Patent Publication Number: US-8540659-B2

Title: Delivery system and method of use for the eye

Description:
RELATED APPLICATIONS 
     This is a divisional of U.S. patent application Ser. No. 09/860,842, filed May 21, 2001, which claims the benefit of U.S. Provisional Application No. 60/205,846, filed May 19, 2000, both of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTIONS 
     This invention relates to devices and methods for treatment of human tissues, especially interior human tissue structures in the eye for restructuring, and more particularly to treatment of glaucoma. 
     BACKGROUND 
     Glaucoma, a serious long-term health care problem, is a disorder of the eye in which elevated intraocular pressure ultimately leads to damage to the optic nerve and to blindness. Glaucoma has been cited as the second most common cause of blindness affecting several million people in the United States alone. 
     In order to fully appreciate the present invention, a brief overview of the anatomy of the eye is provided. As schematically shown in  FIG. 1 , the outer layer of the eye includes a sclera  17  that serves as a supporting framework for the eye. The front of the sclera includes a cornea  15 , a transparent tissue that enables light to enter the eye. An anterior chamber  7  is located between the cornea  15  and a crystalline lens  4 . The anterior chamber  7  contains a constantly flowing clear fluid called aqueous humor  1 . The crystalline lens  4  is connected to the eye by fiber zonules, which are connected to the ciliary body  3 . In the anterior chamber  7 , an iris  19  encircles the outer perimeter of the lens  4  and includes a pupil  5  at its center. The pupil  5  controls the amount of light passing through the lens  4 . A posterior chamber  2  is located between the crystalline lens  4  and the retina  8   
     As shown in  FIG. 2 , the anatomy of the eye further includes a trabecular meshwork  9 , which is a narrow band of spongy tissue that encircles the iris  19  within the eye. The trabecular meshwork has a variable shape and is microscopic in size. It is of a triangular cross-section and of varying thickness in the range of 100-200 microns. It is made up of different fibrous layers having micron-sized pores forming fluid pathways for the egress of aqueous humor. The trabecular meshwork  9  has been measured to about a thickness of about 100 microns at its anterior edge, Schwalbe&#39;s line  18 , which is at the approximate juncture of the cornea  15  and sclera  17 . 
     The trabecular meshwork widens to about 200 microns at its base where it and iris  19  attach to the scleral spur. The passageways through the pores in trabecular meshwork  9  lead through very thin, porous tissue called the juxtacanalicular trabecular meshwork  13  that in turn abuts the interior side of a structure called Schlemm&#39;s canal  11 . Schlemm&#39;s canal  11  is filled with a mixture of aqueous humor and blood components and branches off into collector channels  12  which drain the aqueous humor into the venous system. Because aqueous humor is constantly produced by the eye, any obstruction in the trabecular meshwork, the juxtacanalicular trabecular meshwork or in Schlemm&#39;s canal prevents the aqueous humor from readily escaping from the anterior eye chamber which results in an elevation of intraocular pressure within the eye. 
     As shown in  FIG. 2 , the eye has a drainage system for the draining aqueous humor  1  located in the corneoscleral angle  200 . In general, the ciliary body  3  produces the aqueous humor  1 . This aqueous humor flows from the posterior chamber  2  through the pupil  5  into the anterior chamber  7  to the trabecular meshwork  9  and into Schlemm&#39;s canal  11  to collector channels  12  to aqueous veins. The obstruction of the aqueous humor outflow which occurs in most open angle glaucoma (i.e., glaucoma characterized by gonioscopically readily visible trabecular meshwork) typically is localized to the region of the juxtacanalicular trabecular meshwork  13 , which is located between the trabecular meshwork  9  and Schlemm&#39;s canal  11 , more specifically, the region of the inner wall of Schlemm&#39;s canal. It is desirable to correct this outflow obstruction by enhancing the eye&#39;s ability to use the inherent drainage system. 
     When an obstruction develops, for example, at the juxtacanalicular trabecular meshwork  13 , intraocular pressure gradually increases over time. Therefore, a goal of current glaucoma treatment methods is to prevent optic nerve damage by lowering or delaying the progressive elevation of intraocular pressure. Many have searched for an effective method of lowering and controlling intraocular pressure. In general, various pharmaceutical treatments have been employed to control intraocular pressure. While these treatments may be effective for a period of time, the intraocular pressure in the diseased eyes often increases in many patients. The most frequent problems result from patients failing to follow their treatment regimen thus causing inadequately controlled glaucoma, which results in irreversible damage to the optic nerve that ultimately results in vision loss. 
     After a trial of pharmaceutical treatments fails to stop the progression of elevated intraocular pressure, or in some cases as primary therapy, a surgical treatment method or procedure is generally performed on the eyes of the patients. The human eye is a particularly challenging target for corrective surgery because of the size, fragility, distribution and characteristics of interior tissues. Surgical attempts to lower the intraocular pressure include various therapies that generally fall under the name “glaucoma filtering surgery”. 
     The surgical therapies in current use, however, do not address the location of the outflow obstruction that is recognized for causing the elevated intraocular pressure. These procedures include mechanically cutting portions of the eye anatomy and are known by such names as trabeculectomy, trabeculotomy, goniotomy and goniocurettage. Significantly, these techniques have been found to be unsuccessful for long term intraocular pressure control. Trabeculectomy has been the most popular procedure in glaucoma surgery in which an opening is created in the sclera to enable aqueous humor to drain into channels external to the eye globe. This procedure, however, has many complications including leaks, infections, hypotony (e.g., low eye pressure), and requirements for post-operative needling, undesirable antimetabolite use, a need for flap suture adjustment to maintain the function of the opening and a need for long-term monitoring to avoid late complications. Another procedure, called deep sclerectomy, attempts to create an intrascleral filtration pocket, but does not alter anatomic relationships and does not treat the region of outflow obstruction. Another procedure, called viscocanalostomy, does attempt to alter the outflow obstruction between Schlemm&#39;s canal and the porous juxtacanalicular layer. In viscocanalostomy, an opening via the sclera is created in an attempt to localize and insert a tube into Schlemm&#39;s canal without puncturing the trabecular meshwork. Schlemm&#39;s canal is dilated by injection of viscoelastic materials into the canal. By altering the juxtacanalicular meshwork&#39;s anatomic relationships, an increased aqueous outflow results. Although attempting to address the outflow obstruction that causes the increased intraocular pressure, viscoanalostomy has not been shown to be successful. Thus, a new effective treatment method was needed for glaucoma to address the outflow obstruction that causes elevated intraocular pressure. 
     In the prior art, lasers have been used to treat glaucoma. Specifically, lasers have been used to thermally modify and/or to puncture completely through various structures, including the trabecular meshwork, Schlemm&#39;s canal and the sclera. Moreover, lasers have been used in attempts to open the anterior chamber to an internal outflow rather than an external outflow channel, or reservoir. Early attempts utilized the lasers available at that time which included Q-switched ruby lasers, neodymium:yttrium aluminum garnet (Nd:YAG) lasers, and argon lasers. These procedures had many names: laser trabeculopunture, laseropuncture, goniopuncture, laser trabeculostomy, laser trabeculotomy, and laser trabeculoplexy. The above described procedures attempted to remove or move or alter portions of the trabecular meshwork. The procedures have several shortcomings. First, they have limited ability to lower the intraocular pressure to a desirable level. Second, while most found initial success in creating a puncture through the meshwork, the short duration of the reduced intraocular pressure proved to be ineffective in treating the long term effects of glaucoma. As a result, patients suffered undesirable additional post operative procedures to lower the intraocular pressure and required continuous long-term monitoring. The short duration of the reduced pressure has been linked to the body&#39;s subsequent inflammatory healing response at the openings created in the eye. The trauma associated with the shearing and tearing of the tissues and the thermal tissue damage caused by the above procedures initiates wound-healing processes which tend, with time, to reseal the created openings. 
     These early laser procedures failed in that no consideration was given to the size of the openings in the trabecular meshwork. In addition, these procedures also failed to recognize the importance of reducing collateral tissue damage surrounding the created hole. It has been seen that large areas of surrounding tissue damage invite greater inflammation that results in a greater healing response. In addition, if damage occurs to the outer wall of Schlemm&#39;s canal and collector channel openings, resultant scarring prevents aqueous humor egress through the distal outflow pathways and effectively eliminates any benefit of the attempted procedure. The actual and potential thermal effect produced by the lasers is a significant contributing factor to the resultant tissue damage. Therefore, the opening size and tissue damage needs to be controlled by controlling the thermal trauma to the target tissues. 
     SUMMARY 
     The present invention is an improved glaucoma treatment by providing a method and delivery system for creating an aqueous outflow pathway through the trabecular meshwork, juxtacanalicular trabecular meshwork and Schlemm&#39;s canal of an eye in order to reduce elevated intraocular pressure. The method includes the steps of introducing a fiber-optic probe between the outer surface of the eye and the anterior chamber until a distal end of the fiber-optic probe is in contact with or adjacent to a target site including the trabecular meshwork, the juxtacanalicular trabecular meshwork and Schlemm&#39;s canal distal to the meshwork. Pulsed laser radiation is delivered from the distal end of the fiber-optic probe sufficient to cause photoablation of the juxtacanalicular trabecular meshwork and an inner wall of Schlemm&#39;s canal in the target tissues. The fiber-optic probe may be stationery or advanced creating an aperture through these tissues to enable and improve fluid flow from the anterior chamber of the eye. The pulsed radiation is delivered in wavelengths, pulse durations and fluences to cause a minimal thermal effect on the tissue while removing and modifying tissue. 
     In a second aspect of the invention, a method of controlling an interior anatomy of an eye during an intraocular procedure includes the steps of creating an opening in the eye, and filling the anterior chamber of the eye through the opening with a viscoelastic material. The interior pressure within the eye may be sensed with a pressure sensor. The interior pressure may be adjusted by controlling the amount of viscoelastic material so as to compress or decompress the interior anatomy of the eye at a predetermined target anatomy site. In one aspect, the interior anatomy includes the trabecular meshwork. Viscoelastic materials of various viscosities and other protective agents placed within structures enable micro-manipulation of such structures for surgical modification while protecting adjacent structures from possible damage. Schlemm&#39;s canal may be inflated to enable perforation of the inner wall while protecting the outer wall structures. 
     In a third aspect of the invention, a method of reducing intraocular pressure in an eye is provided by creating an aqueous flow pathway through the trabecular meshwork and the inner wall of Schlemm&#39;s canal in which an implant device is inserted into the aqueous flow pathway and serves as a conduit to remove aqueous humor. The implant device may extend from the anterior chamber of the eye or the trabecular meshwork to the inner wall or lumen of Schlemm&#39;s canal. 
     In a fourth aspect of the invention, an apparatus provides laser energy to target tissues of an eye. The apparatus includes a laser unit for generating laser energy, and a delivery system that includes a laser probe. The laser probe includes an optical fiber core for transmitting laser energy from a distal end to target tissues of the eye, and a proximal end for coupling to the laser unit and may include sensing devices which generate and receive signals to enable a controller. In one embodiment, the sensing device features a sensor for sensing the temperature in the eye and at the target tissues before, during and after photoablation of the target tissues. In another embodiment, the sensing device has a sensor for sensing the laser probe relationship to the target tissues. In a further embodiment, the sensing device has a sensor for sensing the pressure both within the eye and at the probe/target tissues. A servo feedback mechanism may utilize sensed pressure to provide a controlled adjustment of the treatment parameters. 
     In a fifth aspect of the invention, a device for reducing and maintaining reduced intraocular pressure is implanted into at least an inner wall of Schlemm&#39;s canal or adjacent trabecular meshwork. The device may include a tubular portion having a distal end including a first engaging member for attaching to the interior surface of the proximal inner wall of Schlemm&#39;s canal or adjacent trabecular meshwork. The tubular portion includes a proximal end having a plurality of second engaging members for attaching to the trabecular meshwork. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing summary of the invention, as well as the following detailed description of the preferred embodiments is better understood when read in conjunction with the accompanying drawings, which are included by way of example, and not by way of limitation with regard to the claimed invention, wherein: 
         FIG. 1  is schematic sectional view of an eye illustrating the interior anatomical structure; 
         FIG. 2  is a perspective fragmentary view of the anatomy within the anterior chamber of an eye depicting the comeoscleral angle; 
         FIG. 3  is schematic sectional view of an eye illustrating a fiber-optic probe disposed next to the trabecular meshwork in the anterior chamber of the eye; 
         FIG. 4  is a schematic diagram of an embodiment of a laser delivery system including a side-sectional fragmentary view of the operative end of a fiber-optic probe 
         FIGS. 5A-5F  are schematic diagrams of alternative embodiments of a tip of a fiber-optic probe; 
         FIG. 6  is a schematic diagram of an embodiment of control switches as may be on a handset for a fiber-optic probe; 
         FIG. 7  a schematic diagram of an embodiment of temperature sensing circuitry of a laser delivery system; 
         FIGS. 8A and 8B  are schematic diagrams of various tissue sensing circuitry for use in a laser delivery system; 
         FIG. 9  is a schematic diagram of pressure sensing circuitry of a laser delivery system; 
         FIG. 10  is a flow chart of an embodiment of operating a servo device of a laser delivery system; 
         FIGS. 11A-B  are schematic diagrams of alternative embodiments of tissue guidance circuitry of a laser delivery system; 
         FIG. 12  is a schematic diagram of an embodiment of a motion controller for a fiber-optic probe; 
         FIG. 13  is a block diagram of an embodiment of a method of treating glaucoma with a laser delivery system; 
         FIG. 14  is a schematic diagram of a fiberoptic probe for providing fluids/materials into Schlemm&#39;s canal. 
         FIG. 15  is a schematic diagram of a first embodiment of an intraocular intracannalicular implant device; 
         FIG. 16  is a schematic diagram of a second embodiment of an intraocular intracannalicular implant device; 
         FIG. 17  is a fragmentary schematic diagram of a system for implanting the devices of  FIGS. 15 and 16  into the eye; 
         FIGS. 18A-18B  are schematic diagrams of a system for providing fluids/materials in Schlemm&#39;s canal; 
         FIG. 19  is a schematic diagram of an irrigation system for use a laser delivery system; 
         FIGS. 20A-20B  are schematic diagrams of a beveled face fiber-optic tip photoablating target tissues; and 
         FIGS. 21A-21B  are schematic diagrams of alternative heat extraction systems for a probe in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 3-12  illustrate an embodiment of a laser delivery system  21  for micromachining, microscupting, or microshaping the interior anatomy of an eye. As shown in  FIG. 4 , a laser delivery system  21  may be operated to reduce the thermal component of laser energy contributing to collateral tissue damage. As further shown in  FIG. 4 , laser delivery system  21  includes a fiber-optic probe  23  for entering the eye and removal or manipulation of eye tissue. Fiber-optic probe  23  is mechanically and electrically coupled to a probe handset  25 . Probe handset  25  includes controls for manipulating and operating the fiber-optic probe. A servo device  27  is connected to fiber-optic probe  23  for automatically controlling pressure within the eye during an intraocular procedure. If desired, a motion controller  29  may selectively automate transocular movement of fiber-optic probe  23  into a desired site for tissue removal and/or manipulation. A laser unit  31  provides laser energy in the form of wavelength pulses through fiber optic probe  23  for tissue removal from the interior of the eye by photoablation. Photoablation is the process of removing surface tissues, typically via laser energy, with minimal thermal transfer to the remaining tissues. 
     Referring to  FIGS. 3 and 13 , an overview of a manner of operating laser delivery system  21  for treatment of glaucoma or other eye conditions follows.  FIG. 3  is a side sectional view of the interior anatomy of a human eye showing fiber-optic probe  23  in relation to treating glaucoma. After applying local and/or retrobular anesthesia to eliminate pain, a small self-sealing incision  14  is created in the cornea  15  with a surgical blade or other device. The anterior chamber is stabilized with a viscoelastic agent. Fiber-optic probe  23  is positioned and advanced in the incision  14  into the anterior chamber  7  until a distal end of fiber-optic probe  23  contacts or is adjacent to the desired target tissues for removal. Laser energy produced by laser unit  31  is delivered from the distal end of fiber-optic probe  23  in contact or adjacent to the tissues sufficient to cause photoablation of tissues which may include the trabecular meshwork  9 , the juxtacanalicular trabecular meshwork  13  and an inner wall of Schlemm&#39;s canal  11  as the target tissues. Fiber optic probe  23  may be advanced towards Schlemm&#39;s canal  11  and creates an aperture in the proximal inner wall of Schlemm&#39;s canal  11 , but does not perforate the distal outer wall. If desired, additional apertures may be created in the trabecular meshwork and target tissues. Thus, the resultant aperture or apertures restore the natural drainage system for the aqueous humor. 
     Referring to  FIG. 4 , fiber-optic probe  23  is illustrated having similar structure as structure disclosed in U.S. Pat. No. 4,846,172 to the present inventor, which is herein fully incorporated by reference. Probe  23  includes an axially disposed light transmitting core  33  having an optical fiber or a plurality of optical fibers  35  in which core  33  is stiffened by an encapsulating sheath  37 . The diameter of a single optical fiber  35  should be sufficiently large to transmit sufficient light energy for causing photoablation of target tissues and are typically in a range from 4-6 microns. A single optical fiber or a plurality of optical fibers  35  may be used in a bundle of a diameter ranging from 100 to 1000 microns. Core  33  and sheath  37  are encased within an outer metal sleeve or shield  39  that is typically constructed of stainless steel. The outer diameter of sleeve  39  is preferably no larger than 1000 microns. If desired, the diameter may be as small as 100 microns, when smaller optical fibers are implemented with laser delivery system  21 . If desired, the sleeve may be flexible so that it can be bent or angled. 
     The tip or distal end  41  of probe  23  may be inclined with respect to a central longitudinal axis  43  extending between distal end  41  and a proximal end  45  of the probe. The angle of the inclination is preferably about 45 degrees and may range from 0 to 180 degrees. The inclined geometry orients the distal end  41  of probe  23  relative to the surface of the target tissues so that photoablative decomposition of target tissues proceeds uniformly and so that distal end  41  of probe  23  is oriented to enable photoablation of the target tissues. 
     The tip  47  of the optical fiber or fibers  35  emanates light with controlled divergence so that a laser spot size encompasses a larger target area than the fiber cross sectional diameter. This enables perforations in target tissues to have a larger diameter than the probe sleeve  39  and also reduces thermal tissue damage. Generally, tip  47  of the optical fiber or fibers  35  is shaped such that each tip has a unique energy distribution and therefore is best suited to a particular need. In alternative embodiments, as shown in  FIGS. 5A-5F , fiber tip  47  may be shaped in a plane normal to the longitudinal axis  43  (see  FIG. 5A ) or, a concave shape (see  FIG. 5B ) or a convex shape (see  FIG. 5C ) to obtain virtually any desirable spot size on the target tissues. In addition to controlling laser spot size, it may be desirable to control the direction of the laser energy being delivered from distal tip  47 . As shown in  FIG. 5D , distal fiber tip  47  may have a beveled face to form a cone shaped pattern of light pointing downward from the face. As shown in  FIG. 5E , a beveled faced distal fiber tip  47  may further include a microprism  40  that provides directional control of the light pattern. As shown in  FIGS. 20A-B , a cone-shaped laser energy distribution is delivered from the beveled faced fiber tip  47  such that fiber tip  47  may be oriented for precise photoablation of the target tissues. If desired, the inclined shape of distal end of probe  23  may be aligned with beveled face fiber tip  47 . Fiber tip  47  may extend beyond distal end  41  to enable more precise control over the procedure. 
     Other mechanisms may be used to control the laser spot size. As shown in  FIG. 5F , a transparent spacer or window  44  may be abutted by a micro lens  42  (or a microprism) and is attached to distal fiber tip  47  to achieve a desired spot size of the laser energy on the target tissues. Micro lens  42  is designed such that the target area or spot size, energy distribution and direction of the laser energy can be controlled. Spacer  44  prevents fiber tip  47  from contacting target tissues during the photoablation process. Such arrangement reduces any likelihood that waste products from the process are deposited on the fiber tip  47 . Fiber tip  47  may also be maintained free of waste material collecting on it by providing a gas or fluid flow, including a viscoelastic fluid, across the tip. It should be recognized that micro lens  42  and the spacer are generally sized so as to match the diameter of the attached optical fiber. 
     Still referring to  FIG. 4 , in order to reduce or control possible damaging thermal effects on the target tissues, an irrigation fluid, such as a saline solution, is provided to cool the target tissues. The irrigation fluid is generally aspirated from the eye to prevent overpressure and vent gases during photoablation. Fiber-optic probe  23  may include side-by-side semicircular passageways within and along the interior of sleeve  39  forming an irrigation flow path  49  and a separate aspiration flow path  51 . Distal end  41  of probe  23  includes terminal openings for flow paths  49 ,  51  at distal end  41 . These openings may also be positioned along the probe near the terminal end. The terminal openings may be coaxial or in an angled relationship to the light transmitting core  33 . Proximal end  45  of probe  23  links flow paths  49 ,  51  into corresponding flow paths in handset  25 . The coupling can be accomplished by known approaches for laser probes. Although the irrigation and aspiration flow paths  49 ,  51  have been described been in a side-by-side relationship within the sleeve  39  they may also be provided as concentric tubes about a central optical fiber or the infusion/aspiration path flow may be central and the optical fiber adjacent its periphery. Referring to  FIG. 19 , it is contemplated that fiber optic core  33  may have a hollow cylindrical pathway  53  extending along the center axis for providing irrigation or an aspiration pathway as desired. In addition, alternative approaches of the flow path construction based on fiber optics advances may be employed with optical fibers up to 100 microns. Also, other specialized fibers can enable the associated irrigation and aspiration passageways to be arranged in other ways including within the fiber core(s). 
     Continuing to refer to  FIG. 4 , flow paths  49 ,  51  in probe  23  are connected to an irrigation system  55  and an aspiration system  57  of laser delivery system  21 . Each system  55 ,  57  will be described in detailed herein. Irrigation system  55  supplies a desired irrigation fluid into probe handset  25  via a flexible tubular line under a gravity-feed configuration or a pumped configuration. In the case of a pump configuration, the irrigation fluid is pumped from a sterile reservoir or container  24  into handset  25 ; the fluid then flows under pump pressure in irrigation pathway  49  to probe  23  distal end  41  and to target tissues. 
     Rather than using an irrigation fluid for cooling the target site, a viscoelastic fluid from the irrigation system  55  can be pumped into handset  25  and into probe  23  for cooling the target site. In addition, a viscoelastic fluid may also be used to compress or flatten the trabecular meshwork in the eye, to control its dimensions. Viscoelastic materials for use with the present invention ideally should have a molecular size that is larger than the pore size of the target tissues in order to be able to tampanade or push away the tissue rather than diffusing into it. Properly selected viscoelastic fluids can be used to compress the trabecular meshwork  9  (see  FIG. 2 ) to a reduced thickness and to stabilize the meshwork for eventual removal of selected portions of tissue by laser photoablation. 
     Alternatively, a viscoelastic fluid may include combinations of therapeutic agents to prevent inflammation at the target site for keeping the apertures open. For example, viscoelastic fluid may be combined physically and/or chemically with, anti-inflammatory agents, steroidal and non-steroidal, anti-angiogenic agents, anti-fibroblast agents, and various other combinations of agents. Specific examples of these types of agents include DFU, which is a nonsteroidal anti-inflammatory, anecortave acetate which is one of the angiostatic steroids, and anti-TGF which is a monoclonal antibody known to inhibit the activity of all three forms of TGF-.beta. in vivo. An example of an available viscoelastic material having a non-steroidal anti-inflammatory agent is disclosed in U.S. Pat. No. 5,811,453 to Yanni et al., which is herein fully incorporated by reference. 
     Controls switches  61  on the handset  25 , a foot pedal, or other control device may be used by the surgeon to initiate flow of the fluid by valve and/or pump control. Irrigation fluid flow may be commenced along with the laser energy delivery to the target tissues. Alternatively, the flow of fluid with the start of laser unit  31  may be automatically regulated by other devices. Referring to  FIG. 6 , handset  25  may include a plurality of control switches  61   a - 61   e  for operating laser delivery system  21 . 
     Control switches  61   a - 61   e  perform the same or all of the following functions for operating laser delivery system  21 , such as switch  61   a  for arming and firing laser unit  31 ; switch  61   b  for controlling irrigation system  55 ; switch  61   c  for controlling aspiration system  57 ; switch  61   d  for controlling servo device  27 , and switch  61   e  for controlling motion controller  29 . The control switches optionally may be mounted on a separate unit, such as a remote control unit. 
     Aspiration system  57  enables the extraction of fluid from the eye and also enables immediate extraction of the gases generated from the photoablative decomposition process to escape through aspiration flow path  51  through flexible lines in handset  25 . Aspiration system  57  may function passively or may include a sufficiently sized vacuum pump for enabling waste fluid to be suctioned into a waste container or canister  58 . Aspiration system  57  allows gases to be removed without otherwise heating the local tissues. Thus, aspiration system  57  advantageously reduces thermal tissue damage. 
     Laser delivery system  21  may further include a laser unit  31  for providing a beam of periodic light pulses of sufficient fluence to initiate and sustain photoablation of the target tissues in contact with distal end  47  of probe  23 . In one embodiment, laser unit  31  comprises a xenon chloride excimer laser operating at a 308 nm wavelength having a fluence ranging from 1 to 60 mJ/mm.sup.2 per pulse and a repetition rate ranging from 5 to 75 Hertz. The corresponding repetition rate can be varied to compensate for the thermal time constant of the tissues in relation to the fluence of the laser energy radiating the target tissues. The 308 nm wavelength is selected to be absorbed preferentially by eye tissues rather than any intervening aqueous humor or any viscoelastic fluid between the tissues. The previously described laser parameters significantly reduce the thermal component of the laser energy and accordingly, resultant collateral tissue damage is minimized. Alternatively, laser unit  31  may be a solid state 2.94 micron Er:YAG laser. This wavelength may be delivered to the target tissue through probe  23  via light transmitting core  33 . In addition, laser unit  31  may includes a safety circuit to preclude inadvertent triggering. The various laser parameters may be adjusted accordingly to calibrate laser unit  31  for use on a variety of target tissues. A 355 nm solid state laser may also be used as laser unit  31 . One of ordinary skill in art may consider calibration factors such as the homogeneity of the output of the light beam, minimizing the pulse-to-pulse energy variation, the suprathreshold fluence value, and reducing the thermal component of laser-tissue interaction. 
     In an alternative embodiment, a laser operating at wavelengths in the ultraviolet range from 100 to 400 microns may be utilized to cause photoablation of the target tissues. In yet another embodiment, a laser operating in the infrared wavelengths ranging from 2.5 to 6.5 microns may also comprise laser unit  31 . In seeking to minimize the thermal damage to target tissues, if the temperature in the target site reaches a predetermined level established as undesired, then the periodic time between pulses may be lengthened in the range from 5 to 20 Hz. Generally, for use with the present invention, the lasers selected have a short penetration depth which allows for sufficient precision per laser pulse and controlled energy distribution. With ultraviolet lasers, the penetration depth is typically in a range from 0.5 to 1.5 microns; for infrared lasers, the penetration depth is typically in a range from 1-2 microns. 
     In one embodiment, as illustrated in  FIG. 7 , laser delivery system  21  may include temperature measurement circuitry for sensing temperature at and around the target site and for minimizing collateral thermal damage at and around the target tissues. In this embodiment, distal end  41  of probe  23  may include a thermocouple  65  that is thermally isolated from sleeve  39  by an insulating pad  67 . Thermocouple  65  and insulating pad  67  are sized for use with probe  23 . Conductors  69  from the thermocouple  65  extend through probe  23  to transmit a feedback signal to an external controller  71 . The external controller  71  may indicate or otherwise display the internal temperature sensed by thermocouple  65 . In one arrangement, controller  71  alerts the surgeon when the temperature exceeds a predetermined level. If desired, external controller  71  may be operatively coupled to laser unit  31  for automatically self adjusting the repetition rate of the laser based on the sensed temperature. This enables external controller  71  to operate to minimize the thermal effect on the target tissues. Probe sleeve (stainless steel) may be cooled externally near the handpiece cooling flow may be conducted along the sleeve to affect the probe tip and adjacent tissues. 
     Fiber optic probe  23  may also include a heat extraction system for reducing the thermal component of the laser-tissue interaction during the photoablation period. By removing heat, the heat extraction system may be used to complement the minimal thermal tissue removal of laser unit  31  in order to reduce collateral damage to target tissues from the laser energy. The heat exchanging system may cool sleeve  39  of probe  23  by a heat sink. In one arrangement, the heat sink may be a cooling working liquid that flows in the interior of probe sleeve or cools the probe sleeve by conduction from the handpiece. As shown in  FIG. 21A , in an alternative arrangement, an appropriately designed thermoelectric device  121  may be mounted in the interior of the probe  23  or the handpiece  25 , such a Peltier cooling device for example. Thermal electric device  121  may be sealed from the fluid in aspiration pathway  51 . Device  121  may be coupled to tubular sleeve  39  such that heat may be removed from the surrounding fluid in the eye contacting probe  23 . In this case, device  121  may be fluid or water cooled such that fluids flowing in aspiration pathway  51  transfers heat from device  121  to waste container  58 . Alternatively, thermal electric device  121  may be mounted on the exterior of tubular sleeve  39  near proximal end  45  in handset  25 . In such a case, device  121  may be air cooled for transferring extracted heat to the air. In both cases, signal wire  123  provides electric power to operate device  121  and extends to a thermal electric controller  125 . Controller  125  controls the operation of device  121  by turning electric power on and off. Controller  125  may be coupled to external controller  71  in order to operate thermal electric device  121  when the sensed temperature in the eye reaches a predetermined level. A thermal insulating sleeve may be provided on the exterior of tubular sleeve  39  to prevent cooling of the cornea and/or the anterior chamber by probe  23 . The thermal insulating sleeve may extend near the proximal end of probe  23 . Other cooling alternatives may include Venturi cooling or convection cooling. Referring to  FIG. 21B , with Venturi cooling, a Venturi orifice  131  may be mounted in irrigation pathway  49 . One skilled in the art would recognize various other alternatives to cooling the probe may be performed. 
     In another embodiment, referring to  FIG. 8A , laser delivery system  21  may include tissue sensing circuitry for determining when fiber-optic probe  23  is adjacent to or in contact with tissues in the target site. In one arrangement, distal end  41  of probe  23  includes a microswitch  73  for sensing physical contact with tissues, for example, the trabecular meshwork  9 . Microswitch  73  may be constructed from a biocompatible material suitable for internal use. Microswitch  73  may be formed in a number of configurations as long as a contact signal is transmitted via signal wires  74  to controller device  75 . Signal wires  74  may be installed in a small liquid-tight conduit inside of probe  23  that extend to the proximal end. The contact signal may be a completion of an electrical circuit between switch  73  and controller device  75 . Controller device  75  processes the contact signal which may be used both to alert the surgeon that probe-tissue contact has been achieved and in a feedback loop to control laser functions. The alert may be in the form of a lighted display, sound, or other indicator. In addition, the tissue-contact signal may be processed to prevent triggering of laser unit  31  until tissue contact is achieved. As a result, undesired firing of laser unit  31  is avoided, thus reducing the chance of overheating the aqueous humor or other fluid in the anterior chamber. It should be recognized that the tissue-contact signal ceases when microswitch  73  is deactivated by not being in contact with the tissue. 
     Turning to  FIG. 8B , contact with the eye tissue, such as the trabecular meshwork, alternatively may be detected by a pair of microelectrodes  77  mounted on an insulator substrate at distal end  41  of probe  23 . Microelectrodes  77  are coupled to signal lines  79  that extend along sleeve  39  to an external gap detector circuit  81 . The circuit  81  responds to a threshold change in conductivity or capacitance when the target tissues, for example, the trabecular meshwork, are contacted or within an adequately small distance from the tip. Distance is defined as a function of the dielectric using the probe as one plate and the tissue as a second plate of a capacitor. In order to detect a change in conductivity or capacitance, it is recognized that the aqueous humor and the trabecular meshwork possess different dielectric values. Referring to  FIGS. 3 and 8B , when probe  23  enters the anterior chamber  7 , the electrodes  77  are located in the aqueous humor. When microelectrodes  77  enter or contact the trabecular meshwork, for example, the dielectric value between the electrode changes. As a result, there is corresponding change in capacitance indicating that probe  23  has contacted tissue. 
     Laser delivery system  21  may include circuits for preventing the firing of laser unit  31  when the fiber tip  47  is too far separated from the target tissue in order to prevent undesirable thermal heating of aqueous humor and/or the viscoelastic fluid. This is achieved by the probe-tissue contact signal generated by microswitch  73  ( FIG. 8A ) located at distal end  41  of probe  23 . The probe-tissue contact signal is triggered by conductivity changes occurring to tissue compression and relative tissue/aqueous composition. Alternatively, probe-tissue contact signal or a proximity signal, as previously described, may be generated by microelectrodes  77  ( FIG. 8B ) located at distal end  41  of probe  23  to prevent firing of laser unit  31 . Also, the handset  25  may use the signal to activate the laser unit  31  or allow it to be fired if further closure of the gap is needed. 
     Turning to  FIG. 9 , laser delivery system  21  may include pressure sensing circuitry for detecting and controlling pressure both at the surgical site and within the anterior chamber during an ophthalmic procedure. Distal end  41  of sleeve  39  may include a pressure sensing transducer  83  for transmitting a feedback pressure signal via signal wires  85  to servo device  27  in order to control the pressure so that target tissue manipulation may be controlled. Signal wires  85  extend from the distal end to the proximal end of probe  23  for operatively coupling to handset  25  and servo device  27 . Similar to the tissue sensing circuitry embodiment, signal wires  85  may also be in a liquid-tight conduit located inside of the probe. It should be recognized that the pressure sensing transducer might also be located near the probe tip or in the irrigation pathway and in addition, may be located proximal to the tip along the probe within the anterior chamber. 
     Referring to  FIGS. 4 and 10 , servo device  27  may include a microprocessor circuit having associated operating software for reading the pressure signals and translating the signals into machine readable code. This may be accomplished with appropriate analog to digital converter devices, as is known in the art. Servo device  27  continuously monitors and regulates the pressure during an ophthalmic procedure, in particular a method of treating glaucoma. Referring to  FIG. 10 , in order to regulate pressure, in step S 101 , servo device processes pressure signals from pressure sensors  83 . In step S 103 , the pressure signals are compared with a desired reference pressures. In step, S 105  servo device  27  injects fluids, such as a viscoelastic fluid, into anterior chamber  7  of the eye in order to maintain the reference pressure or to adjust to a desired pressure level. In addition, in step, S 107 , servo device  27  may generate an error signal when the sensed pressure level becomes other than the desired reference level. Optionally, a pressure indicator display  62  may be located on handset  25 . Pressure sensor  83  may be located at a distal end of probe  23 . In addition, pressure sensor  83  may be located along the shaft of probe  23 . Optionally, more than one pressure sensor may be mounted on probe  23  at various locations. 
     Laser delivery system  21  may also include tissue recognition guidance circuitry for detecting penetration into Schlemm&#39;s canal by advancement of fiber-optic probe  23  or by laser energy. The tissue recognition guidance circuitry provides information regarding where the probe is located relative to target tissues. In one arrangement, as illustrated in  FIG. 11A , a form of optical spectroscopy is employed in which laser light pulses reflected from the target tissues create a back-scattered signal. Optical spectroscopy measures the interaction of light within tissues and provides information for diagnosis at the structural and pathophysiological level with intact tissues, as is known in the art. The back-scattered signal may be deflected off a dichroic mirror  87  in-line with an optical fiber  33  which may be the same fiber used to transmit the laser light or a separate detection fiber to an appropriate detector  89 . This enables precise identification of the spatial movement of the fluid, for example, from the anterior chamber to the interior of Schlemm&#39;s canal. Alternatively, as part of the optical spectroscopy, a separate optical fiber for returning the back-scattered signal to the detector may be employed. In either case, as is known in optical spectroscopy, the back-scattered signal provides information concerning the relative positions of the probe and the target tissues. Photoacoustic spectroscopy may be used in place of optical spectroscopy. In photoacoustic spectroscopy, incident light is modulated to generate acoustic frequencies. In either case, light signals may be reflected off the target tissue generating a signal reflecting the relative position of the probe to the target tissues. It should be noted that it may be possible to determine the location of the probe relative to target tissues by direct visualization though the primary and or accessory optical fibers. 
     In another arrangement, as illustrated in  FIG. 11B , a form of photoacoustic spectroscopy, which allows tissue imaging and depth profiling as is known in the art, implements an acoustic pulser  91  for transmitting signals along the probe  23  to a sensitive capacitive microphone  93  in order to sense the generated pressure fluctuations. The generated echo would be in a frequency range less than 50 KHz. The principles of photoacoustic spectroscopy are well known in opthalmology. 
     Referring to  FIG. 12 , laser delivery system  21  may further include motion controller  29  for enabling a controlled rectilinear movement of probe  23  into and through a target tissue site, such as the trabecular meshwork. This is achieved by blunting a portion of distal end  41  of probe  23  to enable sufficient contact against target tissues, such as the trabecular meshwork, with a controlled force produced by a mechanical or hydraulic apparatus. Motion controller  29  includes a limited motion driver  95 , such as one using a sensitive miniature voice coil, employed in handset  25  to move the blunt end of probe  23  against the tissues, such as the trabecular meshwork, at a controlled rate and through a precise distance. A force transducer system  97  senses the axial force applied to the tissues when a reactive resistance force is increased. The motion controller  29  slows probe movement when the tissues are compressed to a desired thickness. This type of automatic system provides precise controlled movement and operates more steadily than a manually operated probe. One skilled in the art would recognize various hydraulic or mechanical and controllable systems may be used for the purpose of moving probe  23  in a controlled movement. Motion controller  29  thus proves for controlled movement with micron precision. As illustrated in  FIG. 12 , precise controlled movement as provided with an automatic system is useful for compressing the trabecular meshwork  9 . 
     Distal end of fiber-optic probe  23  may include a device for viewing probe contact with target tissues. Such a device may have an optical fiber particularly used for viewing the target site, similar to that used in an endoscope that facilitates the viewing. A non-coaxial endoscope may also be used. Positioning can be detected by direct view, or by increasing the intensity of backscattered light or by interferometry. 
       FIG. 13  illustrates a method of facilitating the drainage of aqueous humor by creating a flow pathway via or circumventing the trabecular meshwork and juxtacanalicular trabecular meshwork, into Schlemm&#39;s canal of an eye in order to reduce intraocular pressure. Generally, a distribution of spaced apart radial passages in the periphery of the eye is established to assure relief of intraocular pressure. In step  201  of  FIG. 13 , the anatomic relationships of the target and adjacent tissues are analyzed. More specifically, anatomic landmarks are identified and relationships between those landmarks are noted. Available equipment employing ultrasonic spectroscopy and optical coherent tomography may be utilized for anatomic tissue localization both prior to and during the method. Once the anatomic factors are determined, the surgeon can visualize and study the position of the visible trabecular meshwork through a goniolens  97  and a typical operating microscope used in ophthalmic surgery. The surgeon is ready to continue with the procedure once landmarks are identified, including Schwalbe&#39;s line, the scleral spur and possibly Schlemm&#39;s canal. 
     Referring to  FIGS. 3 and 13 , in step  203 , a small self-sealing incision or paracentesis opening  14  is made in the cornea  15  or sclera  17  to allow access to the target site. The small size of the initial opening in the cornea or the sclera introduces a minimal entry trauma, and the small size facilitates self-closure without suturing in most instances. In step  205 , the anterior chamber is stabilized with viscoelastic and fiber optic probe  23  is advanced into the opening  14  and into anterior chamber  7 . At step  207 , probe  23  is advanced through the anterior chamber according to transocular movement to position distal end  41  of probe  23  in contact with or adjacent to trabecular meshwork  9 . A determination of whether probe  23  should be in contact with or adjacent to trabecular meshwork  9  depends on the physical characteristics of the particular site and is made by the surgeon and is within ordinary skill in the art. For the purpose of the present invention, the probe  23  should be within an operable limit of the trabecular meshwork, that is, it should be in contact with or adjacent to the trabecular meshwork in order to enable photoablation at the target tissues, as determined by one of skill in the art. 
     In step  209 , a desired target area is identified so as to position distal end  41  of probe  23  in a direction relative to Schlemm&#39;s canal  11  in order to penetrate its inner wall adjacent to the anterior chamber. Positioning distal end  41  of probe  23  will depend on the energy distribution of the selected probe tip  47 . As previously described, numerous probe tip designs may be used, depending on need. Several techniques may be used to identify the desired target tissues. In one technique, if Schwalbe&#39;s line  18  ( FIG. 8 ) is visible, then a measurable reference exists that may be used to relate to the length of sleeve  24  at its distal end. More specifically, probe  23  may be positioned at the identified anatomic landmark, such as Schwalbe&#39;s line  28 . Alternatively, a radial indicator, such as a spur or other marker/spacer, extending radially from sleeve  39  distal end  41  but designed to enter at the opening  14  may also be employed. Yet another alternative, includes utilizing a coaxial endoscope located near the distal tip for viewing the trabecular meshwork  9  and resultant positioning distal end  41  of probe  23 . An endoscope may also be used through a separate self-sealing incision. In another alternative, an ultrasound detector or scanner may provide a graphical representation of the tissue anatomy and position of distal end  41  of probe  23  to allow locating the distal end with precision relative to Schlemm&#39;s canal, as in A scan ultrasonograph or ultrasonic biomicroscopy. Ultrasonic biomicroscopy is the technology in which high frequency ultrasound (40-100 MHz) is used to produce images of biological structures with resolution approaching 20 micrometers. The structures of interest must be located within 4 mm of the surface of the body or be accessible by an endoscope because of increased loss of ultrasound at high frequencies. Regardless of technique used, a landmark, such as Schwalbe&#39;s line, is identified. Next, the energy distribution of a selected probe tip  47  is identified. The probe  23  is then applied to the identified landmark so that photoablative energy may be applied from probe tip  47  in a manner applicable to the target tissues. 
     At step  211 , the intraocular pressure may also be monitored by pressure sensor  83  at distal end  41  or at an intraocular portion of the probe  23 . Alternatively, an external pressure sensor or transducer may be used to monitor the internal pressure in the stabilized anterior chamber within desired limits. At step  213 , the control switches may be operated by the surgeon to arm the laser for firing into the target site. 
     Optionally, as shown in step  215 , the trabecular meshwork  9  may be compressed or flattened to a general thickness of about 90 microns to reduce the amount of laser radiation and increase treatment rate. Compression of the meshwork reduces the distance of penetration through the trabecular meshwork from approximately 150 microns to about 90 microns, before the distal end  41  of probe  23  reaches Schlemm&#39;s canal. Because each light pulse ablates about 1 or 2 microns of tissue when using a 308 nm excimer laser, the time and number of pulses used for micropenetration is shortened and precision is increased. Compaction also aids in physically stabilizing the meshwork. This compaction causes the number of pulses needed in order to penetrate the meshwork and thus enter Schlemm&#39;s canal to range from 10 to 100 pulses for the ultraviolet wavelengths. While in the infrared wavelengths, 1 to 20 pulses typically may be sufficient to penetrate into Schlemm&#39;s canal. 
     With reference to step  215 , a number of approaches may be used to compress the trabecular meshwork at the target site. As shown in  FIG. 9 , one approach includes physically contacting and applying an axial force so that the distal end of probe  23  being blunted pushes against the meshwork. Tissue contact sensor  73  may provide appropriate notification of the tissue-contact of probe  23 . During the advance of the probe into the meshwork, the surgeon may physically view the compaction of the meshwork using the previously described ultrasound scanner, endoscope, or other viewing systems of the eye anatomy. 
     In an alternative approach, the viscoelastic fluid of a selected viscosity and molecular size may be used to flatten the trabecular meshwork. Incremental or stepped pressure induced within the eye may be achieved by injecting the viscoelastic fluid from irrigation control  55  by control switches or buttons disposed in handset  25 . In the viscoelastic fluid case, the surgeon slowly increases the pressure until the meshwork compresses to a desired thickness. It should be recognized that servo device  27  may also be employed to increase the pressure automatically by feedback of pressure sensor  83  in the manner shown in  FIG. 10 . 
     Whether or not the meshwork is compressed, as shown in step  217 , laser unit  31  transmits laser energy via fiber optic probe  23  so as to photoablate the juxtacanalicular trabecular meshwork and inner wall of Schlemm&#39;s canal in the target site. Optionally, concurrent with activation of the laser (see step  217 ), the irrigation fluid and/or viscoelastic fluid may be supplied into target site of laser energy application. Also, as shown in step  219 , while photoablative laser energy is applied to the target site, irrigation fluid and/or vaporized gases may be aspirated in the region of light energy impingement via the aspiration flow path  51  in fiber optic probe  23 . The operation of aspiration control  57  and associated flow path has been previously described. 
     As an alternative to irrigation fluid, therapeutic agents may be injected into the anterior eye chamber or into Schlemm&#39;s canal at or about the same time as photoablation is being carried out to thereby minimize traumatic effects and oppose self-healing tendencies of the eye anatomy. In addition to or separately from anti-inflammatory agents, both steroidal and non-steroidal anti-fibroblastic agents and anti-angiogenic agents, singly or in combination can also be provided. The concurrent application of therapeutic agents advantageously increases the long term benefits of opening the meshwork and Schlemm&#39;s canal. It should be recognized that once an opening is created in Schlemm&#39;s canal from the fiber-optic probe, the therapeutic agents may be injected into the opening. Specific examples of these types of agents include DFU, which is a nonsteroidal anti-inflammatory, anecortave acetate which is one of the angiostatic steroids, and anti-TGF which is a monoclonal antibody known to inhibit the activity of all three forms of TGF-.beta. in vivo. 
     Optionally, as shown in step  221 , the distal tip  41  of probe  23  may be advanced inwardly during the photoablation of the tissues and, if the meshwork was flattened, there may be relative movement as the meshwork expands around the aperture. Any resultant relative movement may be measured at step  221  and the results of the measurement may provided in a feedback loop to handset  25  to be used to control further movement of the probe  23 . A pilot opening may be created into Schlemm&#39;s canal. Agents then may be injected into Schlemm&#39;s canal causing it to expand such that subsequent openings will be less likely to injure the outer wall. More specifically, in order to protect the outer wall of Schlemm&#39;s canal, which should not be punctured, a pilot hole may be created and Schlemm&#39;s canal inflated. The pilot hole may be stented, creating a barrier. A device known as a trabeculatome may be used as such a barrier. The pilot hole may be created and the and stent inserted from a site internal or external to the eye. 
     While a skilled surgeon may operate fiber optic probe  23  to penetrate only the proximal inner wall of Schlemm&#39;s canal, once in the canal, the distal outer wall should be not penetrated. Creating a passageway into Schlemm&#39;s canal should be of a controlled depth, because penetration too great a depth could be more traumatic to a patient, due to contact with or breaching of the distal wall of the canal. 
     Optionally, as shown in step  223 , detection of penetration of the proximal inner wall of Schlemm&#39;s canal may be accomplished in a number of approaches. A first approach is optical, i.e., by transillumination; another approach includes viewing an ultrasound scanned image of the target site from an above plan view orientation, e.g., high frequency ultrasound. In a second alternative approach to detect penetration of the proximal inner wall, a chemical or photochemical detection method may be implemented. In this case, for example, a hemoglobin detector is employed to determine that blood flow has been encountered in Schlemm&#39;s canal. This may be performed, for example, by optical spectroscopy of oxygenated and deoxygenated hemoglobin, i.e., by using diffused light from red diode absorption (e.g., pulse oxymetry, a common clinical tool). As an alternative to a hemoglobin detection, a sensor, for example, optical spectroscopy detecting fluorescence by illuminating and detecting substances directly or by fluorescent stimulation, may detect the presence of a marker substance (e.g. a fluorescing dye), which may be added to the viscoelastic material injected into Schlemm&#39;s canal. Examples of such marker substances include fluorescine, indocyanine green or trypan blue. A third alternative approach is to implement the aforementioned tissue recognition guidance circuitry of laser delivery system  21 . 
     As shown in step  225 , once penetration of the proximal wall has been detected, the probe  23  is withdrawn before the distal wall is penetrated. In step  227 , probe  23  is repositioned at an accessible new target site for repetition of the sequence. The probe is subsequently moved transocularly to a number of different angular locations about the corneoscleral angle shown in  FIG. 2 , in order to create additional radial passages in the periphery of the eye, as previously described. As a result, an adequate number of radial outflow apertures, typically ranging from two to ten, are formed in the juxtacanalicular trabecular meshwork  9  and the proximal inner wall of Schlemm&#39;s canal  11 . The inner proximal wall of the resultant microsculptured Schlemm&#39;s canal will have precisely cut or minimally fused ends of tissue as a result of the process described above. Minimal scarring or shearing of tissue will occur so as to discourage initiation of a significant healing response and to provide for controlling and lowering the intraocular pressure for a longer time as compared with previously used techniques. 
     In an alternative embodiment of the method, once Schlemm&#39;s canal is penetrated, in step  229 , as illustrated in  FIG. 14 , an appropriate viscoelastic fluid may be injected or coaxially infused so as to inflate or expand the canal. Thereafter, once the probe is repositioned to a new target site, a greater margin of error for photoablation exists to avoid damaging the outer wall. In addition, filling Schlemm&#39;s canal with viscoelastic fluid results in a compression of the trabecular meshwork from behind such that, when the meshwork is compressed to lessen the thickness of the trabecular meshwork to be ablated and, in addition, the inner and outer walls of Schlemm&#39;s canal stay separated and are prevented from collapsing by the axial compressive force applied by probe  23 . In addition, filling Schlemm&#39;s canal prevents penetrating the outer wall by providing a larger distance of about 300 microns between the inner and outer walls. It should be recognized that a viscoelastic fluid having therapeutic agents may also be used to expand Schlemm&#39;s canal. This use has multiple benefits such as creating a pressure reaction structure, a larger target site to photoablation, preventing penetration of the distal wall of Schlemm&#39;s canal, and applying therapeutic agents in all the openings or perforations in a uniform manner. It should be recognized that expansion of Schlemm&#39;s canal will usually not have to be repeated once performed. In an alternative, once Schlemm&#39;s canal is penetrated, a blocking device such as a tube, stent or viscoelastic material may be placed into Schlemm&#39;s canal to prevent injury to its outer wall. This device may also be introduced into Schlemm&#39;s canal from outside of the eye via a separate incision. 
     Referring now to  FIGS. 15-18B , devices and a technique are shown for controlling the geometry of Schlemm&#39;s canal  11  and optionally the trabecular meshwork  9 . Referring to  FIG. 15 , an intraocular implant device  99  is illustrated. Implant device  99  self-retains in the inner wall of Schlemm&#39;s canal  11  and may extend into and through the trabecular meshwork  9 . Implant device  99  may be embodied in a stent having an elongated tubular body  101 . Implant device  99  may include a valve leaflet to ensure unidirectional outflow. The distal end of tubular body  101  may include a plurality of foldable legs  103  for engaging the inner wall of Schlemm&#39;s canal when they are fully deployed. The proximal end of tubular body  101  includes a flange portion  105  and a plurality of thin elongated cylindrical projections  107  having hook-like distal ends  109  for linking or hooking into the trabecular meshwork  9 . 
     Tubular body  101  may have an inner diameter dimension of 10-200 microns and an outer diameter of less than 1000 microns. Foldable legs  103  typically are in a range from 5 to 50 microns. Cylindrical projections  107  may have dimensions in a range from 5 to 50 microns and appear similar to hooks of Velcro which self-engage and self-retain. Implant device  99  preferably may be constructed from a biocompatible, inert material capable of being sterilized and unlikely to stimulate a foreign body reaction. Tubular body  101  may be constructed from materials such as thermoplastic, stainless steel, PMMA, nylon or polypropylene. Foldable legs  103  and cylindrical projections  107  can be made from one of these same or other materials. With reference to  FIG. 16 , an alternative implant device  100  is illustrated. Device  100  may be similar to the structure of device  99 , except that the tubular body extends only the thickness of the inner wall of Schlemm&#39;s canal. 
     An embodiment of a system and method of positioning the implant device is illustrated in  FIG. 17 . A self-sealing opening is created in the cornea of the eye. A cutting cannula or fiber-optic probe  23  may be inserted and advanced transocularly through the anterior chamber to open a cylindrical aperture  111  extending from trabecular meshwork  9  to Schlemm&#39;s canal  11 . This cannula or the probe may then be withdrawn from the eye. Implant device  99  is retained or carried inside a distal end of an inserter device  113 . Such configuration enables the distal end of implant device  99  having foldable legs  103  to be positioned for eventually implantation into aperture  111  and Schlemm&#39;s canal  11 . The proximal end of implant device  99  abuts a central shaft or plunger member  115 . Central shaft  115  is slidably engaged within inserted tube  113 . Next, the distal end of inserter tube  113  having implant device  99  is introduced through the opening and advanced to cylindrical aperture  111 . Thereafter, the surgeon may position the distal end of inserter tube  113  such that implant device  99  is inserted into the aperture. 
     Once the implant device is in the aperture  111 , central shaft  115  may be advanced forward to push the distal end of implant device  99  into and through the inner wall of Schlemm&#39;s canal  11 . Foldable legs  103  are then unrestrained and released into the proximal inner wall of Schlemm&#39;s canal  11 . The inserter tube and central shaft are withdrawn from the aperture. At this point the cylindrical projections of the proximal end of implant device engage the trabecular meshwork  9 . If desired, as shown in  FIG. 18A , a feeder tube  117  may abut within the proximal opening of the tubular body and various therapeutic agents or viscoelastic fluids may be provided into the canal. Alternatively, as shown in  FIG. 18B , an implant device may be eliminated and feeder tube  117  may be inserted into Schlemm&#39;s canal  11  to inject fluids. Nevertheless, it should be recognized that an implant device might be inserted in each aperture created in the trabecular meshwork  9 . A grommet unit may be employed instead of a stent, and either may incorporate a one way valve. It should be recognized that inserter device may be configured with circuitry similar to fiber-optic probe  23 . For example, distal end of inserted tube  113  may include a tissue-contact sensor to detect when the meshwork is contacted by tube  113 . 
     The system and method of treatment for glaucoma should account for variations in the relative position and character of Schlemm&#39;s canal as well as anatomical differences in the trabecular meshwork from patient to patient. It should be recognized that other alternatives may present themselves to those skilled in the art. Fabrication techniques used for miniaturized devices may be employed to form sensors, actuators and conductors on the inserted portion of a probe. The probe may be designed so that it is disposable wholly or in major part. The tip end of the probe may be angled to or deflect off a small mirror or prism according to the angle of the trabecular meshwork. A variety of other types of irrigation and aspiration can be used with the probe to perform the function described. For example irrigation fluid may be fed in between the outside of the metal sleeve and the inner surface of a concentric shield that conforms to and seals the incision or via a separate incision. 
     While the invention has been described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the scope thereof. For example, a microdrill may be used employed instead of a fiber optic probe to penetrate the trabecular meshwork and Schlemm&#39;s canal. Also it should be recognized that the concept of compressing the eye anatomy with viscoelastic material is applicable to other tissues such as joint cartilage, ligaments, arachnoid tissue and the like and fiberoptically introduced photoablation of these tissues to effect pressure control and tissues removal for alterations of tissue structure, fluid flow and placement of devices such as stents or anchors. The techniques described in the present invention may be used as an adjunct to current endoscopic surgical procedures. More specifically, tissues may be identified endoscopically and photoablated as previously described according to the present invention. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.