous humor outflow pathway formed of a trabecular meshwork, a Schlemm&#39;s canal, and one or more collector channels branching from the Schlemm&#39;s canal. The method includes delivering each of an optical coherence tomography (OCT) beam and a laser beam through the cornea, and the anterior chamber into the irido-corneal angle. The method further includes modifying a volume of ocular tissue within the outflow pathway to reduce a pathway resistance present in one or more of the trabecular meshwork, the Schlemm&#39;s canal, and the one or more collector channels by applying the laser beam to ocular tissue defining the volume to thereby cause photo-disruptive interaction with the ocular tissue to reduce the pathway resistance or create a new outflow pathway. The modified volume of ocular tissue provides a channel opening at least partially through the trabecular meshwork. 
     In an aspect of this method, at least a portion of the modified volume of ocular tissue extends between a wall of Schlemm&#39;s canal and the anterior chamber, and the channel opening has a first end in fluid communication with the Schlemm&#39;s canal and a second end in fluid communication with the anterior chamber. In another aspect, the modified volume of ocular tissue extends between a wall of the Schlemm&#39;s canal and a layer of ocular tissue between the anterior chamber and the wall of the Schlemm&#39;s canal, and the channel opening has a first end in fluid communication with the Schlemm&#39;s canal and a second end that terminates in a layer of ocular tissue between the anterior chamber and the wall of the Schlemm&#39;s canal. In yet another aspect, the modified volume of ocular tissue extends between a wall of the anterior chamber and a layer of ocular tissue between the anterior chamber and the wall of the Schlemm&#39;s canal, and the channel opening has a first end in fluid communication with the anterior chamber and a second end that terminates in a layer of ocular tissue between the anterior chamber and the wall of the Schlemm&#39;s canal. 
     The present disclosure also relates to an integrated surgical system for reducing intraocular pressure in an eye having a cornea, an anterior chamber, and an irido-corneal angle comprising an aqueous humor outflow pathway formed of a trabecular meshwork, a Schlemm&#39;s canal, and one or more collector channels branching from the Schlemm&#39;s canal. The system includes a first optical subsystem, a second a first optical subsystem, and a control system. The first optical subsystem includes a focusing objective configured to be coupled to the cornea. The second optical subsystem includes a laser source configured to output a laser beam, and a plurality of components configured to one or more of condition, scan, and direct the laser beam. 
     The control system is coupled to the second optical subsystem and is configured to instruct the laser source to output a laser beam, for delivery through the cornea, and the anterior chamber into the irido-corneal angle. The control system is also configured to instruct the laser source to modify a volume of ocular tissue within the outflow pathway to reduce a pathway resistance present in one or more of the trabecular meshwork, the Schlemm&#39;s canal, and the one or more collector channels by applying the laser beam to ocular tissue defining the volume to thereby cause photo-disruptive interaction with the ocular tissue to reduce the pathway resistance or create a new outflow pathway. The modified volume of ocular tissue provides a channel opening at least partially through the trabecular meshwork. The channel opening may extend through the entirety of the trabecular meshwork or may have an end that terminates within a layer of the trabecular meshwork. 
     The present disclosure also relates to a method of a method of reducing intraocular pressure in an eye having a Schlemm&#39;s canal with fluid therein, and one or more collector channels branching from the Schlemm&#39;s canal. The method includes delivering a laser beam into the Schlemm&#39;s canal, and allowing gases created by photo-disruptive interaction of the laser beam with the fluid inside the Schlemm&#39;s canal to have a pneumatic effect that expands the Schlemm&#39;s canal. Delivering the laser beam into the Schlemm&#39;s canal modifies tissue only inside the Schlemm&#39;s canal without modifying surrounding tissue. 
     In an aspect of this method, locations of the Schlemm&#39;s canal in which to deliver the laser beam are determined. The eye comprises a circumferential angle and or more locations of the Schlemm&#39;s canal for laser beam delivery are determined by obtaining images of the Schlemm&#39;s canal at a plurality of locations around at least a portion of the circumferential angle, processing each of the images to determine a measure of an anatomical feature of the Schlemm&#39;s canal, and designating the location from which the image was obtained as a location of the Schlemm&#39;s canal for laser beam delivery based on an evaluation of the determined measure relative to a threshold measure. 
     In another aspect, the method further includes monitoring the Schlemm&#39;s canal for an acceptable pneumatic expansion, and stopping the delivering of the laser beam when an acceptable pneumatic expansion is detected. Such monitoring may be involve obtaining OCT images of the Schlemm&#39;s canal while the laser beam is being delivered, processing the images to obtain measures indicative of pneumatic expansion of the canal and evaluating the images relative to a criterion of an acceptable pneumatic expansion. 
     The present disclosure also relates to an integrated surgical system for reducing intraocular pressure in an eye having a cornea, a Schlemm&#39;s canal with fluid therein, and one or more collector channels branching from the Schlemm&#39;s canal. The system includes a first optical subsystem, a second a first optical subsystem, and a control system. The first optical subsystem includes a focusing objective configured to be coupled to the cornea. The second optical subsystem includes a laser source configured to output a laser beam, and a plurality of components configured to one or more of condition, scan, and direct the laser beam; and 
     The control system is coupled to the second optical subsystem and configured to instruct the laser source to output a laser beam, for delivery through the first optical subsystem and the cornea, and into the Schlemm&#39;s canal. The control system is also configured to allow gases created by photo-disruptive interaction of the laser beam with the fluid inside the Schlemm&#39;s canal to have a pneumatic effect that expands the Schlemm&#39;s canal. Delivering the laser beam into the Schlemm&#39;s canal modifies tissue only inside the Schlemm&#39;s canal without modifying surrounding tissue. 
     In an aspect of this system, the control system is further configured to identify one or more locations of the Schlemm&#39;s canal in which to deliver the laser beam. In another aspect, the control system is further configured to monitor the Schlemm&#39;s canal for an acceptable pneumatic expansion, and instruct the laser source to stop the output of the laser beam when an acceptable pneumatic expansion is detected. 
     It is understood that other aspects of apparatuses and methods will become apparent to those skilled in the art from the following detailed description, wherein various aspects of apparatuses and methods are shown and described by way of illustration. As will be realized, these aspects may be implemented in other and different forms and its several details are capable of modification in various other respects. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various aspects of systems, apparatuses, and methods will now be presented in the detailed description by way of example, and not by way of limitation, with reference to the accompanying drawings, wherein: 
         FIG.  1    is a sectional schematic illustration of a human eye and its interior anatomical structures. 
         FIG.  2    is a sectional schematic illustration of the irido-corneal angle of the eye of  FIG.  1   . 
         FIG.  3    is a sectional schematic illustration detailing anatomical structures in the irido-corneal angle of  FIG.  2   , including the trabecular meshwork, Schlemm&#39;s canal, and one or more collector channels branching from the Schlemm&#39;s canal. 
         FIG.  4    is a sectional schematic illustration of various outflow pathways for aqueous humor through the trabecular meshwork, Schlemm&#39;s canal, and collector channels of  FIG.  3   . 
         FIG.  5    is a sectional schematic illustration of a human eye showing various axes associated with the eye. 
         FIG.  6    is a sectional schematic illustration of an angled beam path along which one or more light beams may access the irido-corneal angle of the eye. 
         FIG.  7    is a block diagram of an integrated surgical system for non-invasive glaucoma surgery including a control system, a femtosecond laser source, an OCT imaging apparatus, a microscope, beam conditioners and scanners, beam combiners, a focusing objective, and a patient interface. 
         FIG.  8    is a detailed block diagram of the integrated surgical system of  FIG.  7   . 
         FIGS.  9 A and  9 B  are schematic illustrations of the focusing objective of the integrated surgical system of  FIG.  7    coupled to ( FIG.  9 A ) and decoupled from ( FIG.  9 B ) the patient interface of the integrated surgical system of  FIG.  7   . 
         FIG.  9 C  is a schematic illustration of components of the focusing objective and the patient interface included in  FIGS.  9 A and  9 B . 
         FIGS.  10 A and  10 B  are schematic illustrations of components of the integrated surgical system of  FIGS.  7  and  8    functionally arranged to form a first optical system and a second optical subsystem that enable access to the to the irido-corneal angle along the angled beam path of  FIG.  6   . 
         FIG.  10 C  is a schematic illustration of a beam passing through the first optical subsystem of  FIGS.  10 A and  10 B  and into the eye. 
         FIG.  11 A  is a schematic illustration of a treatment pattern designed by the integrated surgical system of  FIG.  7    to affect a surgical volume of ocular tissue. 
         FIG.  11 B  is a schematic illustration of an outflow pathway characterized by a deep channel opening that results from laser application of the treatment pattern of  FIG.  11 A . 
         FIG.  11 C  is a three-dimensional schematic illustration of the outflow pathway of  FIG.  11 B . 
         FIG.  12    is a flowchart of a method of modifying ocular tissue at the irido-corneal angle of the eye. 
         FIG.  13    is a flowchart of a method of delivering light beams to the irido-corneal angle of the eye along the angled beam path of  FIG.  6   . 
         FIG.  14 A  is a schematic illustration of a treatment pattern designed by the integrated surgical system of  FIG.  7    to affect a surgical volume of ocular tissue. 
         FIG.  14 B  is a schematic illustration of an outflow pathway characterized by a shallow channel opening that results from laser application of the treatment pattern of  FIG.  14 A . 
         FIG.  14 C  is a three-dimensional schematic illustration of the outflow pathway of  FIG.  14 B . 
         FIG.  15 A  is a schematic illustration of a treatment pattern designed by the integrated surgical system of  FIG.  7    to affect an array of surgical volumes of ocular tissue. 
         FIG.  15 B  is a schematic illustration of an array of outflow pathways, each characterized by a shallow channel opening, that results from laser application of the treatment pattern of  FIG.  15 A . 
         FIG.  15 C  is a three-dimensional schematic illustration of the array of outflow pathways of  FIG.  15 B . 
         FIG.  16 A  is a schematic illustration of a partially collapsed Schlemm&#39;s canal. 
         FIG.  16 B  is a schematic illustration of a treatment pattern designed by the integrated surgical system of  FIG.  7    to induce a pneumatic expansion of the Schlemm&#39;s canal. 
         FIG.  17    is a graph displaying the dependence between the rate of entry of the newly formed aqueous humor into the anterior chamber (F) and the rate of outflow of aqueous humor (I) as a function of a pressure differential (Pi−Pe) and collective hydraulic conductivity (C). 
         FIG.  18    is an electrical circuit model for aqueous flow. 
         FIG.  19 A  is an electrical circuit model of aqueous flow, wherein values of resistors are changed to model the treatment pattern resulting in the deep channel opening shown in  FIG.  11 B . 
         FIG.  19 B  is an electrical circuit model of aqueous flow, wherein values of resistors are changed to model the treatment pattern resulting in the shallow channel opening shown in  FIG.  14 B . 
         FIG.  19 C  is an electrical circuit model of aqueous flow, wherein values of resistors are changed to model the treatment pattern resulting in the pneumatic expansion of the Schlemm&#39;s canal shown in  FIG.  16 B . 
         FIGS.  20 A- 20 C  are variations of the electrical circuit model of  FIG.  18   , wherein circuit components are removed based on one or more assumptions related to aqueous flow. 
         FIG.  21    is a flowchart of a method of designing a treatment pattern using the aqueous flow model of  FIG.  18   . 
         FIG.  22    is a flowchart of a method of modifying ocular tissue at the irido-corneal angle of the eye using the treatment pattern designed by the method of  FIG.  21   . 
     
    
    
     DETAILED DESCRIPTION 
     Disclosed herein are systems, apparatuses, and methods for safely and effectively reducing intra-ocular pressure (IOP) in the eye to either treat or reduce the risk of glaucoma. The systems, apparatuses, and methods enable access to the irido-corneal angle of the eye and integrate laser surgery techniques with high resolution imaging to precisely diagnose, locate, and treat abnormal ocular tissue conditions within the irido-corneal angle that may be causing elevated IOP. 
     An integrated surgical system disclosed herein is configured to reduce intraocular pressure in an eye having a cornea, an anterior chamber, and an irido-corneal angle comprising an aqueous humor outflow pathway formed of a trabecular meshwork, a Schlemm&#39;s canal, and one or more collector channels branching from the Schlemm&#39;s canal. The integrated surgical system also includes a first optical subsystem and a second optical subsystem. The first optical subsystem includes a window configured to be coupled to the cornea and an exit lens configured to be coupled to the window. The second optical subsystem includes an optical coherence tomography (OCT) imaging apparatus configured to output an OCT beam, a laser source configured to output a laser beam, and a plurality of components, e.g., lenses and mirrors, configured to condition, combine, or direct the OCT beam and the laser beam toward the first optical subsystem. 
     The integrated surgical system also includes a control system coupled to the OCT imaging apparatus, the laser source, and the second optical subsystem. The controller is configured to instruct the OCT imaging apparatus to output an OCT beam and the laser source to output a laser beam, for delivery through the cornea, and the anterior chamber into the irido-corneal angle. In one configuration, the control system controls the second optical subsystem, so the OCT beam and the laser beam are directed into the first optical subsystem along a second optical axis that is offset from the first optical axis and that extends into the irido-corneal angle along an angled beam path  30 . 
     Directing each of an OCT beam and a laser beam along the same second optical axis into the irido-corneal angle of the eye is beneficial in that it enables direct application of the result of the evaluation of the condition into the treatment plan and surgery with precision in one clinical setting. Furthermore, combining OCT imaging and laser treatment allows targeting the ocular tissue with precision not available with any existing surgical systems and methods. Surgical precision afforded by the integrated surgical system allows for the affecting of only the targeted tissue of microscopic size and leaves the surrounding tissue intact. The microscopic size scale of the affected ocular tissue to be treated in the irido-corneal angle of the eye ranges from a few micrometers to a few hundred micrometers. For example, with reference to  FIGS.  2  and  3   , the cross-sectional size of the normal Schlemm&#39;s canal  18  is an oval shape of a few tens of micrometers by a few hundred micrometers. The diameter of collector channels  19  and veins is a few tens of micrometers. The thickness of the juxtacanalicular tissue  17  is a few micrometers, the thickness of the trabecular meshwork  12  is around a hundred micrometers. 
     The control system of the integrated surgical system is further configured to instruct the laser source to modify a volume of ocular tissue within the outflow pathway to reduce a pathway resistance present in one or more of the trabecular meshwork, the Schlemm&#39;s canal, and the one or more collector channels by applying the laser beam to ocular tissue defining the volume to thereby cause photo-disruptive interaction with the ocular tissue to reduce the pathway resistance or create a new outflow pathway. 
     The laser source may be a femtosecond laser. Femtosecond lasers provide non-thermal photo-disruption interaction with ocular tissue to avoid thermal damage to surrounding tissue. Further, unlike other surgical methods, with femtosecond laser treatment opening surface incisions penetrating the eye can be avoided, enabling a non-invasive treatment. Instead of performing the treatment in a sterile surgical room, the non-invasive treatment can be performed in a non-sterile outpatient facility. 
     An additional imaging component may be included the integrated surgical system to provide direct visual observation of the irido-corneal angle along an angle of visual observation. For example, a microscope or imaging camera may be included to assist the surgeon in the process of docking the eye to the patient interface or an immobilizing device, location of ocular tissues in the eye and observing the progress of the surgery. The angle of visual observation can also be along the angled beam path  30  to the irido-corneal angle  13  through the cornea  3  and the anterior chamber  7 . 
     Images from the OCT imaging apparatus and the additional imaging component providing visual observation, e.g. microscope, are combined on a display device such as a computer monitor. Different images can be registered and overlaid on a single window, enhanced, processed, differentiated by false color for easier understanding. Certain features are computationally recognized by a computer processor, image recognition and segmentation algorithm can be enhanced, highlighted, marked for display. The geometry of the treatment plan can also be combined and registered with imaging information on the display device and marked up with geometrical, numerical and textual information. The same display can also be used for user input of numerical, textual and geometrical nature for selecting, highlighting and marking features, inputting location information for surgical targeting by keyboard, mouse, cursor, touchscreen, audio or other user interface devices. 
     OCT Imaging 
     The main imaging component of the integrated surgical system disclosed herein is an OCT imaging apparatus. OCT technology may be used to diagnose, locate and guide laser surgery directed to the irido-corneal angle of the eye. For example, with reference to  FIGS.  1 - 3   , OCT imaging may be used to determine the structural and geometrical conditions of the anterior chamber  7 , to assess possible obstruction of the trabecular outflow pathway  40  and to determine the accessibility of the ocular tissue for treatment. As previously described, the iris  9  in a collapsed anterior chamber  7  may obstruct and close off the flow of aqueous humor  8 , resulting in closed-angle glaucoma. In open-angle glaucoma, where the macroscopic geometry of the angle is normal, the permeability of ocular tissue may be affected, by blockage of tissue along the trabecular outflow pathway  40  or by the collapse of the Schlemm&#39;s canal  18  or collector channels  19 . 
     OCT imaging can provide the necessary spatial resolution, tissue penetration and contrast to resolve microscopic details of ocular tissue. When scanned, OCT imaging can provide two-dimensional (2D) cross-sectional images of the ocular tissue. As another aspect of the integrated surgical system, 2D cross-sectional images may be processed and analyzed to determine the size, shape and location of structures in the eye for surgical targeting. It is also possible to reconstruct three-dimensional (3D) images from a multitude of 2D cross-sectional images but often it is not necessary. Acquiring, analyzing and displaying 2D images is faster and can still provide all information necessary for precise surgical targeting. 
     OCT is an imaging modality capable of providing high resolution images of materials and tissue. Imaging is based on reconstructing spatial information of the sample from spectral information of scattered light from within the sample. Spectral information is extracted by using an interferometric method to compare the spectrum of light entering the sample with the spectrum of light scattered from the sample. Spectral information along the direction that light is propagating within the sample is then converted to spatial information along the same axis via the Fourier transform. Information lateral to the OCT beam propagation is usually collected by scanning the beam laterally and repeated axial probing during the scan. 2D and 3D images of the samples can be acquired this way. Image acquisition is faster when the interferometer is not mechanically scanned in a time domain OCT, but interference from a broad spectrum of light is recorded simultaneously, this implementation is called a spectral domain OCT. Faster image acquisition may also be obtained by scanning the wavelength of light rapidly from a wavelength scanning laser in an arrangement called a swept-source OCT. 
     The axial spatial resolution limit of the OCT is inversely proportional to the bandwidth of the probing light used. Both spectral domain and swept source OCTs are capable of axial spatial resolution below 5 micrometers (μm) with sufficiently broad bandwidth of 100 nanometers (nm) or more. In the spectral domain OCT, the spectral interference pattern is recorded simultaneously on a multichannel detector, such as a charge coupled device (CCD) or complementary metal oxide semiconductor (CMOS) camera, while in the swept source OCT the interference pattern is recorded in sequential time steps with a fast optical detector and electronic digitizer. There is some acquisition speed advantage of the swept source OCT but both types of systems are evolving and improving rapidly, and resolution and speed is sufficient for purposes of the integrated surgical system disclosed herein. Stand-alone OCT systems and OEM components are now commercially available from multiple vendors, such as Optovue Inc., Fremont, Calif., Topcon Medical Systems, Oakland, N.J., Carl Zeiss Meditec AG, Germany, Nidek, Aichi, Japan, Thorlabs, Newton, N.J., Santec, Aichi, Japan, Axsun, Billercia, Mass., and other vendors. 
     Femtosecond Laser Source 
     The preferred surgical component of the integrated surgical system disclosed herein is a femtosecond laser. A femtosecond laser provides highly localized, non-thermal photo-disruptive laser-tissue interaction with minimal collateral damage to surrounding ocular tissue. Photo-disruptive interaction of the laser is utilized in optically transparent tissue. The principal mechanism of laser energy deposition into the ocular tissue is not by absorption but by a highly nonlinear multiphoton process. This process is effective only at the focus of the pulsed laser where the peak intensity is high. Regions where the beam is traversed but not at the focus are not affected by the laser. Therefore, the interaction region with the ocular tissue is highly localized both transversally and axially along the laser beam. The process can also be used in weakly absorbing or weakly scattering tissue. While femtosecond lasers with photo-disruptive interactions have been successfully used in ophthalmic surgical systems and commercialized in other ophthalmic laser procedures, none have been used in an integrated surgical system that accesses the irido-corneal angle. 
     In known refractive procedures, femtosecond lasers are used to create corneal flaps, pockets, tunnels, arcuate incisions, lenticule shaped incisions, partial or fully penetrating corneal incisions for keratoplasty. For cataract procedures the laser creates a circular cut on the capsular bag of the eye for capsulotomy and incisions of various patterns in the lens for braking up the interior of the crystalline lens to smaller fragments to facilitate extraction. Entry incisions through the cornea opens the eye for access with manual surgical devices and for insertions of phaco emulsification devices and intra-ocular lens insertion devices. Several companies have commercialized such surgical systems, among them the Intralase system now available from Johnson &amp; Johnson Vision, Santa Ana, Calif., The LenSx and Wavelight systems from Alcon, Fort Worth, Tex., other surgical systems from Bausch and Lomb, Rochester, N.Y., Carl Zeiss Meditec AG, Germany, Ziemer, Port, Switzerland, and LensAR, Orlando, Fla. 
     These existing systems are developed for their specific applications, for surgery in the cornea, and the crystalline lens and its capsular bag and are not capable of performing surgery in the irido-corneal angle  13  for several reasons. First, the irido-corneal angle  13  is not accessible with these surgical laser systems because the irido-corneal angle is too far out in the periphery and is outside of surgical range of these systems. Second, the angle of the laser beam from these systems, which is along the optical axis  24  to the eye, is not appropriate to reaching the irido-corneal angle  13 , where there is significant scattering and optical distortion at the applied wavelength. Third, any imaging capabilities these systems may have do not have the accessibility, penetration depth and resolution to image the tissue along the trabecular outflow pathway  40  with sufficient detail and contrast. 
     In accordance with the integrated surgical system disclosed herein, clear access to the irido-corneal angle  13  is provided along the angled beam path  30 . The tissue, e.g., cornea  3  and the aqueous humor  8  in the anterior chamber  7 , along this angled beam path  30  is transparent for wavelengths from approximately 400 nm to 2500 nm and femtosecond lasers operating in this region can be used. Such mode locked lasers work at their fundamental wavelength with Titanium, Neodymium or Ytterbium active material. Non-linear frequency conversion techniques known in the art, frequency doubling, tripling, sum and difference frequency mixing techniques, optical parametric conversion can convert the fundamental wavelength of these lasers to practically any wavelength in the above mentioned transparent wavelength range of the cornea. 
     Existing ophthalmic surgical systems apply lasers with pulse durations longer than 1 ns have higher photo-disruption threshold energy, require higher pulse energy and the dimension of the photo-disruptive interaction region is larger, resulting in loss of precision of the surgical treatment. When treating the irido-corneal angle  13 , however, higher surgical precision is required. To this end, the integrated surgical system may be configured to apply lasers with pulse durations from 10 femtosecond (fs) to 1 nanosecond (ns) for generating photo-disruptive interaction of the laser beam with ocular tissue in the irido-corneal angle  13 . While lasers with pulse durations shorter than 10 fs are available, such laser sources are more complex and more expensive. Lasers with the described desirable characteristics, e.g., pulse durations from 10 femtosecond (fs) to 1 nanosecond (ns), are commercially available from multiple vendors, such as Newport, Irvine, Calif., Coherent, Santa Clara, Calif., Amplitude Systems, Pessac, France, NKT Photonics, Birkerod, Denmark, and other vendors. 
     Accessing the Irido-Corneal Angle 
     An important feature afforded by the integrated surgical system is access to the targeted ocular tissue in the irido-corneal angle  13 . With reference to  FIG.  6   , the irido-corneal angle  13  of the eye may be accessed via the integrated surgical system along an angled beam path  30  passing through the cornea  3  and through the aqueous humor  8  in the anterior chamber  7 . For example, one or more of an imaging beam, e.g., an OCT beam and/or a visual observation beam, and a laser beam may access the irido-corneal angle  13  of the eye along the angled beam path  30 . 
     An optical system disclosed herein is configured to direct a light beam to an irido-corneal angle  13  of an eye along an angled beam path  30 . The optical system includes a first optical subsystem and a second optical subsystem. The first optical subsystem includes a window formed of a material with a refractive index n w  and has opposed concave and convex surfaces. The first optical subsystem also includes an exit lens formed of a material having a refractive index n x . The exit lens also has opposed concave and convex surfaces. The concave surface of the exit lens is configured to couple to the convex surface of the window to define a first optical axis extending through the window and the exit lens. The concave surface of the window is configured to detachably couple to a cornea of the eye with a refractive index n c  such that, when coupled to the eye, the first optical axis is generally aligned with the direction of view of the eye. 
     The second optical subsystem is configured to output a light beam, e.g., an OCT beam or a laser beam. The optical system is configured so that the light beam is directed to be incident at the convex surface of the exit lens along a second optical axis at an angle α that is offset from the first optical axis. The respective geometries and respective refractive indices n x , and n w  of the exit lens and window are configured to compensate for refraction and distortion of the light beam by bending the light beam so that it is directed through the cornea  3  of the eye toward the irido-corneal angle  13 . More specifically, the first optical system bends the light beam to that the light beam exits the first optical subsystem and enters the cornea  3  at an appropriate angle so that the light beam progresses through the cornea and the aqueous humor  8  in a direction along the angled beam path  30  toward the irido-corneal angle  13 . 
     Accessing the irido-corneal angle  13  along the angled beam path  30  provides several advantages. An advantage of this angled beam path  30  to the irido-corneal angle  13  is that the OCT beam and laser beam passes through mostly clear tissue, e.g., the cornea  3  and the aqueous humor  8  in the anterior chamber  7 . Thus, scattering of these beams by tissue is not significant. With respect to OCT imaging, this enables the use of shorter wavelength, less than approximately 1 micrometer, for the OCT to achieve higher spatial resolution. An additional advantage of the angled beam path  30  to the irido-corneal angle  13  through the cornea  3  and the anterior chamber  7  is the avoidance of direct laser beam or OCT beam light illuminating the retina  11 . As a result, higher average power laser light and OCT light can be used for imaging and surgery, resulting in faster procedures and less tissue movement during the procedure. 
     Another important feature provided by the integrated surgical system is access to the targeted ocular tissue in the irido-corneal angle  13  in a way that reduces beam discontinuity. To this end, the window and exit lens components of the first optical subsystem are configured to reduce the discontinuity of the optical refractive index between the cornea  3  and the neighboring material and facilitate entering light through the cornea at a steep angle. 
     Having thus generally described the integrated surgical system and some of its features and advantages, a more detailed description of the system and its component parts follows. 
     Integrated Surgical System 
     With reference to  FIG.  7   , an integrated surgical system  1000  for non-invasive glaucoma surgery includes a control system  100 , a surgical component  200 , a first imaging component  300  and an optional second imaging component  400 . In the embodiment of  FIG.  7   , the surgical component  200  is a femtosecond laser source, the first imaging component  300  is an OCT imaging apparatus, and the optional second imaging component  400  is a visual observation apparatus, e.g., a microscope, for direct viewing or viewing with a camera. Other components of the integrated surgical system  1000  include beam conditioners and scanners  500 , beam combiners  600 , a focusing objective  700 , and a patient interface  800 . 
     The control system  100  may be a single computer or and plurality of interconnected computers configured to control the hardware and software components of the other components of the integrated surgical system  1000 . A user interface  110  of the control system  100  accepts instructions from a user and displays information for observation by the user. Input information and commands from the user include but are not limited to system commands, motion controls for docking the patient&#39;s eye to the system, selection of pre-programmed or live generated surgical plans, navigating through menu choices, setting of surgical parameters, responses to system messages, determining and acceptance of surgical plans and commands to execute the surgical plan. Outputs from the system towards the user includes but are not limited to display of system parameters and messages, display of images of the eye, graphical, numerical and textual display of the surgical plan and the progress of the surgery. 
     The control system  100  is connected to the other components  200 ,  300 ,  400 ,  500  of the integrated surgical system  1000 . Control signals from the control system  100  to the femtosecond laser source  200  function to control internal and external operation parameters of the laser source, including for example, power, repetition rate and beam shutter. Control signals from the control system  100  to the OCT imaging apparatus  300  function to control OCT beam scanning parameters, and the acquiring, analyzing and displaying of OCT images. 
     Laser beams  201  from the femtosecond laser source  200  and OCT beams  301  from the OCT imaging apparatus  300  are directed towards a unit of beam conditioners and scanners  500 . Different kind of scanners can be used for the purpose of scanning the laser beam  201  and the OCT beam  301 . For scanning transversal to a beam  201 ,  301 , angular scanning galvanometer scanners are available for example from Cambridge Technology, Bedford, Mass., Scanlab, Munich, Germany. To optimize scanning speed, the scanner mirrors are typically sized to the smallest size, which still support the required scanning angles and numerical apertures of the beams at the target locations. The ideal beam size at the scanners is typically different from the beam size of the laser beam  201  or the OCT beam  301 , and different from what is needed at the entrance of a focusing objective  700 . Therefore, beam conditioners are applied before, after or in between individual scanners. The beam conditioner and scanners  500  includes scanners for scanning the beam transversally and axially. Axial scanning changes the depth of the focus at the target region. Axial scanning can be performed by moving a lens axially in the beam path with a servo or stepper motor. 
     The laser beam  201  and the OCT beam  301  are combined with dichroic, polarization or other kind of beam combiners  600  to reach a common target volume or surgical volume in the eye. In an integrated surgical system  1000  having a femtosecond laser source  200 , an OCT imaging apparatus  300 , and a visual observation device  400 , the individual beams  201 ,  301 ,  401  for each of these components may be individually optimized and may be collinear or non-collinear to one another. The beam combiner  600  uses dichroic or polarization beam splitters to split and recombine light with different wavelength and/or polarization. The beam combiner  600  may also include optics to change certain parameters of the individual beams  201 ,  301 ,  401  such as beam size, beam angle and divergence. Integrated visual illumination, observation or imaging devices assist the surgeon in docking the eye to the system and identifying surgical locations. 
     To resolve ocular tissue structures of the eye in sufficient detail, the imaging components  300 ,  400  of the integrated surgical system  1000  may provide an OCT beam and a visual observation beam having a spatial resolution of several micrometers. The resolution of the OCT beam is the spatial dimension of the smallest feature that can be recognized in the OCT image. It is determined mostly by the wavelength and the spectral bandwidth of the OCT source, the quality of the optics delivering the OCT beam to the target location in the eye, the numerical aperture of the OCT beam and the spatial resolution of the OCT imaging apparatus at the target location. In one embodiment, the OCT beam of the integrated surgical system has a resolution of no more than 5 μm. 
     Likewise, the surgical laser beam provided by the femtosecond laser source  200  may be delivered to targeted locations with several micrometer accuracy. The resolution of the laser beam is the spatial dimension of the smallest feature at the target location that can be modified by the laser beam without significantly affecting surrounding ocular tissue. It is determined mostly by the wavelength of the laser beam, the quality of the optics delivering the laser beam to target location in the eye, the numerical aperture of the laser beam, the energy of the laser pulses in the laser beam and the spatial resolution of the laser scanning system at the target location. In addition, to minimize the threshold energy of the laser for photo-disruptive interaction, the size of the laser spot should be no more than approximately 5 μm. 
     It should be noted that, while the visual observation beam  401  is acquired by the visual observation device  400  using fixed, non-scanning optics, the OCT beam  301  of the OCT imaging apparatus  300  is scanned laterally in two transversal directions. The laser beam  201  of the femtosecond laser source  200  is scanned in two lateral dimensions and the depth of the focus is scanned axially. 
     For practical embodiments, beam conditioning, scanning and combining the optical paths are certain functions performed on the laser, OCT and visual observation optical beams. Implementation of those functions may happen in a different order than what is indicated in  FIG.  7   . Specific optical hardware that manipulates the beams to implement those functions can have multiple arrangements with regards to how the optical hardware is arranged. They can be arranged in a way that they manipulate individual optical beams separately, in another embodiment one component may combine functions and manipulates different beams. For example, a single set of scanners can scan both the laser beam  201  and the OCT beam  301 . In this case, separate beam conditioners set the beam parameters for the laser beam  201  and the OCT beam  301 , then a beam combiner combines the two beams for a single set of scanners to scan the beams. While many combinations of optical hardware arrangements are possible for the integrated surgical system, the following section describes in detail an example arrangement. 
     Beam Delivery 
     In the following description, the term beam may—depending on the context—refer to one of a laser beam, an OCT beam, or a visual observation beam. A combined beam refers to two or more of a laser beam, an OCT beam, or a visual observation beam that are either collinearly combined or non-collinearly combined. Example combined beams include a combined OCT/laser beam, which is a collinear or non-colinear combination of an OCT beam and a laser beam, and a combined OCT/laser/visual beam, which is a collinear or non-collinear combination of an OCT beam, a laser beam, and a visual beam. In a collinearly combined beam, the different beams may be combined by dichroic or polarization beam splitters, and delivered along a same optical path through a multiplexed delivery of the different beams. In a non-collinear combined beam, the different beams are delivered at the same time along different optical paths that are separated spatially or by an angle between them. In the description to follow, any of the foregoing beams or combined beams may be generically referred to as a light beam. The terms distal and proximal may be used to designate the direction of travel of a beam, or the physical location of components relative to each other within the integrated surgical system. The distal direction refers to a direction toward the eye; thus an OCT beam output by the OCT imaging apparatus moves in the distal direction toward the eye. The proximal direction refers to a direction away from the eye; thus an OCT return beam from the eye moves in the proximal direction toward the OCT imaging apparatus. 
     Referring to  FIG.  8   , an example integrated surgical system is configured to deliver each of a laser beam  201  and an OCT beam  301  in the distal direction toward an eye  1 , and receive each of an OCT return beam and the visual observation beam  401  back from the eye  1 . Regarding the delivery of a laser beam, a laser beam  201  output by the femtosecond laser source  200  passes through a beam conditioner  510  where the basic beam parameters, beam size, divergence are set. The beam conditioner  510  may also include additional functions, setting the beam power or pulse energy and shutter the beam to turn it on or off After existing the beam conditioner  510 , the laser beam  210  enters an axial scanning lens  520 . The axial scanning lens  520 , which may include a single lens or a group of lenses, is movable in the axial direction  522  by a servo motor, stepper motor or other control mechanism. Movement of the axial scanning lens  520  in the axial direction  522  changes the axial distance of the focus of the laser beam  210  at a focal point. 
     In accordance with a particular embodiment of the integrated surgical system, an intermediate focal point  722  is set to fall within, and is scannable in, the conjugate surgical volume  721 , which is an image conjugate of the surgical volume  720 , determined by the focusing objective  700 . The surgical volume  720  is the spatial extent of the region of interest within the eye where imaging and surgery is performed. For glaucoma surgery, the surgical volume  720  is the vicinity of the irido-corneal angle  13  of the eye. 
     A pair of transverse scanning mirrors  530 ,  532  rotated by a galvanometer scanner scan the laser beam  201  in two essentially orthogonal transversal directions, e.g., in the x and y directions. Then the laser beam  201  is directed towards a dichroic or polarization beam splitter  540  where it is reflected toward a beam combining mirror  601  configured to combine the laser beam  201  with an OCT beam  301 . 
     Regarding delivery of an OCT beam, an OCT beam  301  output by the OCT imaging apparatus  300  passes through a beam conditioner  511 , an axially moveable focusing lens  521  and a transversal scanner with scanning mirrors  531  and  533 . The focusing lens  521  is used set the focal position of the OCT beam in the conjugate surgical volume  721  and the real surgical volume  720 . The focusing lens  521  is not scanned for obtaining an OCT axial scan. Axial spatial information of the OCT image is obtained by Fourier transforming the spectrum of the interferometrically recombined OCT return beam  301  and reference beams  302 . However, the focusing lens  521  can be used to re-adjust the focus when the surgical volume  720  is divided into several axial segments. This way the optimal imaging spatial resolution of the OCT image can be extended beyond the Rayleigh range of the OCT signal beam, at the expense of time spent on scanning at multiple ranges. 
     Proceeding in the distal direction toward the eye  1 , after the scanning mirrors  531  and  533 , the OCT beam  301  is combined with the laser beam  201  by the beam combiner mirror  601 . The OCT beam  301  and laser beam  201  components of the combined laser/OCT beam  550  are multiplexed and travel in the same direction to be focused at an intermediate focal point  722  within the conjugate surgical volume  721 . After having been focused in the conjugate surgical volume  721 , the combined laser/OCT beam  550  propagates to a second beam combining mirror  602  where it is combined with a visual observation beam  401  to form a combined laser/OCT/visual beam  701 . 
     The combined laser/OCT/visual beam  701  traveling in the distal direction then passes through the focusing objective  700 , and a window  801  of a patient interface, where the intermediate focal point  722  of the laser beam within the conjugate surgical volume  721  is re-imaged into a focal point in the surgical volume  720 . The focusing objective  700  re-images the intermediate focal point  722 , through the window  801  of a patient interface, into the ocular tissue within the surgical volume  720 . 
     A scattered OCT return beam  301  from the ocular tissue travels in the proximal direction to return to the OCT imaging apparatus  300  along the same paths just described, in reverse order. The reference beam  302  of the OCT imaging apparatus  300 , passes through a reference delay optical path and return to the OCT imaging apparatus from a moveable mirror  330 . The reference beam  302  is combined interferometrically with the OCT return beam  301  on its return within the OCT imaging apparatus  300 . The amount of delay in the reference delay optical path is adjustable by moving the moveable mirror  330  to equalize the optical paths of the OCT return beam  301  and the reference beam  302 . For best axial OCT resolution, the OCT return beam  301  and the reference beam  302  are also dispersion compensated to equalize the group velocity dispersion within the two arms of the OCT interferometer. 
     When the combined laser/OCT/visual beam  701  is delivered through the cornea  3  and the anterior chamber  7 , the combined beam passes through posterior and anterior surface of the cornea at a steep angle, far from normal incidence. These surfaces in the path of the combined laser/OCT/visual beam  701  create excessive astigmatism and coma aberrations that need to be compensated for. 
     With reference to  FIGS.  9 A and  9 B , in an embodiment of the integrated surgical system  1000 , optical components of the focusing objective  700  and patient interface  800  are configured to minimize spatial and chromatic aberrations and spatial and chromatic distortions.  FIG.  9 A  shows a configuration when both the eye  1 , the patient interface  800  and the focusing objective  700  all coupled together.  FIG.  9 B  shows a configuration when both the eye  1 , the patient interface  800  and the focusing objective  700  all detached from one another. 
     The patient interface  800  optically and physically couples the eye  1  to the focusing objective  700 , which in turn optically couples with other optic components of the integrated surgical system  1000 . The patient interface  800  serves multiple functions. It immobilizes the eye relative to components of the integrated surgical system; creates a sterile barrier between the components and the patient; and provides optical access between the eye and the instrument. The patient interface  800  is a sterile, single use disposable device and it is coupled detachably to the eye  1  and to the focusing objective  700  of the integrated surgical system  1000 . 
     The patient interface  800  includes a window  801  having an eye-facing, concave surface  812  and an objective-facing, convex surface  813  opposite the concave surface. The window  801  thus has a meniscus form. With reference to  FIG.  9 C , the concave surface  812  is characterized by a radius of curvature r e , while the convex surface  813  is characterized by a radius of curvature r w . The concave surface  812  is configured to couple to the eye, either through a direct contact or through index matching material, liquid or gel, placed in between the concave surface  812  and the eye  1 . The window  801  may be formed of glass and has a refractive index n w . In one embodiment, the window  801  is formed of fused silica and has a refractive index n w  of 1.45. Fused silica has the lowest index from common inexpensive glasses. Fluoropolymers such as the Teflon AF are another class of low index materials that have refractive indices lower than fused silica, but their optical quality is inferior to glasses and they are relatively expensive for high volume production. In another embodiment the window  801  is formed of the common glass BK7 and has a refractive index of 1.50. A radiation resistant version of this glass, BK7G18 from Schott AG, Mainz, Germany, allows gamma sterilization of the patient interface  800  without the gamma radiation altering the optical properties of the window  801 . 
     Returning to  FIGS.  9 A and  9 B , the window  801  is surrounded by a wall  803  of the patient interface  800  and an immobilization device, such as a suction ring  804 . When the suction ring  804  is in contact with the eye  1 , an annular cavity  805  is formed between the suction ring and the eye. When vacuum applied to the suction ring  804  and the cavity via a vacuum tube a vacuum pump (not shown in  FIGS.  9 A and  9 B ), vacuum forces between the eye and the suction ring attach the eye to the patient interface  800  during surgery. Removing the vacuum releases or detach the eye  1 . 
     The end of the patient interface  800  opposite the eye  1  includes an attachment interface  806  configured to attach to the housing  702  of the focusing objective  700  to thereby affix the position of the eye relative to the other components of the integrated surgical system  1000 . The attachment interface  806  can work with mechanical, vacuum, magnetic or other principles and it is also detachable from the integrated surgical system. 
     The focusing objective  700  includes an aspheric exit lens  710  having an eye-facing, concave surface  711  and a convex surface  712  opposite the concave surface. The exit lens  710  thus has a meniscus form. While the exit lens  710  shown in  FIGS.  9 A and  9 B  is an aspheric lens giving more design freedom, in other configurations the exit lens may be a spherical lens. Alternatively, constructing the exit lens  710  as a compound lens, as opposed to a singlet, allows more design freedom to optimize the optics while preserving the main characteristics of the optical system as presented here. With reference to  FIG.  9 C , the concave surface  711  is characterized by a radius of curvature r y , while the convex surface  712  is characterized by an aspheric shape. The aspheric convex surface  712  in combination with the spherical concave surface  711  result in an exit lens  710  having varying thickness, with the outer perimeter edges  715  of the lens being thinner than the central, apex region  717  of the lens. The concave surface  711  is configured to couple to the convex surface  813  of the window  801 . In one embodiment, the exit lens  710  is formed of fused silica and has a refractive index n x  of 1.45. 
       FIGS.  10 A and  10 B  are schematic illustrations of components of the integrated surgical system of  FIGS.  7  and  8    functionally arranged to form an optical system  1010  having a first optical subsystem  1001  and a second optical subsystem  1002  that enable access to a surgical volume  720  in the irido-corneal angle. Each of  FIGS.  10 A and  10 B  include components of the focusing objective  700  and the patient interface  800  of  FIG.  9 A . However, for simplicity, the entirety of the focusing objective and the patient interface are not included in  FIGS.  10 A and  10 B . Also, for additional simplicity in  FIG.  10 A , the planar beam-folding mirror  740  of  FIGS.  9 A and  9 B  is not included and the combined laser/OCT/visual beam  701  shown in  FIG.  9 A  is unfolded or straightened out. It is understood by those skilled in the art that adding or removing planar beam folding mirrors does not alter the principal working of the optical system formed by the first optical subsystem and the second optical subsystem.  FIG.  10 C  is a schematic illustration of a beam passing through the first optical subsystem of  FIGS.  10 A and  10 B . 
     With reference to  FIG.  10 A , a first optical subsystem  1001  of the integrated surgical system  1000  includes the exit lens  710  of a focusing objective  700  and the window  801  of a patient interface  800 . The exit lens  710  and the window  801  are arranged relative to each other to define a first optical axis  705 . The first optical subsystem  1001  is configured to receive a beam, e.g., a combined laser/OCT/visual beam  701 , incident at the convex surface  712  of the exit lens  710  along a second optical axis  706 , and to direct the beam toward a surgical volume  720  in the irido-corneal angle  13  of the eye. 
     During a surgical procedure, the first optical subsystem  1001  may be assembled by interfacing the convex surface  813  of the window  801  with the concave surface  711  of the exit lens  710 . To this end, a focusing objective  700  is docked together with a patient interface  800 . As a result, the concave surface  711  of the exit lens  710  is coupled to the convex surface  813  of the window  801 . The coupling may be by direct contact or through a layer of index matching fluid. For example, when docking the patient interface  800  to focusing objective  700 , a drop of index matching fluid can be applied between the contacting surfaces to eliminate any air gap that may be between the two surfaces  711 ,  813  to thereby help pass the combined laser/OCT/visual beam  701  through the gap with minimal Fresnel reflection and distortion. 
     In order to direct the beam toward the surgical volume  720  in the irido-corneal angle  13  of the eye, the first optical subsystem  1001  is designed to account for refraction of the beam  701  as it passes through the exit lens  710 , the window  801  and the cornea  3 . To this end, and with reference to  FIG.  10 C , the refractive index n x  of the exit lens  710  and the refractive index n w  of the window  801  are selected in view of the refractive index n c  of the cornea  3  to cause appropriate beam bending through the first optical subsystem  1001  so that when the beam  701  exits the subsystem and passes through the cornea  3 , the beam path is generally aligned to fall within the irido-corneal angle  13 . 
     Continuing with reference to  FIG.  10 C  and beginning with the interface between the window  801  and the cornea  3 . Too steep of an angle of incidence at the interface where the combined laser/OCT/visual beam  701  exits the window  801  and enters the cornea  3 , i.e., at the interface between the concave surface  812  of the window and the convex surface of the cornea  3 , can create excessive refraction and distortion. To minimize refraction and distortion at this interface, in one embodiment of the first optical subsystem  1001 , the refractive index of the window  801  is closely matched to the index of the cornea  3 . For example, as describe above with reference to  FIGS.  9 A and  9 B , the window  801  may have a refractive index lower than 1.42 to closely match the cornea  3 , which has a refractive index of 1.36. 
     Excessive refraction and distortion at the interface where the combined laser/OCT/visual beam  701  exits the window  801  and enters the cornea  3  may be further compensated for by controlling the bending of the beam  701  as it passed through the exit lens  710  and the window  801 . To this end, in one embodiment of the first optical subsystem  1001  the index of refraction n w  of the window  801  is larger than each of the index of refraction n x  of the exit lens  710  and the index of refraction n c  of the cornea  3 . As a result, at the interface where the combined laser/OCT/visual beam  701  exits the exit lens  710  and enters the window  801 , i.e., interface between the concave surface  711  of the exit lens and the convex surface  813  of the window, the beam passes through a refractive index change from high to low that cause the beam to bend in a first direction. Then, at the interface where the combined laser/OCT/visual beam  701  exits the window  801  and enters the cornea  3 , i.e., interface between the concave surface  812  of the exit lens and the convex surface of the cornea, the beam passes through a refractive index change from low to high that cause the beam to bend in a second direction opposite the first direction. 
     The shape of the window  801  is chosen to be a meniscus lens. As such, the incidence angle of light has similar values on both surfaces  812 ,  813  of the window  801 . The overall effect is that at the convex surface  813  the light bends away from the surface normal and at the concave surface  812  the light bends towards the surface normal. The effect is like when light passes through a plan parallel plate. Refraction on one surface of the plate is compensated by refraction on the other surface a light passing through the plate does not change its direction. Refraction at the entering, convex surface  712  of the exit lens  710  distal to the eye is minimized by setting the curvature of the entering surface such that angle of incidence β of light  701  at the entering surface is close to a surface normal  707  to the entering surface at the intersection point  708 . 
     Here, the exit lens  710 , the window  801 , and the eye  1  are arranged as an axially symmetric system with a first optical axis  705 . In practice, axial symmetry is an approximation because of manufacturing and alignment inaccuracies of the optical components, the natural deviation from symmetry of the eye and the inaccuracy of the alignment of the eye relative to the window  801  and the exit lens  710  in a clinical setting. But, for design and practical purposes the eye  1 , the window  801 , and the exit lens  710  are considered as an axially symmetric first optical subsystem  1001 . 
     With continued reference to  FIG.  10 A , a second optical subsystem  1002  is optically coupled to the first optical subsystem  1001  at an angle α relative to the first optical axis  705  of the first optical subsystem  1001 . The advantage of this arrangement is that both optical subsystems  1001 ,  1002  can be designed at a much lower numerical aperture compared to a system where all optical components are designed on axis with a common optical axis. 
     The second optical subsystem  1002  includes a relay lens  750  that, as previously described with reference to  FIG.  8   , generates a conjugate surgical volume  721  of the surgical volume  720  within the eye. The second optical subsystem  1002  includes various other components collectively indicated as an optical subsystem step  1003 . Referring to  FIG.  8   , these components may include a femtosecond laser source  200 , an OCT imaging apparatus  300 , a visual observation device  400 , beam conditioners and scanners  500 , and beam combiners  600 . 
     The second optical subsystem  1002  may include mechanical parts (not shown) configured to rotate the entire subsystem around the first optical axis  705  of the first optical subsystem  1001 . This allows optical access to the whole 360-degree circumference of the irido-corneal angle  13  of the eye  1 . 
     With reference to  FIG.  10 B , flexibility in arranging the first and second optical subsystems  1001 ,  1002 , relative to each other may be provided by an optical assembly  1004  interposed between the optical output of the second optical subsystem  1002  and the optical input of the first optical subsystem  1001 . In one embodiment, the optical assembly  1004  may include one or more planar beam-folding mirrors  740 , prisms (not shown) or optical gratings (not shown) configured to receive the optical output, e.g., combined laser/OCT/visual beam  701 , of the second optical subsystem  1002 , change or adjust the direction of the combined laser/OCT/visual beam, and direct the beam to the optical input of the first optical subsystem  1001  while preserving the angle α between the first optical axis  705  and the second optical axis  706 . 
     In another configuration, the optical assembly  1004  of planar beam-folding mirrors  740  further includes mechanical parts (not shown) configured to rotate the assembly around the first optical axis  705  of the first optical subsystem  1001  while keeping the second optical subsystem  1002  stationary. Accordingly, the second optical axis  706  of the second optical subsystem  1002  can be rotated around the first optical axis  705  of the first optical subsystem  1001 . This allows optical access to the whole 360-degree circumference of the irido-corneal angle  13  of the eye  1 . 
     With considerations described above with reference to  FIGS.  9 A,  9 B and  9 C , the design of the first optical subsystem  1001  is optimized for angled optical access at an angle α relative to the first optical axis  705  of the first optical subsystem  1001 . Optical access at the angle α compensates for optical aberrations of the first optical subsystem  1001 . Table 1 shows the result of the optimization at access angle α=72 degrees with Zemax optical design software package. This design is a practical embodiment for image guided femtosecond glaucoma surgery. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                   
                 Center 
               
               
                   
                 Structure and 
                 Refractive 
                 Radius 
                 Thickness 
               
               
                 Surface 
                 Material 
                 index 
                 [mm] 
                 [mm] 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 concave 
                 Exit lens 710 of 
                 1.45 
                 −10 
                 4.5 
               
               
                 surface 
                 focusing objective. 
                   
                   
                   
               
               
                 711, 
                 Fused silica 
                   
                   
                   
               
               
                 convex 
                   
                   
                   
                   
               
               
                 surface 
                   
                   
                   
                   
               
               
                 712 
                   
                   
                   
                   
               
               
                 concave 
                 Window 801 of 
                 1.50 
                 −10.9 
                 1.0 
               
               
                 surface 
                 patient interface. 
                   
                   
                   
               
               
                 812, 
                 BK7G18 
                   
                   
                   
               
               
                 convex 
                   
                   
                   
                   
               
               
                 surface 
                   
                   
                   
                   
               
               
                 813 
                   
                   
                   
                   
               
               
                 3 
                 Cornea 
                 1.36 
                 −7.83 
                 0.54 
               
               
                 8 
                 Aqueous humor 
                 1.32 
                 −6.53 
                 3.5 
               
               
                 Target 
                 Ophthalmic tissue 
                 1.38 
                 N/A 
                 0 to 1 mm 
               
               
                   
               
            
           
         
       
     
     This design produces diffraction limited focusing of 1030 nm wavelength laser beams and 850 nm wavelength OCT beams with numerical aperture (NA) up to 0.2. In one design, the optical aberrations of the first optical subsystem are compensated to a degree that the Strehl ratio of the first optical subsystem for a beam with numerical aperture larger than 0.15 at the irido-corneal angle is larger than 0.9. In another design, the optical aberrations of the first optical subsystem are partially compensated, the remaining uncompensated aberrations of the first optical system are compensated by the second optical subsystem to a degree that the Strehl ratio of the combined first and second optical subsystem for a beam with numerical aperture larger than 0.15 at the irido-corneal angle is larger than 0.9. 
     Calibration 
     The femtosecond laser source  200 , OCT imaging apparatus  300 , and visual observation device  400  of the integrated surgical system  1000  are first individually calibrated to ensure their internal integrity and then cross-calibrated for system integrity. The essential part of system calibration is to ensure that the when the surgical focus of a laser beam  201  is commanded to a location of a surgical volume  720 , as identified by the OCT imaging apparatus and/or the visual observation device  400 , the achieved location of the focus matches the commanded location of the focus within a certain tolerance, typically within 5 to 10 μm. Also, graphical and cursor outputs, images, overlays displayed on a user interface  110 , such as a computer monitor, and user inputs of ocular tissue surgical volume  720  locations accepted from the user interface  110  should correspond to actual locations in tissue within predetermined tolerances of similar accuracy. 
     One embodiment of this spatial calibration procedure starts with imaging calibrated scales and scaling magnifications of the OCT imaging apparatus  300  and/or the visual observation device  400  and their displays in a way that the scale value on the display matches the real scale of the calibration target. Then laser calibration patters are exposed or burned into transparent calibration targets, and the calibration patterns are subsequently imaged. Then, the intended patterns and the actual burned patterns are compared with the imaging system of the integrated surgical system  1000  or by a separate microscope. If they do not match within the specified tolerance, the scaling parameters of the surgical patterns are re-scaled by adjusting the scaling of the laser beam scanners. This procedure is iterated, if necessary, until all spatial calibrations are within tolerance. 
     Laser Surgery with Ocular Tissue Modification 
     The anatomy of the eye relevant to the surgical treatment enabled by the integrated surgical system  1000  disclosed herein is illustrated in  FIGS.  1 - 4   . To reduce the IOP, laser treatment targets ocular tissues that affect the trabecular outflow pathway  40 . These ocular tissues may include the trabecular meshwork  12 , the scleral spur  14 , the uveal  15 , the corneoscleral meshwork  16 , the juxtacanalicular tissue  17 , the Schlemm&#39;s canal  18 , the collector channels  19  within the irido-corneal angle  13 . 
     Disclosed herein is a laser pattern particularly effective in affecting the trabecular outflow pathway  40 . Since the laser interaction volume is small, on the order of a few micrometers (μm), the interaction of ocular tissue with each laser shot of a repetitive laser breaks down ocular tissue locally at the focus of the laser. Pulse duration of the laser for photo-disruptive interaction in ocular tissue can range from several femtoseconds to several nanoseconds and pulse energies from several nanojoules to tens of microjoules. The laser pulses at the focus, through multiphoton processes, breaks down chemical bonds in the molecules, locally photo-dissociate tissue material and create gas bubbles in wet tissue. The breakdown of tissue material and mechanical stress from bubble formation fragments the tissue and create clean continuous cuts when the laser pulses are laid down in proximity to one another along geometrical lines and surfaces. 
     For the sake of the following description the basic interaction volumes are referred to as cells. The size of a cell is determined by the extent of the influence of the laser-tissue interaction. When the laser spots, or cells, are spaced close along a line, the laser creates a narrow, microscopic channel. A wider channel can be created by closely spacing a multitude of laser spots within the cross section of the channel. For example, a cylindrical channel can be created by first calculating the coordinates of the overall position and size of the cylinder. Then, using the size of the cells as a parameter, calculate the coordinates of each cell in a closely packed cell arrangement within the volume of the cylinder. The arrangement of the cells resembles the arrangement of atoms in a crystal structure. 
     The easiest is to calculate a cubic cell structure, in this case the individual cells are arranged in regularly spaced rows, columns and sheets, and the coordinates of the cells can be calculated sequentially from neighbor to neighbor in the order of rows columns and sheets. The laser scanner hardware can also follow this regular sequence to scan the laser beam without excessive jumps. Channels can be created with different cross sections, with oval, rectangular, square or other regular or irregular cross sections. A channel cut in the ocular tissue can conduct aqueous humor  8 , its conductivity increasing with the cross-sectional area of the channel. 
       FIGS.  11 A and  11 B  illustrate sectional views of the irido-corneal angle where the surgical laser scans to affect a surgical volume  900  ( FIG.  11 A ) to form a channel opening  920  ( FIG.  11 B ). The surgical volume  900  in the trabecular meshwork, extends from the anterior chamber  7  and through the inner wall of the Schlemm&#39;s canal  18 . Laser scanning modifies the ocular tissue in the surgical volume  900  to create a channel opening  920 . The channel opening  920  reduces the flow resistance in the ocular tissue to increase aqueous flow from the anterior chamber  7  into the Schlemm&#39;s canal  18  and thereby reduce the IOP of the eye. The size of the channel opening  920  will determine the reduction of the outflow pathway resistance and the longevity of effectiveness. 
     Image guidance is essential for this procedure to locate the structures precisely and to monitor the success of the treatment. Minimizing the size and volume of the treated ocular tissue also helps minimize the amount of gas created and gas-induced tissue movements. As the tissue expands with the expanding gas, sudden tissue movements can occur when gas escapes from a closed volume and the gas filled void collapses. Such sudden tissue movements can create discontinuities in the surgical incisions and should be avoided or minimized. 
     Another consideration for creating surgical patterns in the ocular tissue is the potential shadow effect of the gas bubbles as the incision progresses. In general, the incision progresses should proceed from a location further from the laser and progress towards a location closer to the laser to minimize the shadow effect. The amount of gas is also less when the laser is focused tightly to a diffraction limited focal spot and the threshold pulse energy for photo-disruption interaction is lowered. When the laser is operated at low threshold, the size of local interaction volume and the size of the gas bubbles are smaller. This means that the cells filling the surgical volume should be spaced closer. 
     Table 2 displays surgical laser and treatment pattern parameters for several incisions of different sizes. The range of the parameter set is limited by the Maximum Permissible Exposure (MPE) limit of laser light entering the eye and practical ranges for the repetition rate of the laser and the scanning speed of the scanners. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                 Channel size 
                 Channel 
                 Cell size 
                 Laser 
                 Laser 
                 Laser 
                   
               
               
                   
                 x[mm], 
                 cross 
                 x[μm], 
                 average 
                 repetition 
                 pulse 
                 Procedure 
               
               
                 Tissue 
                 y[mm], 
                 section 
                 y[μm], 
                 power 
                 rate 
                 energy 
                 time 
               
               
                 treated 
                 z[mm] 
                 [mm 2 ] 
                 z[μm] 
                 [W] 
                 [kHz] 
                 [μJ] 
                 [s] 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Trabecular 
                 1.5, 0.2, 0.2 
                 0.3 
                 3, 3, 3 
                 0.9 
                 300 
                 3 
                 7.4 
               
               
                 meshwork 
               
               
                 Trabecular 
                 2, 0.2, 0.2 
                 0.4 
                 4, 4, 4 
                 1 
                 200 
                 5 
                 6.3 
               
               
                 meshwork 
               
               
                   
               
            
           
         
       
     
     With respect to MPE, the angled beam path  30  of  FIG.  6    is the most advantageous since light beams from the femtosecond laser source  200  or the OCT imaging apparatus  300  transmitted through the tissue do not directly reach the retina. This is in contrast with known corneal and cataract surgeries, where direct laser light or OCT light transmitted through the tissue reaches the retina. Therefore, the angled beam path  30  of  FIG.  6    can use higher beam average power. Higher average power for the surgical laser results in faster procedure time. Higher average power for the OCT beam results in faster OCT image acquisition time for the same image quality or better image quality for the same image acquisition time. With respect to cell size and laser pulse energy, smaller cell sizes and pulse energies are preferred to minimize the amount of gas created in the tissue. 
     Linear perfusion models, experimental (Liu et al., 2005) and clinical findings from ELT procedures indicate channel cross sections from 0.24 mm 2  to 0.4 mm 2  can achieve sufficient IOP reduction. As seen from Table 2, the surgical laser procedure enabled by the integrated surgical system disclosed herein can produce similar channel cross sections to those in Liu et al. and can be completed in less than 10 seconds. 
       FIG.  12    is a flowchart of a method of reducing intraocular pressure in an eye having a cornea, an anterior chamber, and an irido-corneal angle comprising an aqueous humor outflow pathway formed of a trabecular meshwork, a Schlemm&#39;s canal, and one or more collector channels branching from the Schlemm&#39;s canal, the method comprising. The method may be performed by the integrated surgical system  1000  of  FIGS.  7 - 10 B . 
     At step  1202 , an OCT beam  301  is delivered through the cornea  3  and the anterior chamber  7  into the irido-corneal angle  13 . In one embodiment, the OCT beam  301  has a resolution less than or equal to approximately 5 micrometers and is delivered to the irido-corneal angle  13  by directing the OCT beam to a first optical subsystem  1001  that includes a window  801  coupled to the cornea  3  and an exit lens  710  coupled to the window. 
     At step  1204 , an OCT image of a portion of the irido-corneal angle  13  is acquired based on the OCT beam  301  delivered to the irido-corneal angle through the first optical subsystem  1001 . To this end, an OCT return beam  301  is received through the first optical subsystem  1001  and processed at an OCT imaging apparatus  300  using known OCT imaging techniques. 
     At step  1206 , a surgical volume  900  of ocular tissue to be modified is determined based on the OCT image. The surgical volume  900  may be determined based on a 2D cross-sectional OCT image that is displayed on a control system  100  of the integrated surgical system  1000 . A visual observation beam  401  may also be used to determine the surgical volume  900 . To this end, a visual observation beam  401  may be acquired from the irido-corneal angle  13  by a microscope  400  through the first optical subsystem  1001 , and the volume  900  of ocular tissue to modify may be determined by presenting the OCT image and visual observation signal overlaid on a display screen of the control system  100 . Alternatively, the OCT image and visual observation signal may be registered on a display screen. 
     In one embodiment, the Schlemm&#39;s canal  18  is characterized by a circumference, and the surgical volume  900  of ocular tissue to modify is determined based on the density of collector channels  19  around the circumference. In this case, a density distribution of collector channels  19  around at least a portion of the circumference of the Schlemm&#39;s canal  18  is determined based on OCT images. A region of the Schlemm&#39;s canal  18  having a density above a threshold criterion is identified, and the proximity of the identified region is included in the volume of ocular tissue to modify. The criterion may be the 50 th  percentile of the distribution, the 75 th  percentile, or a numerical value higher than the 75 th  percentile. In another embodiment, the volume  900  of ocular tissue to be modified is in the proximity of one or more of the collector channels  19 . 
     At step  1208 , each of an OCT beam  301  and a laser beam  201  is delivered through the cornea  3 , and the anterior chamber  7  into the irido-corneal angle  13 . In one embodiment, the OCT beam  301  and laser beam  201  have substantially equal resolutions, e.g., less than or equal to approximately 5 micrometers, and each beam is delivered to the irido-corneal angle by directing each beam to a first optical subsystem  1001  that includes a window  801  coupled to the cornea  3  and an exit lens  710  coupled to the window. The OCT beam  301  and the laser beam  201  may be collinearly directed to the first optical subsystem  1001  along a same optical path, for example by multiplexing the beams. Alternatively, the OCT beam  301  and the laser beam  201  may be non-collinearly directed to the first optical subsystem at the same time along spatially separated or angled optical paths. 
     Distortion and aberrations of the beams  201 ,  301  caused by oblique angle entry into the eye are compensated for by directing each beam into the first optical subsystem  1001  at an angle. To this end, the eye  1  includes a direction of view and the first optical subsystem  1001  is positioned relative to the eye so as to include a first optical axis  705  that is substantially aligned with the direction of view of the eye. The beams  201 ,  301  are input to the first optical subsystem  1001  by directing each beam into a convex surface  713  of the exit lens  710  along a second optical axis  706  offset from the first optical axis  705  by an angle α. Additionally, each beam  201 ,  301  may be directed into the convex surface  713  of the exit lens  710  at an angle β relative to a surface normal  707  to the convex surface. 
     At step  1210 , a volume  900  of ocular tissue within the trabecular outflow pathway  40  is modified to reduce a pathway resistance present in one or more of the trabecular meshwork  12 , the Schlemm&#39;s canal  18 , and the one or more collector channels  19  by applying the laser beam  201  to ocular tissue defining the volume. To this end, a laser beam  201  having a wavelength between 330 nanometers and 2000 nanometers may be scanned in multiple directions to interact with the ocular tissue defining the surgical volume  900 . The laser beam  201  may be applied in a continuous manner or as a multitude of laser pulses with a pulse duration between 20 femtoseconds and 1 nanosecond. The laser beam  201  causes photo-disruptive interaction with the ocular tissue to reduce the pathway resistance or create a new outflow pathway  40 . In one embodiment, photo-disruptive interaction with the ocular tissue creates a channel opening  902  opened through the trabecular meshwork connecting the anterior chamber and the Schlemm&#39;s canal. 
     Accessing the Irido-Corneal Angle 
       FIG.  13    is a flowchart of a method of directing a light beam to an irido-corneal angle of an eye having a direction of view and a cornea with a refractive index n c . The method may be performed by the integrated surgical system  1000  of  FIGS.  7 - 10 B . 
     At step  1302 , a first optical subsystem  1001  and a second optical subsystem  1002  are arranged relative to each other. The first optical subsystem  1001  includes a window  801  formed of a material with a refractive index n w . The window  801  has a concave surface  812  and a convex surface  813  opposite the concave surface. The first optical subsystem  1001  also includes and an exit lens  710  formed of a material having a refractive index n x . The exit lens  710  has a concave surface  711  and a convex surface  712  opposite the concave surface. The concave surface  711  of the exit lens  710  is configured to couple to the convex surface  813  of the window  801  to define a first optical axis  705  extending through the window and the exit lens. The concave surface  812  of the window  801  is configured to detachably couple to the cornea  3  of the eye such that the first optical axis  705  is generally aligned with the direction of view of the eye. 
     At step  1304 , a light beam output by the second optical subsystem  1002  is directed to be incident at the convex surface  712  of the exit lens  710  along a second optical axis  706  at an angle α that is offset from the first optical axis  705 . To this end, the second optical subsystem  1002  or another intermediate optical assembly  1004  may be configured to determine a measure of angle separation between the first optical axis and the second optical axis, and to adjust the orientation of the second optical axis until the angle of separation is at angle α. The angle α is typically greater than 30 degrees. More specifically, the angle α may be between 60 degrees and 80 degrees. Even more specifically, the angle α is approximately 72 degrees. 
     At step  1306 , the light beam output by the second optical subsystem  1002  may be also directed to intersect the convex surface  712  of the exit lens  710  at an intersection point and an angle θ between the second optical axis  706  and a surface normal  707  to the convex surface of the exit lens. Again, the second optical subsystem  1002  or another intermediate optical assembly  1004  may be configured to determine a measure of angle separation between the second optical axis and the surface normal  707 , and to adjust the orientation of the second optical axis until the angle of separation is at angle β. 
     In some arrangements, as shown for example in  FIG.  10 B , the second optical subsystem  1002  may be configured to be arrange relative to the first optical subsystem  1001  so that the light beam  701  is output by the second optical subsystem along an axis offset from the second optical axis  706 . In these cases, in the directing process of step  1304 , the light beam  701  is received at an optical assembly  1004  interposed between the first optical subsystem  1001  and the second optical subsystem  1002  and redirected into general alignment with the second optical axis  706 . The second optical axis  706  may be rotated around the first optical axis  705  while maintaining the second optical axis offset from the first optical axis by an angle substantially equal to the angle α. Doing so allows for treatment around the circumference of the irido-corneal angle  13 . In configurations where the second optical axis  706  intersects the convex surface  712  of the exit lens  710  at an intersection point  708  and at an angle β between the second optical axis and a surface normal  707  to the convex surface of the exit lens, the directing process of step  1306  involves rotating the second optical axis around the first optical axis while also maintaining an angle between the second optical axis and the surface normal that is substantially equal to the angle β. 
     Minimally Invasive and Non-Invasive Surgical Treatments 
     Surgical treatments disclosed below reduce outflow pathway resistance while minimizing ocular tissue modification through careful design and selection of laser treatment patterns. As used herein a treatment pattern defines a three-dimensional model of ocular tissue to be modified by a laser or a three-dimensional model of ocular fluid to be affected by a laser. A treatment pattern is typically defined by a set of surgical parameters. The surgical parameters may include one or more of a treatment area A that represents a surface area of ocular tissue through which the laser will travel and a treatment thickness t that represents the level to which the laser will cut into the ocular tissue or the level at which the laser will affect ocular fluid. Thus, a laser applied in accordance with a treatment pattern may affect or produce a surgical volume that resembles the three-dimensional model of the treatment pattern, or may affect fluid located in an interior of an eye structure resembled by the three-dimensional model. 
     Additional surgical parameters define the placement of the surgical volume or affected volume within the eye. Placement parameters may include one or more of a location l that represents where the treatment is to occur relative to the circumferential angle of the eye, and a treatment depth d that represents a position of the three-dimensional model of ocular tissue or ocular fluid within the eye relative to a reference eye structure. In the following, the treatment depth d is shown and described relative to the region where the anterior chamber  7  meets the trabecular meshwork  12 . Together, the treatment pattern and the placement parameters define a treatment plan. 
     Minimizing or eliminating the invasiveness of the surgical treatment procedure is beneficial for multiple reasons. First, non-invasive treatments and minimally invasive treatments minimize damage to healthy ocular tissue and thereby preserve the filtering function of untreated parts of the trabecular meshwork tissue. Second, by preserving the mechanical structural integrity of the trabecular meshwork tissue as much as possible, the potential for the collapse and closure of the existing or newly created outflow pathway is minimized. Third, the disclosed laser treatment patterns give more control over the amount of IOP reduction. Achieving the right IOP is important for the clinical outcome. Too small of an IOP reduction diminishes the effectiveness of glaucoma treatment, while too large of an IOP reduction may cause deflation of the eye. Finally, minimizing the volume of laser treated ocular tissue results in faster procedure time and reduces the chance of unintended tissue movement during the procedure. 
     Minimally Invasive Laser Surgery 
     As described above, a femtosecond laser provides highly localized, non-thermal photo-disruptive laser-tissue interaction with minimal collateral damage to surrounding ocular tissue. Photo-disruptive interaction of the laser is utilized in optically transparent tissue. The principal mechanism of laser energy deposition into the ocular tissue is not by absorption but by a highly nonlinear multiphoton process. This process is effective only at the focus of the pulsed laser where the peak intensity is high. Regions where the beam is traversed but not at the focus are not affected by the laser. Therefore, the interaction region with the ocular tissue is highly localized both transversally and axially along the laser beam. 
     Applying the foregoing femtosecond laser capabilities, an embodiment of the integrated surgical system  1000 , reduces outflow pathway resistance using one or more laser treatment patterns to modify ocular tissue in a localized manner. Referring to  FIG.  3   , as previously described, the trabecular meshwork  12  has three layers, the uveal  15 , the corneoscleral meshwork  16 , and the juxtacanalicular tissue  17 . These layers are porous and permeable to aqueous, with the uveal  15  being the most porous and permeable, followed by the corneoscleral meshwork  16 . The least porous and least permeable layer of the trabecular meshwork  12  is the juxtacanalicular tissue  17 . The inner wall  18   a  of the Schlemm&#39;s canal  18 , which is also porous and permeable to aqueous, has characteristics similar to the juxtacanalicular tissue  17 . Based on this knowledge, various treatment patterns that 1) select one or more layers of the trabecular meshwork  12  for modification and 2) control the extent of such modifications, may be designed. These treatment patterns are defined by a set of surgical parameters, which in turn, define the geometrical dimensions of ocular tissue modifications (or surgical cuts) that result from laser surgery. Examples of different treatment patterns follow. 
     In one example, with reference to  FIGS.  11 A,  11 B, and  11 C , which illustrate sectional views and a perspective view of the irido-corneal angle  13 , a surgical laser  701  may scan ocular tissue in accordance with a first treatment pattern P 1  designed to affect a surgical volume  900  (shown in two and three dimensions in  FIG.  11 A ) to form a contiguous, wide and deep channel opening  920  (shown in two dimensions in  FIG.  11 B  and three dimensions in  FIG.  11 C ). The deep channel opening  920  extends from the anterior chamber  7 , through each of the uveal  15 , the corneoscleral meshwork  16 , the juxtacanalicular tissue  17  of the trabecular meshwork  12 , and the inner wall  18   a  of the Schlemm&#39;s canal  18 . The deep channel opening, and other channel opening disclosed herein, may be a single lumen defining a fluid pathway or an arrangement of adjacent pores forming a sponge like structure defining a fluid pathway or a combination thereof. 
     The movement of the laser as it scans to affect the surgical volume  900  follows the first treatment pattern P 1 , which is defined by a set of surgical parameters that include a treatment area A and a thickness t. The treatment area A is defined by a width w and a height h. The width may be defined in terms of a measure around the circumferential angle. For example, the width w may be defined in terms of an angle, e.g., 90 degrees, around the circumferential angle. 
     An initial placement of the laser focus within the eye is defined by a set of placement parameters, including a depth d (not shown) and a location l (not shown). The location l defines a point around the circumferential angle of the eye at which laser treatment will begin, while the depth d defines a point between the anterior chamber  7  and the Schlemm&#39;s canal  18  where the treatment begins or ends. 
     The channel opening  920  ( FIGS.  11 B and  11 C ) resulting from laser application of the first treatment pattern P 1  resembles the surgical volume  900  and is characterized by an area A and thickness t similar to those of the surgical volume and the treatment pattern. The depth dis essentially null, thus placing an end of the surgical volume  900  at the region where the anterior chamber  7  meets the trabecular meshwork  12 . The thickness t of the resulting deep channel opening  920  extends from the anterior chamber  7  and through the inner wall  18   a  of the Schlemm&#39;s canal  18 , while the area A is such that the resulting channel opening  920  ( FIGS.  11 B and  11 C ) is characterized by a single opening. 
     In the example of  FIGS.  11 B and  11 C , the channel opening  920  has a first end in fluid communication with the Schlemm&#39;s canal  18  and a second end in fluid communication with the anterior chamber  7 . The fluid communication may be enabled through a one or more lumens forming a pathway through the channel opening  920  and/or an arrangement of pores forming a porous pathway through the channel opening. 
     In another example, with reference to  FIGS.  14 A,  14 B, and  14 C , which illustrate sectional views and a perspective view of the irido-corneal angle  13 , a surgical laser may scan ocular tissue in accordance with a second treatment pattern P 2  designed to affect a surgical volume  901  (shown in two and three dimensions in  FIG.  14 A ) to form a single, wide and shallow channel opening  921  (shown in two dimensions in  FIG.  14 B  and three dimensions in  FIG.  14 C ). The shallow channel opening  921  extends from the Schlemm&#39;s canal  18 , through the inner wall  18   a  of the Schlemm&#39;s canal  18  and partially through the trabecular meshwork  12 , so that only a portion of the tissue between the anterior chamber  7  and the Schlemm&#39;s canal is treated. In the example of  FIGS.  14 A,  14 B, and  14 C , the shallow channel opening  921  extends through the juxtacanalicular tissue  17  and partially into the corneoscleral meshwork  16 . In other treatment patterns, the shallow channel opening  921  may extend through the corneoscleral meshwork  16  and partially into the uveal  15 . 
     In either case, the movement of the laser as it scans to affect the surgical volume  901  follows the second treatment pattern P 2 , which is defined by a set of surgical parameters that include a treatment area A and a thickness d. The treatment area A is defined by a width w and a height h. Again, the width may be defined in terms of a measure around the circumferential angle. For example, the width w may be defined in terms of an angle, e.g., 90 degrees around the circumferential angle. 
     An initial placement of the laser focus within the eye is defined by a set of placement parameters, including a depth d and a location l (not shown). The location l defines a point around the circumferential angle of the eye at which laser treatment will begin, while the depth d defines a point between the anterior chamber  7  and the Schlemm&#39;s canal  18  where the treatment begins or ends. 
     The channel opening  921  ( FIGS.  14 B and  14 C ) resulting from laser application of the second treatment pattern P 2  resembles the surgical volume  902  and is characterized by an area A and thickness t similar to those of the surgical volume and the treatment pattern. The depth d places an end of the surgical volume  902  in the corneoscleral meshwork  16 . The thickness t of the resulting shallow channel opening  921  extends from the Schlemm&#39;s canal  18 , through the inner wall  18   a  of the Schlemm&#39;s canal and only partially into the trabecular meshwork  12 , while the area A is such that the resulting shallow channel opening  921  ( FIGS.  14 B and  14 C ) is characterized by a single opening. 
     In this example, the channel opening  921  has a first end in fluid communication with the Schlemm&#39;s canal  18  and a second end that terminates in a layer of ocular tissue between the anterior chamber  7  and the wall of the Schlemm&#39;s canal  18 . The fluid communication may be enabled through a one or more lumens forming a pathway through the channel opening  921  and/or an arrangement of pores forming a porous pathway through the channel opening. In other configuration, the channel opening  921  may have a first end in fluid communication with the anterior chamber  7  and a second end that terminates in a layer of ocular tissue between the anterior chamber and the wall of the Schlemm&#39;s canal  18 . 
     In yet another example, with reference to  FIGS.  15 A,  15 B, and  15 C , which illustrate sectional views and a perspective view of the irido-corneal angle  13 , a surgical laser may scan ocular tissue in accordance with a third treatment pattern P 3  designed to affect an array of individual surgical volumes  903  (shown in two and three dimensions in  FIG.  15 A ) to form a corresponding array of shallow sub-openings  923  (shown in two dimensions in  FIG.  15 B  and three dimensions in  FIG.  15 C ). Each of the shallow sub-openings  923  extends from the Schlemm&#39;s canal  18 , through the inner wall  18   a  of the Schlemm&#39;s canal  18  and partially through the trabecular meshwork  12 , so that only a portion of the tissue between the anterior chamber  7  and the Schlemm&#39;s canal is treated. The array of shallow sub-openings  923  collectively forming a sieve structure. In the example of  FIGS.  15 A,  15 B, and  15 C , the sub-openings  923  extend through the juxtacanalicular tissue  17  and partially into the corneoscleral meshwork  16 . In other treatment patterns, the sub-openings  923  may extend through the corneoscleral meshwork  16  and partially into the uveal  15 . 
     In either case, the movement of the laser as it scans to affect the array of individual surgical volumes  903  follows the third treatment pattern P 3 , which is defined by a set of surgical parameters that include a treatment area A and a thickness d. The treatment area A is defined by a width w and a height h and establishes an overall boundary within which lies an array of individual sub-treatment areas. The width w may be defined in terms of a measure around the circumferential angle. For example, the width w may be defined in terms of an angle, e.g., 90 degrees around the circumferential angle. 
     An initial placement of the laser focus within the eye is defined by a set of placement parameters, including a depth d and a location l (not shown). The location l defines a point around the circumferential angle of the eye at which laser treatment will begin, while the depth d defines a point between the anterior chamber  7  and the Schlemm&#39;s canal  18  where the treatment begins or ends. 
     Each sub-treatment area within the treatment area A is characterized by a cross-section defined by a geometric shape, e.g., rectangular, square, round. The individual shallow sub-openings  923  ( FIGS.  15 B and  15 C ) resulting from laser application of the third treatment pattern P 3  resembles the individual surgical volumes  903  and is characterized by sub-area A S  and thickness t similar to those of the surgical volume and the treatment pattern. The depth d places an end of the individual surgical volumes  903  in the corneoscleral meshwork  16 . The thickness t of the resulting individual shallow sub-openings  923  extends from the Schlemm&#39;s canal  18 , through the inner wall  18   a  of the Schlemm&#39;s canal and only partially into the trabecular meshwork  12 . 
     Different levels of aqueous flow conductivity between the anterior chamber  7  and the Schlemm&#39;s canal  18  may be obtained using different laser treatment patterns having different surgical parameter sets. For example, flow conductivity typically increases monotonically together with increases in one or more of treatment area A and thickness d. The dependence between overall flow conductivity and treatment patterns and surgical parameter sets can be found by modeling, empirically through clinical studies, successive approximation, or by a combination of these techniques. An example of modeling of treatment patterns is described later below in the Aqueous Flow Model section. 
     Non-Invasive Laser Surgery—Photodisruptive Laser Pneumatic Canaloplasty 
     Applying the foregoing femtosecond laser capabilities, another embodiment of the integrated surgical system  1000  improves outflow pathway conductivity through pneumatic expansion of the Schlemm&#39;s canal  18 . Laser interaction with ocular tissue results in the formation of microscopic gas bubbles. The combined effect from multiple microscopic gas bubbles is a creation of excess gas and associated pressure in a macroscopic volume. The excess gas and associated excess pressure can propagate to regions of tissue relatively far from the location of the laser interaction. For example, excess gas can travel through porous ocular tissue into and along the Schlemm&#39;s canal  18 , and along the collector channels  19 . The excess pressure associated with the gas results in a pneumatic expansion of the ocular tissues of the aqueous outflow pathways, the Schlemm&#39;s canal  18 , and the collector channels  19 . 
     This pneumatic expansion may be utilized to open collapsed regions of the Schlemm&#39;s canal  18  and collector channels  19  and in general increase outflow for an IOP reducing effect. In this embodiment, the integrated surgical system  1000  directs and focuses the laser at the fluid inside the Schlemm&#39;s canal  18  or the collector channels  19  or in the voids of porous tissue without direct laser effect to the ocular tissue. An increase in aqueous outflow conductivity is achieved only through pneumatic expansion of the Schlemm&#39;s canal  18  and/or the collector channels  19  and ocular tissue without laser modification of ocular tissue. Importantly, avoidance of direct tissue damage by the laser minimizes healing responses and scar formation that would otherwise be invoked by laser-damaged tissue. In the absence of such scarring, the possibility of re-closure of the outflow pathways through the pneumatic expanded structures and tissue is avoided. 
       FIGS.  16 A and  16 B  illustrate before-and-after sectional views of the irido-corneal angle, where a surgical laser beam  701  is directed to the interior of a partially collapses Schlemm&#39;s canal  18  (shown in  FIG.  16 A ) to affect pneumatic expansion of the Schlemm&#39;s canal  18  (shown in  FIG.  16 B ). In this case, the treatment pattern P 4  may be defined by a treatment area A generally corresponding to a cross-sectional area of the Schlemm&#39;s canal  18  and a width w defined in terms of a measure around the circumferential angle. For example, the width w may be defined in terms of an angle, e.g., 90 degrees around the circumferential angle. The area A and width w of the treatment pattern P 4  define a volume generally corresponding to an interior of the Schlemm&#39;s canal  18 . 
     An initial placement of the laser focus within the eye is defined by a set of placement parameters, including a depth d and a location l (not shown). The location l defines a point around the circumferential angle of the eye at which laser treatment will begin, while the depth d positions the point of the laser focus within the Schlemm&#39;s canal  18 . In an embodiment, one or more locations of the Schlemm&#39;s canal spaced apart around the circumferential angle may be selected for laser application. The locations may be selected based on images of the Schlemm&#39;s canal  18 . 
     In one configuration, images of the Schlemm&#39;s canal  18  at a plurality of locations around at least a portion of the circumferential angle are obtained using, for example, OCT. Each of the images is processed to determine a measure of an anatomical feature of the Schlemm&#39;s canal  18 . Such anatomical feature may be a cross-section of the Schlemm&#39;s canal  18  and the measures may correspond to a radius, diameter, or circumference of the canal. The images are evaluated relative to a threshold measure to determine if the location associated with the image should be designated for laser delivery. In one embodiment, the threshold measure is the radius, diameter, or circumference of a Schlemm&#39;s canal  18  that is indicative of an at least partially collapsed canal. If the corresponding measure derived from the patient&#39;s image is less than the threshold measure, the location from which the image was obtained is designated a location for laser beam delivery. The threshold measure may be a predetermined value derived from a clinical database of measures from patients similar to the patient being treated. The threshold measure may also be derived through an analysis of all images collected for the patient. For example, the threshold measure may correspond to the largest measure determined from the images of the patient&#39;s Schlemm&#39;s canal, or the average of the measures determined from the images of the patient&#39;s Schlemm&#39;s canal. 
     During treatment, microscopic gas bubbles created by the laser beam  701  coalesce to form larger volumes gas bubbles  930 . As this bubble expands, it expands the Schlemm&#39;s canal  18  and the surrounding tissue. The gas bubbles  930  will dissolve in a few minutes in the fluids of the tissue, leaving the expanded Schlemm&#39;s canal behind with no gas and tissue fragments in it. The treatment is non-invasive and it can be repeated to obtain incremental reductions in IOP until a desired overall IOP reduction is achieved, all without the longer term decrease of treatment efficacy that often results from treatments involving tissue modification. 
     Pneumatic expansion of the Schlemm&#39;s canal  18  and/or the collector channels  19  typically results in an IOP reduction. Accordingly, in an embodiment of the integrated surgical system  1000 , expansion of the Schlemm&#39;s canal  18  and/or the collector channels  19  may be monitored and used to control laser treatment, e.g., stop treatment when an acceptable expansion has been achieved or when a maximum allowable pneumatic expansion is reached. The maximum allowable pneumatic expansion is a level of expansion at or above which ocular tissue and structures may be damaged. 
     For example, in one configuration, the integrated surgical system  1000  may provide images of the Schlemm&#39;s canal  18  from which changes in expansion may be observed. To this end, one or both of the OCT imaging apparatus  300  and visual observation device  400  may continually output current cross-sectional OCT images or visual images of the Schlemm&#39;s canal  18  for display on a screen during laser treatment. The operating surgeon may observe these images during the treatment, and determine to stop the laser treatment when the images indicate that a cross-section dimension, e.g., diameter, radius, circumference, of the Schlemm&#39;s canal  18  has either: 1) increased relative to its preoperative size by a desirable amount, or 2) is approaching a measure corresponding to a level of expansion at or above which ocular tissue and structures may be damaged. 
     In another configuration, control of laser treatment is implemented by the integrated surgical system  1000 . To this end, a processor of the integrated surgical system  1000  executes an algorithm that continuously processes OCT cross-sectional images or visual images of the Schlemm&#39;s canal  18  during treatment to obtain measures indicative of pneumatic expansion of the canal. The measures may be a cross-section dimension, e.g., diameter, radius, circumference, of the Schlemm&#39;s canal  18 . The processor then evaluates the measures to determine if a criterion is satisfied. For example, a criterion may be a target cross-section dimension value or may be a percentage increase from a baseline cross-section dimension value. The baseline value may correspond to, for example, a preoperative cross-section dimension value. If the criterion is satisfied, e.g., the target value or the percentage increase is met, the processor stops the laser treatment. If the criterion is not satisfied, e.g., the target value or the percentage increase is not met, the processor allows the laser treatment to continue. 
     Aqueous Flow Model 
     In accordance with embodiments disclosed herein, treatment patterns for laser tissue modification may be modeled using an aqueous flow model derived from Goldmann&#39;s model. Goldmann&#39;s model (R. F. Brubaker, Experimental Eye Research 78 (2004) 633-637) describes the relation between the IOP, the aqueous flow rate and the flow resistance. The model is described by the equation: 
         F =( Pi−Pe )* C+U , where:         F is the rate of entry of the newly formed aqueous humor into the anterior chamber  7 ,   U is the rate of outflow of aqueous humor via all channels that are IOP independent, such as the uveoscleral outflow,   Pi is the IOP, defined as the pressure within the anterior chamber  7  relative to atmospheric pressure,   C is the collective hydraulic conductivity of all pressure dependent pathways out of the anterior chamber  7 , and   Pe is the extraocular pressure, i.e., a summation over a number of discrete microscopic pressure channels that drain aqueous humor.       
     This equation is essentially the Ohm&#39;s law for stationary fluid flow. In an analogy with electronics, F and U are analogous to electric currents, hydraulic pressure differentials are analogous to voltages and hydraulic conductivity is analogous to electronic conductivity, which is the inverse of electronic resistance. Goldmann&#39;s equation under a condition (Pi−Pe)*C=F−U=constant, shows that, under stationary conditions when the aqueous inflow rate F is constant, the pressure differential between the anterior chamber  7  and the outflow drain pressure (Pi−Pe) is inversely proportional to the collective hydraulic conductivity C. 
       FIG.  17    displays this dependence as a set of hyperbolas, each line corresponding to a different constant parameter F−U. Three parameters of the Goldmann&#39;s model can be measured in human patients: 1) Pi, the IOP within the anterior chamber  7 , 2) F, the rate of flow through the anterior chamber  7 , and 3) C, the collective hydraulic conductivity of all pressure dependent pathways out of the anterior chamber  7 . In addition, the main component of the extraocular pressure Pe, i.e., the episcleral venous pressure, can be estimated. This data allows a doctor to determine an aqueous flow diagnosis for a given patient, represented by a particular curve from the set of curves in  FIG.  17   . This curve can be used as a baseline for treatment. 
     The intraocular pressure Pi can be measured with tonometry. The aqueous humor flow F can be measured by fluorophotometry (See, e.g., Jones, R. F., Maurice, D. M., 1966. New methods of measuring the rate of aqueous flow in man with fluorescein. Exp. Eye Res. 5, 208-220). The collective hydraulic conductivity C or outflow facility can be measured by tonography, e.g., by the weighted tonometer technique (See, e.g., Grant, W. M., 1950. Tonographic method for measuring the facility and rate of aqueous flow in human eyes. Arch. Ophthalmol. 44, 204-214). The tonographic measurement takes approximately 4 minutes to obtain, which generally corresponds to the time necessary for the eye to stabilize after being subjected to additional pressure from the weighted tonometer. For preoperative assessment, it is important to diagnose the patient under the right conditions. Drug treatment for glaucoma reduces the aqueous inflow rate F. Therefore, the aqueous inflow rate F measurement should be taken with the patient temporarily taken off of drugs, or the flow measurement should be corrected for any effects from IOP reducing drugs. 
     Once the parameters of the Goldmann&#39;s model has been established by preoperative measurements, the (Pi−Pe) vs. C hyperbola curve can be constructed as shown on  FIG.  17   . This curve forms the basis for selection of surgical treatment pattern parameters, such as the treatment area A and the thickness d, for a desired outflow modification and IOP reduction. 
     Other studies (M. A. Johnstone; The Aqueous Outflow System as a Mechanical Pump; J Glaucoma 2004; 13:421-438) indicate evidence of tissue structures and mechanotransduction mechanisms within the trabecular meshwork  12  and the Schlemm&#39;s canal  18 , which, through tissue deformation coupled to aqueous flow, are capable of providing feedback mechanisms to regulate IOP. These control mechanisms are not fully understood yet and cannot be described with the simple Goldmann&#39;s model. A combined model can include a controlled portion of the aqueous flow added to the Goldmann&#39;s model. 
     With reference to  FIG.  18   , developing the electronics analogy further, a circuit diagram can be constructed for the aqueous flow. The circuit diagram may be described in terms of rows and columns, where each row is presented by like types of circuit components, e.g., Ru1+Ru2 . . . +Run, Rsc1+Rsc2 . . . +Rscn, etc., and each columns by one of every type of circuit component, e.g., Ru1+Rsc1+Rj1+Rs1+Rc1. In this diagram, constant current sources with currents F and U, respectively represent the aqueous inflow rate F and the pressure independent part of the aqueous outflow U. The inflow current F is split to three paths, Uc, U and T. These four components are defined by the following equation: 
         T=F−U−Uc , where         F is the rate of entry of the newly formed aqueous humor into the anterior chamber  7  (F from Goldmann&#39;s equation)   U is the rate of outflow of aqueous humor via all channels that are IOP independent, such as the uveoscleral outflow (U from Goldmann&#39;s equation)   Uc is the portion  1400  of the trabecular outflow, which is controlled by feedback mechanisms of the eye, and   T is the trabecular flow current, represented in  FIG.  18    by a current meter test point  1401 .       
     With reference to  FIG.  4   , T is represented by graphical arrow  40  and U is represented by arrow  42 . This representation on  FIG.  4    is schematic, since in the Goldmann&#39;s model U represents all pressure independent outflow channels, not just the uveoscleral outflow  42 . Several clinical studies indicate that the amount of the pressure independent flow U is approximately 10 percent of the aqueous inflow rate F. Nevertheless, U and T are also labeled in  FIG.  18    with callouts  42  and  40 . On the circuit diagram the lower equipotential line  7  represents the IOP Pi, while the higher equipotential line  31  represents the extraocular pressure Pe. A voltage source  1402 , represents a constant voltage source maintaining the potential difference Pi−Pe. Resistors represent the inverse of hydraulic conductivities of tissue. 
     With regards to the biomechanical properties, the ocular tissue is continuous.  FIG.  18    is a discretized model of the continuous tissue media. The volume of tissue is divided into small segments, labeled with an index i, i=1 . . . n. If the segments are sufficiently small, the discrete representations accurately describe the continuous properties of the media. For example, in the case where n=360, the circuit diagram may represent the entirety of the circumferential angle, where each segment indexed from i=1 to 360 corresponds to a one-degree segment of the 360 degree circumferential angle. Tissue division and indexing can further include division along other geometrical dimensions. Finite element modeling software such as ANSYS from Ansys Inc., Canonsburg, Pa. or COMSOL from COMSOL Inc., Burlington, Mass. can routinely handle this type of modeling and the solution of the corresponding equations. The resistors Ru, Rcs and Rj respectively represent the three sub-layers of the trabecular meshwork  12 : the uveal  15 , the corneoscleral meshwork  16  and the juxtacanalicular tissue  17 . Resistors Rsi represent the Schlemm&#39;s canal  18 . Note that Rs1 and Rsn are connected by a line, indicating that the Rsi resistors form a circle, thus modeling the circular shape of the Schlemm&#39;s canal  18 . Resistors Rc represent the collector channels  19 . 
     Precise Control of IOP with Surgery 
     With reference to  FIGS.  19 A,  19 B, and  19 C , different treatment patterns may be modeled using the circuit diagram of  FIG.  18   . For example, the treatment pattern P 1  resulting in the deep channel opening  920  shown in  FIG.  11 B  may be modeled by changing the values of the resistors Ru, Rcs and Rj (corresponding respectively to the uveal  15 , the corneoscleral meshwork  16  and the juxtacanalicular tissue  17 ) to zero in the area  920  shown in  FIG.  19 A . In the circuit model, the area  920  may be described as being two columns wide and three rows deep, where the number of columns defines the width w of the treatment pattern, and the number of rows defines the thickness t of the treatment pattern. 
     The treatment pattern P 2  resulting in the shallow channel opening  921  shown in  FIG.  14 B  may be modeled by changing the values of the resistors Rj (corresponding to the juxtacanalicular tissue  17 ) to zero in the area  921  shown in  FIG.  19 B . In the circuit model, the area  921  may be described as being two columns wide and one row deep, where the number of columns defines the width w of the treatment pattern, and the number of rows defines the thickness t of the treatment pattern. 
     The treatment pattern P 4  resulting in the pneumatic expansion  930  of the Schlemm&#39;s canal  18  shown in  FIG.  16 B  may be modeled by reducing the value of the resistors Rs (corresponding to the Schlemm&#39;s canal  18 ) to zero in the area  931  shown in  FIG.  19 C . In the circuit model, the area  931  may be described as being two columns wide and one row deep, where the number of columns defines the width w of the treatment pattern, and the number of rows defines the thickness t of the treatment pattern. 
     Patterns with other geometric shapes can be modeled in the circuit diagram and through finite element analysis in a similar manner. 
     In embodiments disclosed herein, an initial treatment pattern characterized by a set of surgical parameters that define the size and shape of tissue modifications (or surgical cuts) for a desired change in aqueous outflow is determined. Laser treatment in accordance with the initial treatment pattern is delivered and the clinical outcome is determined. If the clinical outcome is acceptable, the treatment is ended; otherwise a subsequent treatment pattern is determined and laser treatment is repeated. 
       FIG.  21    is a flowchart of a method of designing a treatment pattern using the aqueous flow model of  FIG.  18   . The method may be performed by one or more components of the integrated surgical system  1000  of  FIGS.  7 - 10 B . For example, the control system  100  may include a processor and a memory coupled to the processor that stores instructions that enable the processor to execute or implement the method of  FIG.  21   . The method of  FIG.  21    may also be performed by a processor and memory that are separate from the integrated surgical system  1000 . 
     At step  1500 , preoperative outflow parameters of the eye to be treated are obtained or derived. These measures include preoperative measures of: 1) the IOP within the anterior chamber, 2) the collective hydraulic conductivity C, and 3) the flow resistance of the Schlemm&#39;s canal Rs. The IOP can be obtained using known techniques. The collective hydraulic conductivity C may be determined from preoperative IOP measurements and weighted tonometry. The flow resistance of the Schlemm&#39;s canal Rs may be determined by measuring the canal&#39;s cross-section with the OCT imaging apparatus  300  and applying the hydrodynamic flow equation for laminar flow of the aqueous within the canal. For a Schlemm&#39;s canal  18  assumed to have a circular cross section, analytical formula can be applied. For arbitrary cross sections, flow resistance can be calculated by finite element analysis, for example by ANSYS or COMSOL. 
     At step  1502 , the outflow parameters are applied to an electrical circuit model of aqueous flow. To this end, the flow model of  FIG.  18    may be simplified, based on the preoperative measurements and data from studies on relative contribution of flow resistance from different tissues in the eye. For example, studies indicate that the resistance through the trabecular meshwork  12  is concentrated at the inner wall  18   a  of the Schlemm&#39;s canal  18  and the juxtacanalicular tissue  17 . See, for example, Hann C R, Vercnocke A J, Bentley M D, Jorgensen S M, Fautsch M P. Anatomic changes in Schlemm&#39;s canal and collector channels in normal and primary open-angle glaucoma eyes using low and high perfusion pressures. Invest Ophthalmol Vis Sci. 2014; 55:5834 5841. DOI:10.1167/iovs.14-14128; Rosenquist R, Epstein D, Melamed S, Johnson M, Grant W M. Outflow resistance of enucleated human eyes at two different perfusion pressures and different extents of trabeculotomy. Curr Eye Res. 1989; 8:1233-1240. Further, these studies attribute up to 50% of outflow resistance to the Schlemm&#39;s canal  18 , collector channels  19 , and the episcleral venous system at low perfusion pressures, and lesser but significant outflow resistance effects due to these components at higher perfusion pressures. Based on these studies, the flow model of  FIG.  18    may be simplified by assuming the uveal  15  and the corneoscleral meshwork  16  do not contribute to the outflow resistance and thus, eliminating the Ru resistors and the Rcs resistors from the diagram. This simplified model is shown in  FIG.  20 A . 
     Continuing with step  1502  and the simplified model of  FIG.  20 A , the modeling process continues by solving for components of the circuit diagram. Rci and Rji are determined from the relationship C=1/R, where R is the combined resistance of all indexed resistors Rc, Rs, Rj, and C corresponds to the collective hydraulic conductivity obtained in step  1500 . Further, assuming circular symmetry, then the indexed resistances of the particular tissue are all the same, where circular symmetry corresponds to a condition where the Schlemm&#39;s canal  18  has the same cross section along the circumferential angle, the trabecular meshwork  12  has the same thickness and porosity along the circumferential angle and the collector channels  19  are distributed evenly along the circumferential angle. In this case, the resistors Rsi of the Schlemm&#39;s canal are on an equipotential surface. And on and equipotential surface there is no current flowing parallel to the surface. It is further assumed that in case of a disease affecting the flow resistance, say clogging the pores of the trabecular meshwork, the disease affects the tissue the same way along the circumferential angle. Based on the foregoing, in the diagram of  FIG.  20 A , Rj1=Rj2= . . . =Rjn, Rc1=Rc2= . . . =Rcn and Rs1=Rs2= . . . Rsn. 
     A further simplified model is illustrated in  FIG.  20 B , wherein all Rs values can be eliminated, since there is no flow in the Schlemm&#39;s canal  18  in the symmetrical case. In this context, “no flow” refers to the condition where there is no circumferential flow of aqueous within the Schlemm&#39;s canal  18 . No flow does not preclude the natural flow of aqueous from the trabecular meshwork  12  through the canal  18  and directly into the collector channels  19 . Continuing with  FIG.  20 B , this simplified model can now be solved to determine values of Rc and Rj. With equal weighting of the trabecular and collector channel resistance, Rci=Rji=n/2C, where n is an arbitrary number, for example 360 for 1 degree resolution along the circumferential angle, and C is the collective hydraulic conductivity obtained in step  1500 . This solution of the equation can only be obtained with the assumption of the circular symmetry and elimination of Rs. 
     At step  1504 , the simplified model of  FIG.  20 A  is modified based on a test treatment pattern and known circuit component values. For example, with reference to  FIG.  20 C , a test treatment pattern similar to the treatment pattern P 2  shown in  FIGS.  14 B and  14 C  may be modeled by setting the values of the Rj resistors to zero in the area  921  and the remainder of the Rj resistors to the value obtained in step  1502 . The Rc resistors are also set to the value obtained in step  1502 , while the Rs resistors are set to the value obtained in step  1500 . After setting the values of the Rj resistors to zero in the area  921 , the assumption of circular symmetry no longer holds true, due to the zero values of the Rj resistors in the area  921 . 
     At step  1506 , a measure of IOP is obtained based on the model. This measure is referred to herein as a model IOP. Having thus modeled a test treatment pattern as shown in the circuit diagram model of  FIG.  20 C , the process returns to the circuit diagram model of  FIG.  20 A  where the outflow drain pressure (Pi−Pe) from Goldmann&#39;s equation that would result from the test treatment pattern of  FIG.  20 C  is calculated. This outflow drain pressure is referred to herein as surgically modified pressure or postoperative pressure and is noted as (Pi−Pe)postop. The process returns to the model of  FIG.  20 A  because with a surgical opening at a particular location, such as shown in the model of  FIG.  20 C , circular symmetry may no longer be assumed. Thus the simplification Rj1=Rj2= . . . =Rjn, Rc1=Rc2= . . . =Rcn and Rs1=Rs2=Rsn no longer applies and it is thus necessary to solve the model for an asymmetrical case. 
     To this end, the respective values for Rji, Rsi and Rci resistors obtained in steps  1500  and  1502  are used at the respective resistors locations where the tissue is left intact, and the value Rji=0 is used in the area  921  where tissue would be modified to create a channel opening. The postoperative pressure (Pi−Pe)postop may be determined by inserting the new combined resistance Rpostop=1/Cpostop and the preoperative flow F−U back into the Goldmann&#39;s equation and solving the equation (Pi−Pe)postop=(F−U)*Rpostop. In this process it is assumed that the flow rate F−U is not modified by the surgery. Similarly, the extraocular pressure Pe, does not depend on the surgical effects made on the trabecular meshwork  12  and the Schlemm&#39;s canal  18  because the preoperative extraocular pressure (Pe)preop is equal to the postoperative extraocular pressure (Pe)postop. Therefore, the change of the intraocular pressure ΔPi=(Pi−Pe)postop−(Pi−Pe)preop. The actual value of the extraocular pressure Pe is not needed for the determination of the change of the intraocular pressure ΔPi. The change of the intraocular pressure ΔPi may be used as the modeled IOP. Alternatively, based on the relationship ΔPi=(Pi)preop−(Pi)postop, and having known values for ΔPi and (Pi)preop, a value for (Pi)postop may be obtained. 
     At step  1508 , the model IOP is evaluated relative to the target IOP. For example, the value of ΔPi may be compared to a target IOP corresponding to an desired reduction in IOP, such as a 5 mm Hg reduction. Or a value for (Pi)postop may be compared to a target IOP corresponding to a desired value of IOP, such as a 15 mm Hg. At step  1510 , if the evaluation outcome is positive, meaning the model IOP satisfied the target IOP, the modeling process ends at step  1512 . If, however, the evaluation outcome is negative at step  1510 , meaning model IOP did not satisfy the target IOP, the modeling process returns to step  1504 , where the test treatment pattern is modified and the remainder of the process is repeated. The test treatment pattern may be modified iteratively until the target IOP is achieved. 
     The method described to determine an initial treatment pattern is specific to individual patients, based on their preoperative diagnosis. To perform the surgical treatment, the initial treatment pattern is programmed into the control system  100  of the surgical system  1000  and laser treatment is delivered in accordance with the treatment pattern excise or affect a surgical volume, as described in previous paragraphs and according to the block diagram on  FIG.  12   . 
     Alternatively, the initial treatment pattern can be determined by considering empirical results from previous surgeries with femtosecond laser or ELT surgery. Collection of sufficient amounts of data allows the construction of a nomogram, where treatment patterns and associated sets of surgical parameters can be quickly determined or looked up by graphical association to charted or tabulated data. Computer algorithms can also utilize data from previous surgeries to construct a surgical plan. 
       FIG.  22    is a flow chart of a method of achieving precise IOP reduction in successive multiple steps of IOP measurements and surgery. The method may be performed by one or more components of the integrated surgical system  1000  of  FIGS.  7 - 10 B . For example, the control system  100  may include a processor and a memory coupled to the processor that stores instructions that enable the processor to execute or implement the method of  FIG.  22   . 
     At step  1600 , an IOP criterion is determined for the patient. An IOP criterion may be a target IOP that is considered an acceptable outcome for the patient. Another IOP criterion may be a threshold reduction in a current IOP relative to an elevated, preoperative IOP of the patient, that considered an acceptable outcome for the patient. The IOP criterion may be based on actual measures of IOP obtained from the patient. For example, an IOP in the range of 12 to 22 mm Hg is considered normal. Accordingly, a target IOP may correspond to 12 to 22 mm Hg. A threshold reduction in IOP may correspond to, for example, at least a 20% reduction from an elevated, preoperative IOP of the patient. Yet another IOP criterion may be a minimum IOP needed to avoid harming the eye. For example, the IOP should not drop below 10 mm Hg, where the eye is considered hypotonous. Postoperative hypotony can lead to engorged retinal vessels, swollen optic discs, and folds in the choroid and retina. 
     In another configuration, the IOP criterion may be based on anatomical dimensional measures that function as surrogates for actual IOP measures. As described above with reference to  FIGS.  16 A and  16 B , a cross-section dimension, e.g., diameter, radius, circumference, or cross sectional area of the Schlemm&#39;s canal  18  may serve as a measure of IOP. For example, the Schlemm&#39;s canal  18  having a cross sectional area 4064+/−1308 μm 2 , as measured by comprehensive spectral domain OCT is considered normal. (Kagemann L, et al. Br J Ophthalmol 2014, 98(Suppl II):ii10-ii14) Accordingly, a target IOP may correspond to a cross sectional area in the range of 2756 to 5372 μm 2 . A threshold reduction in IOP may correspond to, for example, at least a 30% increase in the cross sectional area of the Schlemm&#39;s canal  18  from a preoperative cross sectional area of the patient. Yet another IOP criterion may be a maximum diameter that must not be exceeded in order to avoid harming the eye. 
     At step  1602 , an OCT beam  301  is delivered through the cornea  3  and the anterior chamber  7  into the irido-corneal angle  13 . In one embodiment, the OCT beam  301  has a resolution less than or equal to approximately 5 micrometers and is delivered to the irido-corneal angle  13  by directing the OCT beam to a first optical subsystem  1001  that includes a window  801  coupled to the cornea  3  and an exit lens  710  coupled to the window. 
     At step  1604 , an OCT image of a portion of the irido-corneal angle  13  is acquired based on the OCT beam  301  delivered to the irido-corneal angle through the first optical subsystem  1001 . To this end, an OCT return beam  301  is received through the first optical subsystem  1001  and processed at an OCT imaging apparatus  300  using known OCT imaging techniques. 
     At step  1606 , an initial treatment pattern P 1 , P 2 , P 3  is determined or designed together with a corresponding location within the eye for laser application of the initial treatment pattern. The initial treatment pattern may be designed in accordance with the method of  FIG.  21   . The treatment pattern may be defined by a set of parameters including a treatment area A and a treatment thickness t. The treatment area A may be defined by a height h and a width w, where the width may be defined in terms of a measure around the circumferential angle. The location l indicates that location around the circumferential angle where laser application of the treatment patter is to occur. The pattern may be designed, for example using the aqueous flow model described above, to satisfy an IOP criterion. For example, an IOP criterion may represent a goal of reducing the patient&#39;s preoperative IOP by a certain percentage. As previously described, the treatment pattern P 1 , P 2 , P 3  defines a three-dimensional model of ocular tissue to be modified by a laser. Thus, a laser that modifies tissue in accordance with a treatment pattern P 1 , P 2 , P 3  affects or produces a surgical volume  900 ,  901 ,  903  that resembles the three-dimensional model of the treatment pattern. 
     At step  1608 , each of an OCT beam  301  and a laser beam  201  is delivered through the cornea  3 , and the anterior chamber  7  into the irido-corneal angle  13 . In one embodiment, the OCT beam  301  and laser beam  201  have substantially equal resolutions, e.g., less than or equal to approximately 5 micrometers, and each beam is delivered to the irido-corneal angle by directing each beam to a first optical subsystem  1001  that includes a window  801  coupled to the cornea  3  and an exit lens  710  coupled to the window. The OCT beam  301  and the laser beam  201  may be collinearly directed to the first optical subsystem  1001  along a same optical path, for example by multiplexing the beams. Alternatively, the OCT beam  301  and the laser beam  201  may be non-collinearly directed to the first optical subsystem at the same time along spatially separated or angled optical paths. 
     At step  1610 , in one embodiment, a laser beam  201  is applied in accordance with the initial treatment pattern P 1 , P 2 , P 3  to modify a volume  900 ,  901 ,  903  of ocular tissue within the trabecular outflow pathway  40  to create a channel opening that reduces a pathway resistance present in one or more of the trabecular meshwork  12 , the Schlemm&#39;s canal  18 , and the one or more collector channels  19 . To this end, a laser beam  201  having a wavelength between 330 nanometers and 2000 nanometers may be scanned in multiple directions in accordance with the initial treatment pattern to thereby affect or produce a surgical volume  900 ,  901 ,  903  that resembles three-dimensional model of the initial treatment pattern P 1 , P 2 , P 3 . 
     The laser beam  201  may be applied in a continuous manner or as a multitude of laser pulses with a pulse duration between 10 femtoseconds and 1 nanosecond. The laser beam  201  causes photo-disruptive interaction with the ocular tissue to reduce the pathway resistance or create a new outflow pathway  40 . Depending on the initial treatment pattern, photo-disruptive interaction with the ocular tissue may create, for example: 1) a deep channel opening  920  opened through the trabecular meshwork connecting the anterior chamber and the Schlemm&#39;s canal, such as shown  FIG.  11 B , 2) a shallow channel opening  921  that extends through the juxtacanalicular tissue  17  and partial into the corneoscleral meshwork  16 , such as shown in  FIG.  14 B , or 3) an array of shallow sub-openings  923  that extend through the juxtacanalicular tissue  17  and partial into the corneoscleral meshwork  16  such as shown in  FIG.  15 B . Numerous types of channel openings may be created based on different designs of treatment patterns. 
     In another embodiment, at step  1610  a laser beam  201  is applied in accordance with the initial treatment pattern to produce a pneumatic expansion of the Schlemm&#39;s canal  18 , and the one or more collector channels  19  by applying the laser beam  201  to the interior of the canal. The initial treatment pattern places the focus of the laser beam  201  inside of the Schlemm&#39;s canal  18  to avoid modification of ocular tissue. The laser beam  201  has a wavelength between 330 nanometers and 2000 nanometers and is scanned in accordance with the surgical parameters of the initial treatment pattern to thereby form microscopic gas bubbles that affect a pneumatic expansion of the Schlemm&#39;s canal  18  as described above with reference to  FIG.  16 B . 
     At step  1612 , after a short period of time to allow the aqueous flow to stabilize in the eye, a current, postoperative IOP measure, e.g., an actual IOP measure or an anatomical measure, is obtained and evaluated against the IOP criterion determined at step  1600 . At step  1614 , if the evaluation outcome at step  1612  is acceptable, the process proceeds to step  1616 , where the surgical procedure is ended. An evaluation outcome may be acceptable, for example, when the postoperative IOP is at or below a target IOP, or when the postoperative IOP represents an acceptable reduction relative to the patient&#39;s preoperative IOP. 
     Returning to step  1614 , if the evaluation outcome is not acceptable, the process proceeds to step  1618  to determine a subsequent treatment pattern and corresponding location in the eye for laser application of the treatment pattern. Steps  1608  and  1610  are then repeated using the subsequent treatment pattern, followed by evaluation steps  1612  and  1614 . These successive steps of treatment pattern modification, laser treatment and evaluation can be repeated again until the evaluation outcome of steps  1612  and  1614  is acceptable. 
     Regarding step  1618 , the subsequent treatment pattern may be determined using the aqueous flow model method of  FIG.  21    used to determine the initial treatment pattern. Alternatively, the subsequent treatment pattern may be based on the initial treatment pattern with changes in one or more of the surgical parameters of the initial treatment pattern. For example, the subsequent treatment pattern may have the same treatment area A as the initial treatment pattern, but an increased thickness d. Or the thickness t of the new treatment pattern may be the same as the initial treatment pattern with an increase in treatment area A. The subsequent location l for the subsequent treatment pattern may locate the pattern anywhere around the circumferential angle of the eye. For example, the location l may place the subsequent treatment pattern 180 degrees around the circumferential angle from the initial treatment pattern, or a number of degrees that locates the pattern closer to the initial treatment pattern. In some cases the subsequent treatment pattern may be located immediately adjacent to the initial treatment pattern or located so that it partially overlaps with the initial treatment pattern. In some instances, the subsequent treatment pattern may be the same as the initial treatment pattern, with the only change being a change in location l around the circumferential angle. 
     A change in the IOP can be observed within several minutes after surgery and it may take several days for the IOP to stabilize. Therefore, it is advantageous to wait between successive steps of surgery. Stabilization of the IOP involves several processes and there are several timescales involved. Mechanical disturbance to the eye occurs when attaching the surgical system  1000  to the eye, or by weighted tonometry. It takes several minutes, up to ten minutes, for the eye to stabilize after these mechanical disturbances. Gas bubbles created by the laser may prevent postoperative assessment until the gas is dispersed and dissolved within the ocular tissue. Gas dissolves in the tissue in less than approximately 30 minutes. Stabilization of the eye after the short term disturbances allow retreatment during the same day, not requiring re-scheduling the patient for a second visit to the treatment facility. Cellular responses to trauma, immune response and inflammation may take a day to start and several days to clear. Therefore, it does not significantly affect IOP measurement taken the same day after the surgery. Long term healing effects can last for several months after surgery. These time scales are considered for the waiting period between successive surgeries, re-evaluations and re-treatments. Multiple measurements at different times facilitate achieving higher accuracy and prediction of anticipated IOP values at future times. 
     The various aspects of this disclosure are provided to enable one of ordinary skill in the art to practice the present invention. Various modifications to exemplary embodiments presented throughout this disclosure will be readily apparent to those skilled in the art. Thus, the claims are not intended to be limited to the various aspects of this disclosure, but are to be accorded the full scope consistent with the language of the claims. All structural and functional equivalents to the various components of the exemplary embodiments described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. § 112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.” 
     It is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.