Abstract:
A system and its method for creating a microchannel in the trabecular meshwork of an eye include a laser unit for generating a laser beam, and an imaging unit for creating an image of the trabecular meshwork. The system also includes a computer which defines the microchannel. A comparator that is connected with the computer then controls the laser unit to move the focal point of the laser beam. This focal point movement is accomplished to create the microchannel, while minimizing deviations of the focal point from the defined microchannel.

Description:
[0001]    This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/550,286, filed Oct. 21, 2011. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention pertains generally to systems and methods for performing ophthalmic surgical procedures using laser devices. More particularly, the present invention pertains to systems and methods for surgically relieving Intraocular Pressure (IOP) to prevent glaucoma. The present invention is particularly, but not exclusively, useful as a system and method for creating microchannels through the trabecular meshwork or through the iris to thereby avoid using mechanical “shunts” and/or “stents” in the eye for the treatment of glaucoma. 
       BACKGROUND OF THE INVENTION 
       [0003]    Schlemm&#39;s canal is a circular channel in the eye that is located in corneal/scleral tissue at the juncture between these two tissues. Schlemm&#39;s canal surrounds the cornea, and its functionality is essentially two-fold. For one, it collects aqueous humor from the anterior chamber of the eye. For another, it takes the aqueous humor that is collected from the anterior chamber and delivers it through anterior ciliary veins to the bloodstream. The net effect of this transfer of aqueous humor from the eye to the bloodstream is to control the intraocular pressure (IOP) inside the eye. 
         [0004]    Located between Schlemm&#39;s canal and the anterior chamber of the eye is the trabecular meshwork. From a fluid flow perspective, the trabecular meshwork is intended to control the outflow of aqueous humor from the anterior chamber. It happens, however, that resistance to this outflow can be substantially aggravated (i.e. increased) for various reasons. When this happens, an unwanted consequence is an increase in IOP, and the possibility of an onset of glaucoma. 
         [0005]    A complication that can contribute to an increase in IOP and glaucoma occurs when a fluid flow restriction develops between the iris and the crystalline lens. Typically, this occurs when the gap between the iris and lens closes or is otherwise obstructed. This may be further aggravated by a narrowing of the region around the trabecular meshwork. 
         [0006]    Heretofore, one of the standard treatments for glaucoma has been the placement (implantation) of mechanical shunts or stents into the trabecular meshwork. Specifically, this has been done for the purpose of using the shunts or stents as fluid flow conduits for relieving IOP. These mechanical devices, however, are perceived by the body as foreign objects. And the body responds accordingly. One short term effect of the body&#39;s response is that the IOP is actually reduced somewhat. It is, however, only a short term effect. In the longer term, these mechanical devices have been generally ineffective for their intended purpose. 
         [0007]    In light of the above, it is an object of the present invention to provide a system and method for creating microchannels in the trabecular meshwork between the anterior chamber and Schlemm&#39;s canal that will improve the outflow of aqueous humor from the anterior chamber, to thereby prevent the onset of glaucoma. Another object of the present invention is to create microchannels through the iris to improve fluid flow from the posterior chamber into the anterior chamber to help prevent the onset of glaucoma. Yet another object of the present invention is to provide a system and method for creating microchannels in the anterior portion of an eye to prevent the onset of glaucoma, wherein the microchannels are created by Laser Induced Optical Breakdown (LIOB) to thereby avoid the implantation of foreign mechanical objects in the eye. Still another object of the present invention is to provide a system and method for creating microchannels in an eye that are easy to use, are simple to implement and are comparatively cost effective. 
       SUMMARY OF THE INVENTION 
       [0008]    In accordance with the present invention, a system and method are provided for creating a microchannel through the trabecular meshwork or the iris of an eye to interconnect the anterior chamber and the posterior chamber of the eye in fluid communication with Schlemm&#39;s canal. The purpose of the microchannel(s) is to enhance the functionality of Schlemm&#39;s canal by improving the outflow of aqueous fluid from the eye. A consequence of this is the lowering of intraocular pressure (IOP) in the eye. In operation, each microchannel is created by using a laser to perform LIOB in the target tissue (i.e. the trabecular meshwork and/or the iris). Thus, for the present invention LIOB is employed rather than having to introduce mechanical objects into the eye for the intended purpose. It is an important aspect of the present invention that the microchannel(s) are created by a computer controlled laser, wherein the control reference is provided by Optical Coherence Tomography (OCT). 
         [0009]    Structurally, the system includes a laser unit for generating and directing a pulsed, femtosecond laser beam along a laser beam path to a focal point. The system also includes an imaging unit that is used for creating a three dimensional image of the trabecular meshwork. Preferably, as indicated above, this imaging unit is an Optical Coherence Tomography (OCT) device of a type that is well known in the pertinent art for the intended purpose. Further, the system includes a computer that is interconnected to both the laser unit and the imaging unit. 
         [0010]    As intended for the present invention, a computer program defines the microchannel(s). Specifically, this computer program includes information about the location and dimensions of the intended microchannel(s). Further, the computer program establishes where each microchannel will be located and positioned to interconnect the posterior and anterior chambers of the eye in fluid communication with Schlemm&#39;s canal. In detail, a microchannel may be a complete channel that passes through either the trabecular meshwork or the iris. In the specific case of the trabecular meshwork, the microchannel may alternatively be a partial channel that extends only part way into the trabecular meshwork. Also, in the case of the trabecular meshwork, instead of a microchannel, the laser may be used to only heat the tissue for stimulating fluid flow. In the event, any combination of the above stated possibilities can be employed. 
         [0011]    During the creation of a microchannel, a comparator that is connected to the imaging unit and to the computer uses information from the computer program to determine whether there is an actual operational deviation of the focal point from the defined microchannel(s). If so, an error signal that is indicative of the deviation is generated, and the focal point of the laser beam is moved to minimize the error signal. In this manner, the focal point of the laser beam is guided by the computer program to alter target tissue in the anterior portion of the eye by Laser Induced Optical Breakdown (LIOB), to thereby create the microchannel(s). 
         [0012]    In one embodiment of the present invention, a gonioscope can be used for guiding the laser beam. If used, the gonioscope will include a contact lens that is structurally connected to the laser unit. Also, there will be a deflecting mirror that is mounted on the contact lens for directing the laser beam path toward the trabecular meshwork. Alternatively, it is also envisioned that the laser beam path can be directed to the trabecular meshwork directly through the sclera of the eye. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which: 
           [0014]      FIG. 1  is a schematic presentation of a system in accordance with the present invention shown in its operational relationship with an eye, which is shown in cross section; 
           [0015]      FIG. 2  is an enlarged view of the anterior chamber angle of an eye, as shown surrounded by the line  2 - 2  in  FIG. 1 ; 
           [0016]      FIG. 3A  is a representation of a complete microchannel shown passing through the trabecular meshwork in accordance with the present invention; 
           [0017]      FIG. 3B  is a representation of a partial microchannel shown passing part way through the trabecular meshwork in accordance with the present invention; 
           [0018]      FIG. 4  is a functional block diagram of a closed-loop control system incorporating components of the present invention; 
           [0019]      FIG. 5A  is a cross-sectional view of an eye (as seen in  FIG. 1 ) showing a laser beam passing through the sclera of an eye and into the trabecular meshwork of the eye for creation of a microchannel; and 
           [0020]      FIG. 5B  is a cross-sectional view of an eye (as shown in  FIG. 5A ) showing a laser beam being directed by a gonioscope into the trabecular meshwork of the eye for creation of a microchannel. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    Referring initially to  FIG. 1 , a system for creating microchannels in the anterior portion of an eye is shown and is generally designated  10 . As shown, the system  10  includes a laser unit  12 , an imaging unit  14  and a computer/comparator  16 . In the system  10 , the imaging unit  14  is operationally connected to the computer/comparator  16 , and the computer/comparator  16  is connected directly to the laser unit  12 . With this combination, the system  10  is used to generate and direct a laser beam  18  toward an eye  20  for an ophthalmic surgical procedure as envisioned for the present invention. 
         [0022]    For the purposes of the present invention, the laser unit  12  is capable of generating a so-called “femtosecond” laser beam  18 . Thus, the generated laser beam  18  includes a sequence of laser pulses having a very ultra-short duration (e.g. less than approximately 500 fs). Importantly, the laser beam  18  must be capable of performing Laser Induced Optical Breakdown (LIOB) on selected target tissue inside the eye  20 . Further, it is important for there to be a precise performance of this LIOB. Such precision requires there be a capability of imaging the target tissue that is to be altered by LIOB. 
         [0023]    The imaging unit  14  is preferably a type of device that operates using Optical Coherence Tomography (OCT) techniques. Thus, the imaging unit  14  will include a light source to generate an imaging beam  22  and optics to direct the imaging beam  22  toward the eye  20 . In this case, the imaging beam  22  is used to create three dimensional images of selected tissues within the eye  20 . As indicated in  FIG. 1 , these images are then passed to the computer/comparator  16  for use by the computer/comparator  16  in controlling the laser unit  12 . As envisioned for the present invention, the precision required for this control will be best appreciated with reference to  FIG. 2 . 
         [0024]    In  FIG. 2 , the anterior chamber angle and its adjacent anatomical features of the eye  20  are shown. In particular,  FIG. 2  identifies the cornea  24  and the sclera  26  of the eye  20 . It also identifies the anterior chamber  28  of the eye  20  and the trabecular meshwork  30  that interconnects the anterior chamber  28  with Schlemm&#39;s canal  32 . In a normal eye  20 , aqueous from the anterior chamber  28  passes through the trabecular meshwork  30  and into Schlemm&#39;s canal  32 . From there, the aqueous is returned to the bloodstream. For various reasons, however, this process may be impeded by tissue structures in the eye  20 . If this happens, as envisioned for the system  10  of the present invention, a microchannel  34 , or a plurality of microchannels  34 , can be created through target tissue in the anterior portion of eye  20  to alleviate this condition (e.g. the onset of glaucoma). 
         [0025]    Several situations are of particular interest for the present invention. For one, there is interest in establishing a fluid flow capability from the anterior chamber  28 , out through the trabecular meshwork  30  and into Schlemm&#39;s canal  32 . In this case a laser trabeculoplasty procedure is envisioned wherein microchannels  34  are established into or through the trabecular meshwork  30 . Also, a fluid flow capability from the posterior chamber  29  and into the anterior chamber  28  is of interest. Specifically, this additional concern arises when the gap  31  between the iris  33  and the crystalline lens  35 , which normally allows for fluid flow, is closed or otherwise becomes occluded. In this case, microchannels  34  may need to be created through the iris  33  in an iridotomy procedure. If required, this will be done to establish fluid flow through the iris  33  from the posterior chamber  29  into the anterior chamber  28 . 
         [0026]    For purposes of the present invention, microchannels  34  can be employed for either a laser trabeculoplasty procedure or for an iridotomy procedure. With regard to a laser trabeculoplasty procedure, a microchannel  34  can be configured as either a complete microchannel  34  (see  FIG. 3A ), which passes completely through the trabecular meshwork  30 ; or as a partial microchannel  34 ′ (see  FIG. 3B ) which passes only part way through the trabecular meshwork  30 . In either case, the diameter “d” of the microchannel  34  or  34 ′ will be somewhere in a range between about one hundred microns and approximately four hundred microns (“d”=100 μm→400 μm). Also, the sidewalls of the microchannel  34 ,  34 ′, are typically to be burnt in order to prevent closure. Additionally, instead of creating either a complete or a partial microchannel  34 , the trabecular meshwork  30  can be heated to stimulate fluid flow through the trabecular meshwork  30 . On the other hand, with regard to an iridotomy procedure, a complete microchannel  34  is typically required through the iris  33 . 
         [0027]      FIG. 4  indicates that the system  10  is intended to be computer-controlled and operated with closed loop feedback. For this operation, a computer program  36  is provided for use with the computer/comparator  16 . Specifically, the computer program  36  will include a definition for each of the microchannel(s)  34  that are to be created in the trabecular meshwork  30 . This definition will necessarily include the location and the dimensions of each microchannel  34 . As envisioned for the present invention, there may be a need for a plurality of such microchannels  34 . For example, looking down onto a plan view of the eye  20 , it may be desirable to create individual microchannels  34  at, for example, the 2, 4, 8 and 10 o&#39;clock positions. For both procedures (laser trabeculoplasty and iridotomy), the microchannel  34  ( 34 ′) can extend through arcs of 180° to 360°. In any case, in order to establish a location for the microchannel  34 , as well as for other laser functions, the computer program  36  provides a reference input  38  for the system  10 . 
         [0028]    In the operation of system  10 , the reference input  38  from the computer/comparator  16  (i.e. computer program  36 ) is sent to a summing point  40 . It is then sent from the summing point  40  as an actuating signal  42  for the laser unit  12 . Thus, the laser beam  18  is generated as an output from the laser unit  12  in accordance with the actuating signal  42 . For guidance and control purposes, the output of the laser unit  12  (i.e. laser beam  18 ) is monitored by the imaging unit  14 . Further, the imaging unit  14  creates three dimensional images that show the effects of LIOB in the trabecular meshwork  30 . These images are then used as the basis for generating feedback (error) signals  44  that are returned to the summing point  40 . At the summing point  40 , the reference input  38  (i.e. definition of microchannel  34 ) is compared with the feedback (error) signal  44  (i.e. images from the trabecular meshwork  30 ). This comparison is then used to appropriately adjust the actuating signal  42 . As with any closed loop feedback control system, the objective here is to maintain the feedback (error) signal  44  at a null. 
         [0029]    Different methods for employing the system  10  are shown in  FIG. 5A  and  FIG. 5B . In  FIG. 5A , it is shown that the laser beam  18  can be sent directly through the sclera  26  for LIOB in the trabecular meshwork  30 , while the eye  20  is being stabilized. In this case, it may be necessary to hydrate the sclera  26  with topical ointments or injections in a manner that will make the sclera  26  effectively transparent during a procedure. On the other hand, as shown-in  FIG. 5B , a gonioscope  46  may be used. As shown, in this alternative method for using system  10 , the gonioscope  46  will include a contact lens  48  which can be connected with the laser unit  12  to stabilize the eye  20 . It will also include a deflecting mirror  50  that will direct the laser beam  18  onto the trabecular meshwork  30  where the microchannel  34  is to be created by LIOB. 
         [0030]    While the particular System and Method for Lowering IOP by Creation of Microchannels in Trabecular Meshwork Using a Femtosecond Laser as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.