EP0464138A1 - Non-invasive sclerostomy laser apparatus and method - Google Patents

Abstract

In a non-invasive treatment of glaucoma, part of the sclera is stained iontophoretically with a dye having absorption at a wavelength at which the cornea of the eye is particularly transmitting. Radiation from a synthesizable coloring laser is specifically synthesized on the absorption of the dye for ablation. The dye applied by iontophoresis crosses the conjunctiva and enters the sclera to identify a region on which a relatively high power dye laser radiation is sent through a goniolens. The high power beam is directed using a low power aiming laser beam coupled in the same optical path as the radiation from the coloring laser and supplied via a conical split fiber optic lamp delivery system. The laser produces pulses between 75 and 750 millijoules, lasting from 1 to 30 microseconds, preferably about 10 microseconds. A point of 100 to 300 microns is illuminated.

Description

NON-INVASI E SCLEROSTOMY LASER APPARATUS AND METHOD

Background of the Invention

This invention relates to methods for treatment of glaucoma by use of a laser to create a perforation, or fistula, in a sclera.

Glaucoma is a potentially debilitating disease of the eye in which the intraocular pressure of fluid within the eye rises above normal levels. It is recognized that, by creating a fistula in the sclera at the peripheral regions of the cornea, the fluid pressure associated with glaucoma can traverse the sclera to the subconjunctival space where it is gradually absorbed or translocated away from the interior of the eye. Laser light has been used to create such a fistula. For example, in 1969

L'Esperance increased absorption of the sclera in the visible region by injection of Indian ink to allow use of a continuous wave argon ion laser to create a scleral hole. L'Esperance "Laser Trabeculosclerosto y in Ophthalmic Lasers:

Photocoagulation, Photoradiation, and Surgery," St. Louis: C.V. Mosby Co., 538-543, 1969. In addition, Latina et al. proposed the development of an ab interno laser sclerostomy using a goniolens technique. Latina et al., ARVO Abstract, p. 254, No. 12, 1986. Methylene blue was applied iontophoretically to scleral stips from enucleated eyes, and the sclera was then ablated by use of one microsecond-long dye laser pulses at 660 nanometers delivered through a 600 micron optical fiber.

Ablation was observed at 50 miUijoules per pulse. The authors stated that the "potential of this technique for clinical use is being investigated. "

In 1987, Latina et al, ARVO, No. 11, described ab interno scleral ablations using one microsecond-long pulses at energies of between 30 and 40 miUijoules per pulse. The conjuctiva which covers the sclera was raised in that local region with salt solution to avoid inadvertent puncture of the conjunctiva with subsequent ablation of the sclera. An optical fiber was inserted through the cornea at the opposite side of the eye and passed through the anterior chamber and placed in contact with the sclera at the dyed site. One microsecond laser pulses of 660 nanameter wavelength were delivered through the 320-micron diameter optical fiber. Seven to twelve pulses were applied using energies of 30 to 40 miUijoules per pulse. Such invasive systems are undesirable because of the attendant problems of introducing infection and inflammation through invasive surgery, the healing problems associated with an invasive procedure and the difficulty in maintaining the scleral fistula in an open condition. Latina et al. did propose a non-invasive procedure using a slit lamp and goniolens.

Summary of the Invention

In accordance with the teaching of the present invention, a totally non-invasive glaucoma treatment procedure is disclosed. A laser produces pulses of light of at least 75 miUijoules per pulse and of between about 1.0 and 30 microseconds duration. The light is noninvasively focused, as by a goniolens, through the cornea onto the sclera. The sclera is illuminated at a spot of between 100 and 300 microns diameter.

More specifically, a region of the sclera is iontophoretically dyed. A tunable dye laser or other laser such as a ruby laser of relatively high power, and operative to produce maximum energy transmission through the cornea with minimal absorption there, has its delivery path aimed through a goniolens to the dyed portion of the sclera. A slit lamp delivery system is utilized to provide aiming and pulsed laser application. The pulsed laser causes ablation of the sclera in the dyed portion, opening a fistula for relief of ocular fluid pressure. In a particular implementation, a visibly absorbing dye such as methylene blue is delivered through an iontophoresis probe applied to the periphery of the cornea. Iontophoretic dye is transferred through the conjunctiva into a region of the sclera through which a fistula is to be developed. Most preferably, the dye is water soluble, non-toxic and ionized or charged in solution. A laser of wavelength of about 590 nanometers maximizes absorption at the peak of the dimer of methylene blue diluted in the sclera. Other wavelengths of between 550 and 700 nanometers may be used. For example, the 694 nanometers wavelength of a ruby laser is at the wings of the absorption curve. A slit lamp delivery system includes an operator viewing path which is directed into and sideways through the cornea by a goniolens to a point on the sclera which has been dyed iontophoretically. The slit lamp delivery system includes a beam splitter in the viewing path so that radiation from a high power laser beam from a dye laser, tuned to the absorption wavelength of the iontophoretically applied dye, can be coupled into the viewing path. A low power aiming laser, such as a helium neon laser, has its output beam first applied along the same path as the high power dye laser and functions as an aiming laser.

The operator, using adjustments in the slit lamp delivery system or the goniolens, positions the low power aiming laser beam at the dyed location of the sclera where the fistula is to be created. Then, with switching of a shutter, pulsed radiation from the high power laser is applied to the same point to achieve ablation of the scleral tissue until a fistula has been opened to allow ocular fluid flow from the inner eye to the subconjunctival space.

It is preferred that a fiber having a distal diameter of about 100 to 300 microns, and preferably less than 200 microns, be used to create a spot size on the sclera of between 100 to 200 microns without demagnificaton. Demagnification would result in a larger cone angle, and the cone angle should be held to less than about 20^* so that the site at the limbus being illuminated is not shadowed in the angle. The cone angle is best held above 8^* to avoid high power density at the cornea. A range of 8" to 15^* is preferred, and of 10^* to 13^* is most preferred. It has also been found that best results are obtained with pulse durations of greater than one microsecond, preferably greater than 3 microseconds and most preferably greater than 5 microseconds. Durations of less than 25 microseconds are preferred, most preferably less than 20 microseconds. Durations of about 10 microseconds are best. The energy per pulse is best between 75 and 750 miUijoules. Low energies in the range of 75-250 miUijoules can be used successfully with pulse repetitions such as from 10 to 15 pulses. Energies of 150-500 miUijoules allow for use of only one or a few pulses.

Given these parameters of short pulse width, small diameter and high energy, a conventional fiber is subjected to a great deal of wear from the beam entering the proximal end of the fiber. To minimize that wear by minimizing the power and energy density at the proximal end, a tapered fiber has been used to deliver the laser beam from the laser to the slit lamp assembly. A taper from 600 microns to 200 microns, or from 300 microns to 100 microns, over a length of one meter has been found acceptable.

This invention provides a non-invasive method for ablating a small section of sclera with minimal damage to surrounding tissue. The laser light has a set of parameters that minimizes damage to surrounding tissues and prevents potentially harmful acoustical effects of the laser light. Because no incision is required, the number of complications inherent in the surgery is minimized. In addition, the level of fibroblast proliferation, and thence subconjunctival scars, is reduced, and permanency of the ablated area is increased.

Brief Description of the Drawing

These and other features of the present invention are more fully described below in the solely exemplary detailed description and accompanying drawing of which the figures illustrate a system and associated method for non-invasive glaucoma pressure relief.

Figure 1 is a schematic illustration of the system including the lasers, slit lamp assembly, geniolens and iontophoresis probe.

Figure 2 is a side view of a slit lamp modified in accordance with the present invention.

Figure 3 illustrates the absorption curve of methylene blue in phosphate buffered saline to model the dye in the sclera.

Description of Preferred Embodiments

The present invention contemplates a system for non-invasively delivering laser radiated energy to the sclera of a peripheral cornea region of an eye. The laser is specifically tuned to the absorption frequency for a dye iontophoretically applied to form a fistula in the sclera and provide relief for glaucoma pressure. In particular, Figure 1 illustrates an eye 12 having a corneal region 14 and a scleral layer 16 covered by an outer layer 18, the conjuntiva. In the case of glaucoma disease, there is an increased pressure in the ocular fluid in the region 20 which can lead to loss of visual acuity if not treated. In the treatment according to the present invention, an iontophoresis probe 22 is applied to the conjunctiva 18 proximate to a region 24 of the sclera where it is desired to apply a dye that enhances light absorption at one or more selected frequencies. A current is applied through the probe 22 from a current source 26 to cause dye particles from the probe 22 to be driven into the scleral region 24. Probes of this sort are known in the art for applying various materials by iontophoresis into tissue layers. In one embodiment, the dye applied is methylene blue which has a published absorption peak for radiation in the visible at 668 nanometers. In that visible spectrum, there is minimal absorption by eye tissues or fluids without dye, so the laser beam can be focused through the cornea and so surrounding scleral tissue without dye is not ablated. Studies of the absorption spectra of methylene blue diluted in water have demonstrated a shift in the absorption spectrum to lower wavelengths. Figure 3 illustrates experimental measurement of absorption of methylene blue diluted in a phosphate buffered saline to model the dye in scleral tissue. This curve illustrates that a laser wavelength of about 590 nanometers maximizes absorption at the peak of the dimer of methylene blue diluted in the sclera.

A modified slit lamp delivery system is utilized for applying laser radiation to the region 24. In particular, the conventional slit lamp delivery system includes an optical path 30 and a microscope system 32. An operator views the region 24 along the path 30 through a goniolens 34, which has a side reflector 36. A slit beam may be projected along an axis 37 and reflected by a prism 39 to be focused on the region 24.

The goniolens is adapted to withstand the high peak powers of the laser and possesses a mirror angle appropriate for use in the method of this invention. The CGF goniolens of Lasag Corp. possesses these qualities; March et al., 18 Ophthalmic Surgery, 513, 1987. The lens is an aberration-free, entirely glass lens. One surface has a 68^* angle and is coated to provide a reflecting surface. The acrylic scleral flange of the lens helps to restrict tilting of the lens but maintains elevation of the conjunctiva when suitably positioned.

In the modification of the slit lamp system, the optical path 30 includes a dichroic turning mirror 38 which permits radiation from an optical path 40 to be introduced onto the path 30. Alternatively, the dichroic mirror may be replaced with a small turning mirror around which the physician may view along the optical path 30. Radiation applied to the optical path 40 includes radiation from a tunable dye laser 42 controlled by an operator to generate pulses by a control system 44. An output beam 46 from the tunable dye laser 42 is applied past a shutter mechanism 48 through a lens system onto a quartz optic fiber 50. The fiber conducts the radiation from the dye laser assembly, typically located at some distance, to the laser beam path 40. The diverging radiation from the fiber 50 is colli ated and focused by a lens system 52. The light is reflected by the mirror 38 through the goniolens 34 and, when reflected by the reflector 36, comes to a focus at the point 24 of the sclera where dye has been iontophoretically applied.

The slit lamp delivery system further includes an aiming laser such as a helium neon laser 54. The output beam from the aiming laser is reflected by a mirror 56 and shutter mirror 48 into the optic fiber 50 to occupy the.same path 40 as the beam 46 from the dye laser 42. In this manner, the aiming laser 54, typically a helium neon laser of relatively low power, can provide a nondamaging light beam following the same path and focusing to the same point as the radiation from the beam 46. The operator, through manipulation of the slit lamp delivery system, positioning of the eye 20, and, particularly, with fine adjustment by manual positioning of the goniolens 34, adjusts the point of aim of the low power laser beam from laser 54 to the region 24 of dyed sclera where it is desired to provide laser ablation.

While the shutter mechanism 48 is positioned to reflect the aiming beam toward the optic fiber 50, the dye laser may be fired and the beam from the laser is then reflected from the back side of the shutter 48 to a light absorbing medium 60. Within the path between the dye laser 42 and the shutter 48 there is positioned a beam splitter 62 which reflects about five percent of the laser beam through a lens 64 to a pyroelectric detector 66 which serves as an energy monitor. With this system, the dye laser can be fired as necessary to obtain the correct energy level before exposing the eye to the dye laser.

Once the aim point has been established and the proper energy level has been established, the shutter 48 is switched and the operator, through control 44, activates the dye laser 42 for pulse application of radiation. The laser 42 has a dye as the active medium to produce visible laser radiation that is absorbed preferentially by the iontophorectically applied dye at the scleral region 42. In the case of methylene blue, the dye laser dye emits in the range of 550 to 700 nanometers and preferably at about 590 nanometers. The high power beam from the dye laser 42 following along the aim path established by the low power beam from the aim laser 54, causes ablation and opening of a fistula through the sclera at region 24. That-fistula permits the over pressure ocular fluid to pass out to the conjunctiva 18 where it is disbursed gradually. The use of a dye laser having an output beam specifically tuned to the absorption wavelength for the dye enhances the preferential ablation of the dye-stained scleral tissue in the region 24 with respect to other tissue and thereby not only limits the required power application but prevents damage to tissue other than in the region where the fistula in the sclera is desired. The parameters suitable for use of the above delivery system are chosen to minimize damage that may occur to surrounding tissue and to the cornea and to maximize the chance for success of penetration of the desired tissue. Generally, the pulse width of the delivery system is chosen to have a high chance of making a crater in the sclera, but to have a low acoustic effect so that the tissue does not explode when irradiated. A pulse duration of greater than one microsecond is preferred to allow delivery of sufficient energy through a fiber and to minimize the acoustic effect which is deemed undesirable. Greater than 3 microseconds is preferred, and greater than 5 microseconds is most preferred. On the other hand, a duration of less than 30 microseconds, preferably less than 25 microseconds and most preferably less than 20 microseconds, will provide more consistent drilling through the sclera without significant thermal damage to surrounding tissue. The preferred pulse duration is about 10 microseconds.

It is important that the delivery system cause perforation and not just ablation of the sclera. Thus, the pulse energy of the delivery system is chosen to allow perforation of the sclera a large percent of the time. Again, this energy is chosen to reduce the acoustic effect of the laser light. Generally, the pulse energy is between 75 and 750 miUijoules. Energy between 75 and 250 miUijoules allows for use of a relatively low energy level with multiple laser pulses such as 10 to 15 pulses. For use of only a few pulses, a higher energy of between 150 and 500 miUijoules may be required. The spot diameter is chosen such that sufficient laser energy is provided to allow penetration of the sclera and not just ablation. A smaller spot requires a smaller fiber to avoid demagnification and a resultant larger cone angle, but a small fiber limits the amount of energy which can be delivered. As an alternative to the fiber, an articulated arm delivery system could be used. The fiber limitations would no longer be a problem, but the articulated arm is less convenient and presents other engineering problems. In any case, too large a spot size requires significantly more energy to penetrate the sclera. A high energy may also have dangerous effects within the eye. Generally, the spot diameter is between 100 and 300 microns. The cone angle, or numerical aperture, of the delivery system is chosen to concentrate the laser light on the sclera, yet to ensure that the laser energy will not damage tissues traversed by the laser light prior to reaching the sclera, or deeper tissue within the eye. The smaller cone angle increases the power density at the cornea for a given power at the sclera. The angle must not be so low that damage to the cornea results, nor so great that the target spot is shadowed in the angle. To avoid shadowing, the angle should be about 20' or less. Generally, the cone angle is best between 8^* and 15", preferably between 10' and 13^*. With a spot size of 100 to 200 microns in diameter, the distal end of the fiber should be between 100 and 200 microns in diameter to avoid the need for demagnification to the region 24. Demagnification would result in a greater cone angle which would render it difficult to illuminate the region 24 in the limbus without interference from other portions of the eye.

Given the high energy per pulse, small spot size and short pulse durations, a great deal of wear is encountered at the proximal end of the fiber 50. To minimize that wear, a tapered fiber which tapers from 600 microns to 200 microns, or 300 microns to 100 microns, has been used. In effect, the fiber provides demagnification from its proximal end without increasing the cone angle at the eye and provides for a lesser power and energy density at the proximal end of the fiber.

Figure 2 illustrates a side view of the modified slit lamp illustrated schematically in Figure 1. The Figure 2 view is from the opposite side of the system relative to the schematic of Figure 1; thus, the eye would be positioned to the left of Figure 2. As was previously noted, the conventional slit lamp includes a binocular viewing apparatus 32 by which the physician views an image in the eye. A safety shutter 67 is closed when the high power laser is energized. A slit beam is also focused at the image plane in the eye from a light source 68. The slit beam is reflected by the prism 39.

The slit lamp is modified to provide focusing of light from the tapered fiber 50 to the same point of the eye. The lens system 52 for focusing the laser beam includes a collimating lens system 70 and achromat lenses 72 for focusing the beam. Lenses of 12 centimeters focal length and 40 millimeter diameter were initially used. They have been replaced with lenses of 140-millimeter focal length and 30-millimeter diameter. The focused beam is reflected from the dichroic mirror 38 into the eye.

Between the lenses 70 and 72 is an energy monitor. The energy monitor includes a beam splitter 74 which reflects five percent of the laser light to the right of Figure 2. Reflected light is focused by a lens 76 onto a pyroelectric detector 78. This monitor provides an indication of the amount of light which actually reaches the focusing lens 72, and the difference between the energy levels determined by monitor 78 and by detector 66 indicates the condition of the optic path from the laser.

There follows an example of use of the above laser for scleral perforation. This example is not limiting to the invention. Prior to the treatment with the laser, the eye to be treated was anesthetized with topical proparicaine. After placement of a lid speculum, the site for the filtration channel was chosen by standard technique. At this site, the sclera was focally dyed at the li bus with iontophoretically applied methylene blue dye (1% solution in distilled water) for a period of five minutes, or until dye was visualized within the anterior chamber, at a current of 200 to 400 microamperes. At least a 1 millimeter diameter dyed spot is required to ensure adequate penetration when irradiated by the laser light. The patient was then seated at the laser slit lamp and positioned appropriately. In order to insure that the dye had penetrated the entire thickness of sclera, a single mirror gonioscopic lens was placed on the eye to visualize the presence of dye on the internal surface of the sclera, and to insure that the position of the dyed region was correct. The region of the dyed conjunctiva was then ballooned off the sclera with an injection of viscoelastic agent, such as Healon TM (Pharmacia) or ViscoatTM, (Cooper

Vision) using a 27-gauge needle inserted at a site adjacent to the planned filtration bleb. The above all-glass goniolens with a 68^* mirror was placed on the eye with methylcellulose and the dyed region of the sclera within the anterior chamber was visualized through the slit lamp. Sulforhodamine 640 dye, which lases at 660 nanometers was used in a flashlamp-pulsed dye laser. Using the laser aiming light, the laser was focused onto the dyed region. The light was then slightly defocused into the sclera, termed burying the beam, and the laser fired manually in single pulse mode. The ablated sclera was then visualized, and the laser light refocused into the ablation crater and the laser fired manually. This process was continued until a perforation through the sclera was visualized, or there was turbulent flow in the region of the newly created sclerostomy, indicating free flow of aqueous humor from the anterior chamber into the subconjunctival space. the goniolens was them removed from the eye and the conjunctiva inspected for bleb formation. The intraocular pressure was then measured by applanation tonometry. Subconjunctival steriod was injected at 180^* from the bleb site, and topical atropine 1% and polysporin ointment applied to the treated eye. The patient was continued on topical Prednisilone acetate 1% drops 4-6 time a day, and Atropine 1% drops twice a day.

While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. Apparatus for creating a fistula in the sclera of an eye comprising a laser for generating .pulses of laser light, each of 75 miUijoules or greater energy and of between about 1 and 30 microseconds duration, and means for noninvasively focusing light from the laser through the cornea onto the sclera to illuminate the sclera at a spot of between 100 and 300 microns diameter.

2. Apparatus as claimed in Claim 1 further comprising means for dying the sclera with a dye which enhances the optical absorption by the sclera by the laser light.

3. Apparatus as claimed in Claim 2 wherein the dye is methylene blue and the laser light has a wavelength of about 590 nanometer.

4. Apparatus as claimed in Claim 2 or 3 wherein the means for applying the dye applies the dye iontophoretically.

5. Apparatus as claimed in any preceding claim wherein the wavelength of the laser light is between 550 and 700 nanometers.

6. Apparatus as claimed in any preceding claim wherein the spot diameter is between 100 and 200 microns.

7. Apparatus as claimed in any preceding claim wherein the pulse width is less than 25 microseconds.

8. ...Apparatus as claimed in any preceding claim wherein the pulse width is less than 20 microseconds.

9. Apparatus as claimed in any preceding claim wherein the pulse width is greater than 3 microseconds.

10. Apparatus as claimed in any preceding claim wherein the pulse width is greater than 5 microseconds.

11. Apparatus as claimed in any preceding claim wherein the pulse duration is about 10 microseconds.

12. Apparatus as claimed in any preceding claim wherein the pulse energy is less than 750 miUijoules.

13. Apparatus as claimed in Claim 12 wherein the pulse energy is between 75 and 250 miUijoules and repeated pulses are applied.

14. Apparatus as claimed in Claim 12 wherein the pulse energy is between 150 and 500 miUijoules

15. Apparatus as claimed in any preceding claim wherein the cone angle of the light at the sclera is less than about 20^*.

16. .Apparatus as claimed in any preceding claim wherein the cone angle of the light at the sclera is between 8' and 15^*.

17. Apparatus as claimed in any preceding claim wherein the cone angle of the light at the sclera is between 10^* and 13^*.

18. Apparatus as claimed in any preceding claim wherein the laser light is delivered to the means for focusing through an optic fiber which is tapered from a first diameter at its proximal end which receives light from the laser to a lesser diameter at it distal end.

19. Apparatus as claimed in any preceding claim wherein the laser is a flashlamp-pulsed dye laser.

20. Apparatus as claimed in any preceding claim wherein the laser is a ruby-pulsed laser.

21. Apparatus as claimed in any preceding claim wherein the means for focusing comprises a goniolens.

22. Apparatus as claimed in any preceding claim wherein the laser and the means for focusing are coupled to a slit lamp.

23. Apparatus as claimed in any preceding claim further comprising a second low power aiming laser and means for aiming the low power laser.

24. „A system for creating a fistula in the sclera of an eye comprising: a laser; a goniolens for receiving light from the laser and directing the light to the sclera; an optic fiber for conducting light from the laser; and a lens system for imaging a distal end of the fiber through the goniolens to the sclera; the optic fiber being tapered from a first diameter at its end proximal to the laser to a smaller diameter at its distal end.

25. A system as claimed in Claim 24 wherein the laser provides pulses of between 1 and 30 microseconds at an energy level of between 75 and 750 miUijoules per pulse and the optic fiber is about 200 microns or less at the end distal from the laser.

26. A system as claimed in Claim 25 wherein the laser provides pulses between 3 and 20 microseconds at an energy level between 150 and 500 miUijoules.

27. A system as claimed in any of Claims 24-26 wherein the laser has a pulse duration of about 10 microseconds.

28. A system as claimed in any of Claims 24-27 wherein the optic fiber has a taper of a three-to-one change in diameter along its length.

29. A method of creating a fistula in the sclera of an eye comprising: providing a laser and means for focusing light from the laser through the cornea onto the sclera; generating at least one pulse of laser light of greater than 75 miUijoules each and of between 1 and 30 microseconds duration; and illuminating the sclera with the pulse of laser light at a spot of between 100 and 300 microns diameter.

30. A system as claimed in Claim 29 further comprising the step of dying the sclera with a dye which enhances the optical absorption by the sclera of said laser light.

31. The method of Claim 30 wherein said sclera is dyed with methylene blue and said laser light has a wavelength of light of about 590 nanometers.

32. The method of Claim 30 or 31 wherein said dye is applied iontophoretically.

33. The method of any of Claims 29-32 wherein the laser light has a wavelength of between 550 and 700 nanometers.

34. The method of any of Claims 29-33 wherein said spot diameter is between 100 and 200 microns.

35. The method of any of Claims 29-34 wherein said -pulse width is less than 25 microseconds.

36. The method of any of Claims 29-35 wherein said pulse width is less than 20.

37. The method of any of Claims 29-36 wherein said pulse width is greater than 3 microseconds.

38. The method of any of Claims 29-37 wherein said pulse width is greater than 5 microseconds.

39. A method as claimed in any of Claims 29-38 wherein the pulse duration is about 10 microseconds.

40. A method of any of Claims 29-39 wherein said pulse energy is less 750 miUijoules.

41. The method of any of Claims 29-40 wherein said pulse energy is between 75 and 250 miUijoules and the laser is pulsed repeatedly.

42. The method of any of Claims 29-40 wherein the pulse energy is between 150 and 500 miUijoules

43. The method of any of Claims 29-42 wherein the cone angle of the laser light at the sclera is less than about 20^*.

44. The method of Claim 43 wherein the cone angle is between 8^* and 15".

45. The method of Claim 43 wherein the cone angle is setween 10^* and 13^*.

46. A method as claimed in any of Claims 29-45 comprising repeatedly illuminating the sclera with single pulses of laser light until the sclera is perforated.

47. The method of Claim 46 wherein said sclera is illuminated with between 10 and 15 pulses.

48. A method as claimed in any of Claims 29-47 wherein the laser is delivered through an optic fiber which is tapered from a first diameter at its end proximal to the laser to a lesser diameter at its distal end.

49. The method of any of Claims 29-48 wherein said laser comprises a flashlamp-pulsed dye laser or a ruby laser.

50. A method as claimed in any of Claims 29-49 wherein the means for focusing comprises a a goniolens and is coupled to slit lamp laser system.