WO1993008677A2

WO1993008677A2 - Method of laser photoablation of lenticular tissue for the correction of vision problems

Info

Publication number: WO1993008677A2
Application number: PCT/US1992/007228
Authority: WO
Inventors: Arlene E. Gwon; Michael W. Berns
Original assignee: Allergan, Inc.
Priority date: 1991-10-30
Filing date: 1992-08-26
Publication date: 1993-05-13
Also published as: CA2122373A1; CA2122373C

Description

METHOD OF LASER PHOTOABLATION OF LENTICULAR TISSUE FOR THE CORRECTION OF VISION PROBLEMS

BACKGROUND OF THE INVENTION;

Field of the Invention:

The present invention relates generally to th field of photoablation of ocular tissue to correc vision deficiencies and treat other vision-impairin ocular problems, and, more particularly, to treatmen of the natural ocular lens.

Background Discussion:

Historically, and until only a few decades ago, eye-*glasses (i.e., spectacles) were exclusively used for most correctable vision deficiencies, including, for example, hyperopia (wherein incident parallel rays of light converge to focus behind the retina) , myopia (wherein incident parallel rays of light converge to a focus in front of the retina) , and astigmatism (a defect in vision ordinarily caused by irregularities in the cornea). However, in about the 1940s, contact lenses started being used as a viable alternative, at least for many individuals, to the use of spectacles for correcting vision deficiencies, and provided—often at a cost of some discomfort—freedom from many annoyances and appearance problems associated with the wearing of spectacles.

Another method for treating some types of problems causing vision problems was introduced by Dr. Peter Ridley just after the close of World War II. This new (although there is some evidence that it had been tried several hundred years ago) method involved t replacement of a diseased natural ocular lens, f example, a natural lens which had been clouded becau of cataract, with a plastic artificial or prosthet intraocular lenses (IOL) . Such lens extraction and I implantation is now a commonly-performed surgic procedure and is credited with saving the sight of ma individuals who were or would have become blind.

Vision correction can now be achieved on so patients, especially those with myopia, by a surgic procedure on the cornea called radial keratotomy (RK In an RK procedure, several slits, for example abo five, are made radially inwardly toward the optic axis from the peripheral edge of the cornea. The radial slits enable the cornea to flatten out a bi thereby decreasing the . curvature of the corne Candidates for RK procedures are typically near-sight individuals who cannot or who do not want to we either spectacles or contact lenses. Corneal onlays or implants, which may constructed of synthetic materials or from don corneas, are surgically attached to or implanted in patients' eyes, are also useful to enhance vision patients whose corneas have been damaged and/or scarr by corneal diseases, such as ulcers or cancer, or injury to the cornea.

Due to shortcomings associated with RK surgery an a desire to provide vision correction to man individuals without the necessity for those individual to wear spectacles or contact lenses, considerabl research and development has been directed over th past several years to apparatus and techniques fo reshaping the anterior (forward) surface of the cornea Excimer lasers—lasers operating in the ultraviole (UV) region of less than about 200 nanometer wavelength—have thus now been used to selectivel ablate regions of the cornea to resculpt the cornea o patients in a manner correcting certain visio problems. For example, regions of the cornea aroun its optical axis are photoablated to a greater dept than peripheral regions of the cornea, thereb decreasing the curvature of the cornea to correc myopia. In contrast, photoablation of the cornea i • concentrated near the periphery of the cornea t increase the curvature of the cornea and thereb correct for hyperopia. In a related manner astigmatism can be corrected by selectively varying th rate of laser photoablation of an astigmatic cornea i a manner providing an appropriate vision correction. In this regard, U.S. patent No. 4,784,135 to Blum, e al. , discloses a method for removing biological tissu by irradiation the tissue with UV radiation; while, fo example, U.S. patent Nos. 4,665,913; 4,669,466 4,718,418; 4,721,379; 4,729,372; 4,732,149; 4,770,172; 4,773,414; and 4,798,204 to L'Esperance disclos apparatus and methods for laser sculpting of cornea tissue to correct vision defects. In addition, U.S. patent No. 4,842,782 to Portney, et al. and No. 4,856,513 to Muller (as well as one or more of th above-cited L'Esperance patents) disclose masks usefu for selectively controlling the laser beam intensity o total laser beam energy to different regions to thereb enable selective corneal ablation to effect the desire vision correction. Various of the above-cited patent to L'Esperance also disclose methods for determinin the required laser ablation profile for the cornea; fo example, patent No. 4,995,913 discloses compute mapping of the cornea and computer-controlled scanni of the cornea by the laser beam.

In spite of reported short-term medical successes -both in clinical testing in the United States and i use in unregulated foreign countries— ith lase photoablation of corneal tissue to correct visio deficiencies, the verdict is still not in concernin the long-term effects and efficacy of corneal lase photoablation. In particular, questions have bee raised whether over a long term the vision correctio initially provided by photoablation of the cornea wil remain effective because of the normal regrowth of th removed epithelium layer of the cornea over the ablate area. In this regard, there seems to be. at least som natural tendency for the epithelium layer to regrow i a manner that, in time, the pre-ablation contour of th cornea may be reestablished or sufficiently so .tha vision re-correction is required. An ancillar question is, therefore, how many times and ho frequently can a laser photoablation process b repeated. Also there have been reports of haze formin on the cornea after photoablation; although thi appears to be a relatively transient phenomena—lastin only a few months and ordinarily not too bothersome t the patient—at the present there has been insufficien post-ablation time on any patients to determine lon term effects. Moreover, it appears that there may be a maximum diopter change—around five diopters—that can presently be effectively and predictably made by corneal photoablation. Still further, at least at present, the laser ablation of corneal tissue is extremely painful to the patient on which the surgical procedure is performed. Further with respect to laser photoablation of th cornea, it should be appreciated that although in s doing the cornea is sculpted in a manner correctin vision, it is frequently the case that the cornea i not itself responsible for the vision problems bein corrected. As an illustration, myopia may more likel be caused by an increase in lens size, usually as natural effect of the human ageing process, of th natural lens of the eye (located posteriorly of th cornea) . Other vision defects or deficiencies may als originate at the natural lens, while the associate cornea may itself be in a normal condition.

For these and other reasons, and for the reaso that because the lens is closer to the retina than i the cornea, less material would have to be removed fro the lens to achieve a similar vision correction, th present inventor has determined that it would often b preferable to reprofile the natural lens ove reprofiling the cornea. Such natural lens reprofilin would eliminate many of the concerns presently raise about corneal photoablation and may result in reduce risks to patients, and since the lens has no nerv supply, the procedure should result in no sensation o pain to the patient. It is, therefore, a principl objective of the present invention to provide a metho for laser ablation of selected regions of the natura lens in order to correct vision problems and to correc problems, such as incipient cataract, on the lens.

SUMMARY OF THE INVENTION:

According to the present invention, there i provided a method for the laser photoablation of ocula lens tissue, the method comprising the steps o determining the region of the lens tissue to photoablated, and directing a pulsed laser beam at su region with an amount of energy effective f photoablating the region without causing substanti damage to surrounding tissue regions. Preferably, t laser is a Nd:YLF laser having an operating frequen in the infrared spectrum and more preferably having operating frequency of about 1053 nanometers. T laser preferably has a repetition rate of between abo • 1 and about 1000 Hertz, and more preferably about 10 Hertz; and operates with a pulse width of between abo 1 femtosecond and about 1 millisecond and, mor preferably, about 60 picoseconds. Moreover, the lase preferably operates at an energy level of between abou 1 nanojoule and about 50 millijouϊes per pulse and more preferably, about 30 icrojoules. Still further the laser preferably operates with a beam spot diamete of between about 1 micron and about 100 microns and more preferably, with a beam spot diameter of about 2 microns. The laser preferably operates with a zone o effect of less than about 200 microns and, mor preferably with a zone of effect of less than about 5 microns.

In accordance with one embodiment of th invention, ^' a method is provided for the lase photoablation of ocular lens tissue for the correctio of myopia, hyperopia or presbyopia. In this case, th method comprises the steps of determining the region o the lens tissue to be photoablated, calculating th amount of lens tissue to be photoablated from th determined region; and directing the pulsed infrare laser beam at the region with an amount of energ effective for photoablating the calculated amount o lens tissue in the determined region without causin substantial damage to lens tissue surrounding suc region.

In another embodiment of the invention, a metho is provided for the laser photoablation of ocular len tissue for the removal of incipient cataract, th method comprising the steps of determining the regio of the lens tissue to be photoablated so as to remov the incipient cataract; calculating the amount of len tissue to be photoablated from the determined region s as to remove the incipient cataract; and directing th pulsed infrared laser beam at the region with an amoun of energy effective for photoablating the calculate amount of lens tissue in the determined region so as to remove the incipient cataract without causing substantial damage to lens tissue surrounding such region.

BRIEF DESCRIPTION OF THE DRAWINGS:

The present invention can be more readily understood by a consideration of the following detailed description when taken in conjunction with the accompanying drawings, in which:

FIG. l is a longitudinal cross sectional drawing of a representative eye showing, in simplified form, the cornea, iris, natural lens and retina, and showing the manner in which an image is focused on the retina in a normal eye.

FIG. 2 is an enlarged, longitudinal cross sectional drawing of a normal lens showing, in simplified form, its composition; and FIG. 3 is a simplified, longitudinal cros sectional drawing—similar to FIG. l~showing th manner in which the natural lens has regions thereof photoablated using, for example, a Nd:YLF laser operating at a frequency of about 1053 nanometers and operating at a repetition rate of about 1000 pulses per second, FIG. 3a showing the manner in which internal regions of the lens are photoablated for the purpose of correcting myopia, hyperopia or presbyopia, and FIG. 3b showing the manner in which generally surface regions of the lens are photoablated to remove incipient cataract.

In the various FIGs. identical elements and features are given the same reference number.

DETAILED DESCRIPTION OF THE INVENTION:

There is shown in FIG. 1, in greatly simplified diagrammatic form, a longitudinal cross sectional drawing of a typical, normal eye 10, which is generally symmetrical about an optical axis 12. Shown comprising eye 10, and in order from the front of the eye to the back, is a cornea 14, an iris 16, a natural lens 18 and a retina 20. In a normal eye, light from an object 22 is refracted by cornea 14 and lens 14 so as to form an image 24 on retina 20 (iris 16 being shown having an open central aperture 26 permitting light to pass through to the lens) . Shown more particularly in FIG. 2 (but still in greatly simplified form) , lens 18 is a biconvex, somewhat flexible structure which is suspended behind iris 16 and is connected to a peripheral cilary body 30 of eye 10 by zonal fibers (zonules) 32. Since lens 18 is avascular, its pathology is more simple than mos other tissues of the body; primar inflammatio processes do not occur and neoplastic growths in lens 18 are unknown. However, trauma or injury to lens 18 results in passive and degenerative changes in the lens with consequent opacification.

Focusing of lens 18, which functions to transmit and refract light to retina 20, is (assuming the lens is in its normal, youthful condition) by contraction and relaxation of zonal fibers 32. In the relaxed state of fibers 32, lens 18 assumes its maximum convex curvature and thickness; as tension in zonal fibers increases, lens 18 is stretched and its convex curvature and thickness is decreased. By this mechanism, called accommodation, the shape of lens 18 is physically varied in a manner causing images 22 to be correctly focused on retina 20 as the distance, D, between object 22 and cornea 14 changes between far and near. Lens 18 consists of about 65 percent water and about 35 percent protein (known as crystallins) , along with traces of minerals. Lens 18 is avascular, containing no blood vessels, and has no nerve supply, and comprises a thin, transparent capsule or bag 34, a subcapsular epithelium layer 36, a cortex 38 of soft fibres and a harder, dense nucleus 40 at the center. During development of lens 18, surface ectoderm invaginates to form the lens vesicle. The posterior cells of the lens vesicle then elongate to form the primary lens fibres, which obliterate the cavity of the vesicle and abut on the anterior (forward) epithelium layer 36. This process is completed early in fetal development. Subsequently, secondary lens fibres are added throughout life by the elongation and differentiation of epithelial cells circumferentiall at the equator of lens 18. The net result is th progressive internalization of previously-forme fibers. The older fibers are always found towar nucleus 40 and the younger fibers toward cortex 38.

Lens 18 continues to grow throughout a individual's life in a process similar to that in whic the epidermal tissue of the skin renews itself. However, unlike the skin where old cells ar continually cast off from the surface, older lens cells accumulate centrally and cannot be cast off. The net result is a progressive growth of lens 18 with age, associated with a decrease in elasticity and accommodative ability. The result is that the most common degenerative condition of lens 18 is presbyopia, a condition in which loss of elasticity of the lens results in the inability of eye 10 to focus sharply for near vision, such that most individuals by about the age of forty require some visual assistance, for example, that provided by spectacles, contact lenses or RK surgery.

Another common degenerative condition of lens 18 that is generally associated with aging is cataract, which is generally defined as any opacity in the lens. In the case of cataract, the extent of disability depends upon the location and severity of the opacity. Thus, a relatively small posterior (i.e., rearward) subcapsular cataract may be visually incapacitating because it is situated near the nodal point of the dioptric system, while peripheral opacities that do not impinge on optical axis 12 may cause little visual inconvenience. In general, patients initially complain of a visual disturbance, then a diminution of vision and finally a complete failure of vision. For small lens opacities and early disturbance or diminution o vision there is no proven therapeutic modality (i.e. treatment) . Ophthalmologists have long considere removal of lens 18 as the only treatment for cataract At present, the most commonly performed operation is a extracapsular cataract extraction with intraocular len implantation, the objective of the surgical procedur being to remove as much of the lens as possible wit subsequent optical device correction. The concept o selective removal of a small opacity or sections of th lens was not heretofore considered nor would it hav been technically possible.

THE PRESENT INVENTION:

The present invention relates to methods t treat presbyopia, refractive errors, and cataract b means of focusing high power pulse laser photoablatio of lens opacities and selected normal lens fibers. laser 50 (FIG. 3) which can advantageously be used fo such purpose is preferably, but is not limited to, quasi-continuous Nd:YLF picosecond laser which may b purchased as ISL Model 2001 MPL or 4001 CLS fro Intelligent Laser Systems, Inc. of San Diego, California: In general, laser 50 produces a shoc wave in the tissue at which its beam is focused, th shock wave expanding radially from the point of focu and disintegrating the target tissue (optica breakdown) , thereby causing ionization of the mediu and the formation of a plasma. This plasma is gaseous state, formed when electrons are stripped awa from their atoms in either a gas, liquid or solid. Once optical breakdown occurs, the plasma that is formed absorbs or scatters subsequent light in th laser pulse, thereby acting as an effective shie protecting underlying structures. The quicker t laser pulses, the faster and more easily the plasma created. For the present photoablation procedure, laser preferably has the following characteristics:

1. An operating frequency preferably in t visible and infrared (IR) spectrum; mo preferably, about 1053 nanometers (nm) .

2. A repetition rate preferably ranging fro about one to about 1000 Hertz; more preferably about 1000 pulses per second.

3. A pulse width preferably ranging from about femtosecond to about 1 millisecond; mor preferably, about 60 picosecond.

4. An energy level per pulse preferably rangin from about 1 nanojoule to about 50 millijoules more preferably, about 30 microjoules. 5. A focused spot size (diameter) preferabl between about 1 micron and about 100 microns; mor preferably, about 20 microns.

6. A "zone of effect" preferably limited t between about 1 and about 200 microns with littl collateral effect; more preferably, the zone o effect is limited to about 50 microns.

The procedure described hereinbelow for the lase photoablation of lens tissue ordinarily requires a initial ocular examination of the prospective patient, including refractive status, slit lamp biomicroscopy, and the measurement of axial length of lens 18 b standard applanation A-scan ultrasonography. Th accommodative amplitude of lens 18 may be measured b various techniques. For example, Adler (Moses RA "Accommodation" In: Moses RA, Hart, MA Jr. eds. Adler' Phvsioloσv of the Eve. St. Louis, Washington, D.C. Toronto: The C.V. Mosby Co., Chapter 11, 1987:291-310 which is incorporated hereinto by specific reference recommends that a convex lens be moved along th optical axis in front of the patient's eye, away fro the eye, until a target object at a convenient distanc just begins to blur—it is then assumed tha accommodation is relaxed. The convex lens is the reduced (to a concave lens), or, alternatively, th target object is brought closer to the patient's ey until the target again starts to blur. The rang between the "far" .blur and the "near" blur or maximu plus (convex lens) to blur and maximum minus (concav lens) to blur is the range of accommodation i diopters.

For the treatment of presbyopia, the amount o lens thickness to be ablated can be calculated in tw ways:

1. Based upon Normative Charts of lens thicknes and accommodative amplitude with age:

Using the ultrasound data on saggital lens lengt with age by Rafferty (Rafferty, N. S. "Len

Morphology" In: Maisel, H., ed. The Ocular Lens. Marcel Dekker, Inc. New York and Basel. 1985:1-15, 52-60—which is incorporated hereinto by specifi reference) and the accommodative amplitude at a given age, as shown, by way of example, in Duane's

Table (Borish, Irvin M. "Accommodation", Clinical Refraction. The Professional Press, Inc., Chicago, 1975, 3rd Ed., Vol. 1, p 170—which is incorporated hereinto by specific reference) , the λ k

amount of required lens tissue ablation i calculated by subtracting the desire accommodation amplitude from the patient's actua accommodation amplitude. By way of illustration 5 with no limitation being thereby intended o implied, a patient of age 60 has a lens thicknes of 4.66 mm and an accommodation amplitude of 1.2 Diopters. To increase the patient's accommodativ amplitude to that of a person of age 30 who has 10 lens thickness of 4.15 mm and an accommodativ amplitude of 7.5 Diopters, .51 mm (4.66 mm minu 4.15 mm) of lens tissue from the patient's lens This would represent an increase of approximatel 6.25 Diopters (7.5 Diopters minus 1.25 Diopters) 15 of accommodative amplitude. Since the maxima thickness change in the lens during accommodatio is about 0.5 mm, this change should be sufficien to restore the presbyopic 60 year old patient t an accommodative state. 20

2. Based on the patient's measured lens thickness and amplitude of accommodation:

The amount of lens tissue to be ablated is calculated based on the work -of Koretz and

25 Handelman (Koretz, J.F. , Handelman, G.H. , "Model of the accommodation mechanism in the human eye"

Vision Res. Vol. 22 1982:917-927—which is incorporated hereinto be specific reference) . A two micron change in lens thickness corresponds to

30 a 0.02 Diopter change in accommodation. Thus, if a patient's amplitude of accommodation measures

1.25 Diopters and it is desired to increase that to 5 Diopters (a change of 3.75 Diopters) the amount of decrease in lens thickness requir would be approximately 375 microns.

For the treatment of hyperopia, the amount of le tissue to be ablated is calculated as described abo for presbyopia. This will increase the amplitude accommodation of the patient's lens to allow t hyperope to move the focus of distant objects up to hi or her retina 20. For the treatment of myopia, the amount of le tissue to be ablated can be calculated based on th refractive status of the eye and the measured len thickness as set forth above in paragraph 2.

PROCEDURE:

For the treatment of presbyopia and hyperopia, beam 52 from a HeNe focusing laser 54 (FIG. 3a) i focused, by an associated lens or lens system 56 through cornea 14 (which is transparent to the focusin beam) and iris opening 26, to a region 56 to b photoablated by Nd:YLF laser 50 for correction of th specific vision problem under treatment. In thi regard, it is preferred that the more centrall located, older cortical and/or nuclear fibers b ablated since the width of nucleus 40 (FIG. 2) remain relatively constant with age, whereas that of cortex 3 increases. Then, a laser beam 60 from Nd:YLF laser 5 is focused by an associated focusing lens or len system 66 through cornea 14 (which is transparent t the laser beam) and iris opening 26, onto region 5 which is to be photoablated by the Nd:YLF laser beam The amount of lens tissue to be ablated (i.e. decomposed) to achieve the desired vision correctio is determined in the manner described above. Th optical zone (equatorial diameter) should b approximately equal to the diameter of nucleus 40 an the axial width (for example, about 510 microns) . Fo treatment of myopia, it is preferred that region 56 b selected so that nucleus 40 and/or centrally locate older fibers in cortex 38 are ablated using a smalle optical zone so as to decrease the curvature of a anterior (forward) surface 62 of lens 18. Such lase ablation of lens 18 to correct myopia, presbyopia an hyperopia may be termed "photorefractive phacoplasty" or "phototherapeutic phacoplasty."

For the treatment of cataracts (FIG. 3b) , beam 52 from HeNe focusing laser 54 (FIG. 3) may be directly focused by lens or. lens system 56 (with the beam passing through cornea 14 and iris opening 26) onto an area or region 64 of small lenticular opacity. Then beam 60 from Nd:YLF laser 50 is focused, by lens or lens system 62 onto area or region 64 and the laser is pulsed until the opacity is ablated (as determined, for example, by visual observation through cornea 12 and iris opening 26) .

It is preferred that if opacity area or region 64 is adjacent to lens capsule 18 (FIG. 2) , aiming beam 52 from HeNe laser 52 is focused more centrally to the opacity to account for shock wave expansion. Such treatment (i.e., photoablative removal) of incipient cataract, which is intended to delay or prevent full cataract surgery, including removal of lens 18 and the replacement thereof with an IOL, may be termed "phototherapeutic phacoablation" or "photo-therapeutic phacoectomy."

In either of the above-described treatments, application of photoablation beam 60 from Nd:YLF laser 50 produces the formation of gas bubbles at the site o optical breakdown by the focused beam within lens 1 (that is, at regions such as above-described regions 5 and 64) . The formed gas bubbles are, however, usuall reabsorbed within lens 18 within 24 to 48 hours an lens 18 remains optically clear.

Care is taken in the operation of Nd:YLF laser 5 not to rupture lens capsule 34 by expansion of lase shock wave. Moreover, if excessive bubbles are forme at the ablation site, as detected, for example, b viewing, with a slit lamp (not shown) the ablatio region through cornea 14 and iris opening 26, the lase ablation procedure is discontinued and additiona treatment is performed at a later date, for example, i one or two weeks.

By the method described above, the natural lens i an eye can be photoablated by pulsed energy from laser—preferably a Nd:YLF laser—in a manne correcting myopia, presbyopia and hyperopia and in manner removing incipient cataracts. Because th above-described laser-ablative procedures ar relatively non-invasive (as compared, for example t laser photoablation of the cornea to correct visio problems or the surgical removal of a natural lens i the case of cataract) and because lens 18 is non vascular and contains no nerve supply, no post-ablatio inflammation or wound-healing problems are anticipate and the use of steroids--commonly used after cornea laser photoablation—is not indicated. Moreover because of its structural nature, lens 18 is no expected to revert—with time—to its pre-ablativ shape—as may be the case for laser-ablated corneas.

Although there are described above methods fo laser photoablation of a natural lens for correctin vision problems for the purpose of illustrating th manner in which the present invention can be used t advantage, it is to be understood that the invention i not limited thereto. Therefore, any and al modifications and variations which may occur to thos skilled in the art are to be considered to be include within the scope and spirit of the claims appende hereto.

Claims

THE CLAIMS :What is claimed is:

Claim 1. A method for the laser photoablation o ocular lens tissue, said method comprising the step of: a. determining the region of the lens tissue t be photoablated; and b. directing a pulsed laser beam at said regio with an amount of energy effective for photoablatin said region without causing substantial damage t surrounding tissue regions.

Claim 2. The method as claimed in Claim 1 wherein said laser is a Nd:YLF laser.

Claim 3. The method as claimed in Claim 1, wherein said laser has an operating frequency in th infrared spectrum.

Claim 4. The method as claimed in Claim 3, wherein said operating frequency is about 105 nanometers.

Claim 5. The method as claimed in Claim 1, wherein said laser has a repetition rate between abou 1 and about 1000, and operates with a pulse width o between about 1 femtosecond and about 1 millisecond.

Claim 6. The method as claimed in Claim 1, wherein said laser has a repetition rate of about 100 hertz and operates at a pulse width of about 6 picoseconds.

Claim 7. The method as claimed^' in Claim wherein said laser has an energy per pulse of betwe about 1 nanojoule and about 50 millijoules.

Claim 8. The method as claimed in Claim 1 wherein said laser has an energy per pulse of about 3 microjoules.

Claim 9. The method as claimed in Claim 1 wherein said laser operates with a beam spot diamete of between about 1 micron and about 100 microns.

Claim 10. The method as claimed in Claim 1 wherein said laser operates with a beam spot diamete of about 20 microns.

Claim 11. The method as claimed in Claim 1 wherein said laser operates with a zone of effect o less than about 200 microns.

Claim 12. The method as claimed in Claim 1, wherein said laser operates with a zone of effect o less than about 50 microns.

Claim 13. A method for the laser photoablation o ocular lens tissue for the correction of myopia, hyperopia or presbyopia, said method comprising th steps of: a. determining the region of the lens tissue to be photoablated; b. calculating the amount of lens tissue to be photoablated from said determined region; and c. directing a pulsed infrared laser beam said region with an amount of energy effective f photoablating said calculated amount of lens tissue said determined region without causing substanti damage to lens tissue surrounding said region.

Claim 14. The method as claimed in Claim 1 wherein said laser is a Nd:YLF laser having operating frequency of about 1053 nanometers.

Claim 15. The method as claimed in Claim 1 wherein said laser has a repetition rate between abo 1 and about 1000, and operates with a pulse width between about 1 femtosecond and about l millisecond.

Claim 16. The method as claimed in Claim 1 wherein said laser has a repetition rate of about 10 Hertz and operates with a pulse width of about picosecond.

Claim 17. The method as claimed in Claim 1 wherein said laser has an energy per pulse of betwe about 1 nanojoule and about 50 millijoules.

Claim 18. The method as claimed in Claim 1 wherein said laser has an energy per pulse of about microjoules.

Claim 19. The method as claimed in Claim 1 wherein said laser operates with a beam spot diamet of between about 1 micron and about 20 microns and zone of effect of less than about 200 microns.

Claim 20. The method as claimed in Claim 13, wherein said laser operates with a beam spot diameter of about 20 microns and a zone of effect of less than about 50 microns.

Claim 21. A method for the laser photoablation of ocular lens tissue for the removal of incipient cataract, said method comprising the steps of: a. determining the region of the lens tissue to ^■ be photoablated so as to remove said incipient cataract; b. calculating the amount of lens tissue to be photoablated from said determined region so as to remove said incipient cataract; and c. directing a pulsed infrared laser beam at said region with an amount of energy effective for photoablating said calculated amount of lens tissue in said determined region so as to remove said incipient cataract without causing substantial damage to lens tissue surrounding said region.

Claim 22. The method as claimed in Claim 21, wherein said laser is a Nd:YLF laser having an operating frequency of about 1053 nanometers.

Claim 23. The method as claimed in Claim 21, wherein said laser has a repetition rate between about 1 and about 1000, and operates with a pulse width of between about 1 femtosecond and about 1 millisecond.

Claim 24. The method as claimed in Claim 21, wherein said laser has a repetition rate of about 1000 Hertz and operates with a pulse width of about 60 picosecond.

Claim 25. The method as claimed in Claim 21 wherein said laser has an energy per pulse of betwee about 1 nanojoule and about 50 millijoules.

Claim 26. The method as claimed in Claim 21 wherein said laser has an energy per pulse of about 3 microjoules.

Claim 27. The method as claimed in Claim 21 wherein said laser operates with a beam spot diamete of between about 1 micron and about 20 microns and zone of effect of less than about 200 microns.

Claim 28. The method as claimed in Claim 21 wherein said laser operates with a beam spot diamete of about 20 microns and a zone of effect of less tha about 50 microns.