AU603667B2 - Surface and geometric modification of optics made of crosslinked polymers by ablative photochemical decomposition - Google Patents

Abstract

An optical element made from crosslinked polymers is worked by ablative photochemical decomposition. To this end, the crosslinked polymer is exposed to controlled, coherent irradiation whose photon energy is significantly higher than the dissociation energy of the covalent bonds in the polymer and whose fluency is sufficient to remove the resultant decomposition products.

Description

60367 Form COMNION'WEALTH OF AUSTRALIA PATENTS ACT 1952-69 COMPLETE SPECIFICATION

(ORIGINAL)

Class I t. Class Lod~god.

Publisiied: II.! ~P Nq1If'c Art: Nanio of Appicant: Cf BA-GCEITGY AG Nldnns of Appliant, Klyb. ckstrasse 141, 4002 Basle, Switzerland JACK CARSON WHITE, MANFRED ACHATZ and [ULRICH MULLER "zEDWD. WATERS-& SONs, QUE4 STREET, MEJCU~,AISTRAIAF SIJRFACEAND GEOMETRIC MODIFICATION OF OP'TICS MADE OF C'dOSSLINKED POLYMIERS 11) A11lLAT IyE PHOTOCIEM I CAL DECOM1POSI TION Tt~pt"

LI

1 Background of the Invention The concept of modification of optics or optical surfaces is well known within the industrial sector. The most well known prior art consists of surface and geometric modification through mechanical means such as lathing, scribing, and contact polishing. These processes induce material removal through mechanical shear stresses imparted at the point (or points) of contact. Other prior art .0 employs the use of a carbon dioxide laser for modification of lenses. These modifications include small holes made in contact lenses, marking identification indicia on lenses, as O 0 a well as modification of optics and optical surfaces on thermoplastic polymer lenses. In this process reasonable i0 surface and geometric modification may be induced by localized heating of the thermoplastic surface. This 0, localized heating in turn induces melting and subsequent flow of the thermoplastic due to surface tension and reduced viscosity of the melted polymer. Although this CO 2 laser technique has many advantages over mechanical processing, this process is not suitable for all polymeric optics. For example, crosslinked polymers ,uch as PHEMA, CR-39, and siliione, do not melt and flow when subjected to heat.

Instead, a rough and translucent surface is produced due to the chemical bonding within the crosslinked polymers. The present invention relates to a lens made of crosslinked polymers which is modified by means of ablative photochemical decomposition. In this manner, undesired polymeric material is removed from the surface of said lens through the use of a controlled beam of coherent radiation having a photon energy substantially greater than the dissociation energy-of chemical bonds in the polymer.

S2 As stated, the geometrical modification of optics by mechanical means, as well as carbon dioxide lasers, is well known. For example, U.S. Patent No. 4,194,814, issued on March 28, 1980, discloses ophthalmic lenses having an engraved surface indicia. In this patent, the use of a carbon dioxide laser, emitting in the infrared region, to sublimate or vaporize contact lens polymeric material to form a predetermined depression of identifying indicia is described. The indicia is characterized in this patent as o°0 "well-defined craters or sets of grooves", the sides and bottom of such indicia being "typically frosted, or at least translucent", as seen in U.S. Patent No. 4,914,814, column 0 0 5, lines 26-37. This substantial translucency is asserted Sas an advantage, as seen in column 6, lines 35-38.

o 0 0 Carbon dioxide lasers, emitting frequencies in the o o infrared region characterisiticlly have a photon energy of about 0.12 eV., far less than the dissociation energy of the S°o typical covalent bond present in the polymer networks. For example, carbon-carbon covalent bonds have a bond energy of about 3.6 eV., carbon-silicone bonds about 3.2 eV., carbon-nitrogen bonds about 3.2 eV., carbon-oxygen bonds about 3.7 eV. and silicon-oxygen bonds, about 4.8 eV. When lenses mad~ of polymers are subjected to laser frequencies corresponding to less than the bond strengths, one photon is incapable of directly forcing bond scission. Rather, the photons are absorbed into the vibrational modes of the molecule, i.e. the energy is deposited as heat. Eventually one bond may absorb a sufficient number of photons to initiate dissociation. However, during the time the bond is accumulating sufficient energy to be able to dissociate, other parts of the molecule are absorbing energy by vibrational energy transfer, resulting in localized melting -3or polymer network collapse. Upon bond scission, the ablation occurs as a result of heat induced sublimation or vaporization, leaving a frosted or translucent depression in the lens material. These surface defectz are most noticeable in crosslinked polymers where the melt flow is restricted.

Other prior art includes U.S. Patent No. 4,307,046, issued December 22, 1981, which recited the cutting and 0 polishing of a contact lens material formed from an 0 unspecified polymer using a sharply focused carbon dioxide laser beam. No specific example is given.

o 0 o o Carbon dioxide lasers emit energy in the long 0o0a wavelength 9-11 urn.), far-infrared spectral region.

In the mid to late 1970's excimer lasers, high pressure gas 0 0 lasers, wer developed. Excimer lasers emit in the short 0 00 wavelength ultra-violet spectral aregion, with wavelengths varying from about 150-350 nanometers, corresponding to photon energies between about 3.3 and 6.4 eV., (as determined by Planck's law), depending upon the excimer lasing medium. While the carbon dioxide molecule was the typical lasing medium in the early gas lasevs, the excimer laser's electronically excited level is a diatomic molecule made up of a rare ga atom and a halogen atom, such as ArF, KrF, XeCl and XeF. These molecules, which exist only in excited states for a few nanoseconds, are called excimers or exciplexes. Excimer lasers find typical application in dye laier pumping, photochemistry and more recently in semiconductor processing, chemical vapor deposition and photol ithography.

4 The use of eximer lasers to remove material, or etch, material from an uncrosslinked organic polymer films having carbon-carbon bonds in the backbone thereof, such as films of poly(methyl methacrylate), poly(ethyleneterephthalate) and K.apton® polyimide, by ablative photochemical decomposition have been recently described. See, for example, Dyer et al., J. Appl. Phys., Vol. 57, pp. 1420-1422 (1985); Srinivasan et al., Polymers, Vol. 26, pp. 1297-1300 (1985); and Garrison et al., J. Appl. Phys., Vol. 57, 2 o" pp.2909 et seq. (1985).

ooo 0 Surprisingly and unexpectedly however, it has now 0 0 been found that lenses, especially contact lenses, and precursors thereof, such as contact lens buttons and ooo"0 xerogels, all of crosslinked polymers, can be geometrically modified by ablative photochemical decomposition to form o optically clear contact lens materials, by subjecting said lenses or lens precursors to a controlled beam of coherent 0* radiation having a photon energy in excess of the dissociation energy of the polymer, provided said beam possesses a fluence, or photon density, sufficient to ablate the dissociation prodcts in the substantial absence of thermal iistortion.

Accordingly, one object of the invention is to provide a contact lens which has been geometrically modified by ablative photochemical decomposition of crosslinked polymer material in a controlled predetermined manner.

It is another object of the invention to provide a method for geometrically modifying a polymer material in a predetermined manner to 9orm a contact lens by ablative photochemical decomposition by subjecting said polymer to a controlled beam of coherent radiation havinq a photon energy substantially in excess of the bond dissociation energy of the polymer, and a fluence sufficient to ablate the dissociation products in the substantial absence of thermal distortion of the lens material.

These and other objects of the present invention are apparent from the following specific disclosures.

a Detailed Description of the Invention.

One embodiment of the present invention relates to a lens formed of a crosslinked polymer having a backbone 0 contain ing covalent bonds, wherein said lens is 000geometrically modified by material removal from the surface thereof in a predetermined manner by ablative photochemical 0000decomposition by subjecting said lens to a controlled beam of coherent radiation having a photon energy substantially 4,00in excess of the energy of dissociation of said covalent bonds, and having a fluence sufficient to ablate t-he resulting dissociation products in the substantial absence of thermal distortion of said polymer.

The resulting geometrically modified lens material is characterized by the substantial lack of translucent grooves or cratering associated with conventional thermal laser ablation. in other words, the ablated surface is typically smooth and optically clear.

Preferably the lena material is a contact lons.

The problems associated with thermal ablation of crosslinked polymeurs suitable for use in lenses, eopecially -t -1IC contact lenses, are generically more extreme than those associated with non-crosslinked polymers. A cross-linked polymer is essentially a three-dimensional network. As a result, crosslinked polymers are not thermoplastic and cannot be ablated by simple thermal exitation of the polymer to yield a smooth and optically clear surface. In attempting to ablate a typical crosslinked polymer by employing photon energies less than the dissociation energy of the covalent bonds holding the polymer network together, cratering, polymer network collapse resulting in visual translucency, pitting r cratering, and, under extreme conditions, charring may occur as the photons are absorbed until the vibrational energy accumulated finally breaks down the polymer, inducing sublimation or vaporization. A S non-crosslinked polymer, being made up of simple strands of polymeric materials, is generally thermoplastic, and material can therefor be more easily thermally ablated from the surface thereof.

Due to the nature of the photochemical decomposition induced by coherent radiation having a photon energy substantially in excess of the covalent bonds of the crosslinked polymer, the nature of the crosslinked polymer is not critical. For use in contact lenses, the crosslinked polymer is one which is biologically and optically compatible with the ocular environment.

Suitable crosslinked polymers include those croslinked polymers known to be useful in the manufacture of lenses and are widely commercially available or described in the literature. Useful crosslinked polymers suitable for use in the present invention, for example include those having covalent carbon-carbon, carbon-nitrogen, -7 000 0 000000 0 0 0 00 0 0 0000 000000 C 0 00 0 0 00 0 00 carbon-oxygen, silicon-carbon and/or silicon oxygen covalent backbone bonds, and possessing a bond strength, depending on the backbone constituents, between about 3 and about 5 eV.

Where the cr!,osslinked polymer employed contains primarily carbon-carbon and carbon-oxygen bonds, a photon energy in excess of about 3.6 eV. is generally suitable for bond scission in the substantial absence of thermal ablation.

Where the crosslinked polymer contains a substantial number of 3ilicon-oxygen bonds, a higher energy, for example in excess of about 4.8 eV. should be employed. Preferably the photon energy employed is greater than the bond energy of any covalent bond present in the polymer backbone, in order to minimize photon absorption as heat, as well as quantum yield losses.

The nature of geometrical modification can vary widely, and inclvdes, without limitation, l11ens pol.ishing, e.g. of partially machined or molded lenses, the generation of mono- or multi-focal zones on the front or rear surface of the lens, the removing oaf flashing from the edges of lenses, such as molded lenses, 'Llie craation of a comfort ch..

0 mfer on the lens periphery, the engraving of indicia on the lens sur'face, and the like.

Preferred coheretit radiation can be most conveniently obtained by using an exirner pulse laser to generate the beam. Howevc-r, a fluorine gas lasing system can also be employed. Preferably the coherent radiation has a photon energy between about 4eV and about 8eV, most preferably between about 4eV and about 6.5eV. One drawback associated with the use of fluorine gas lasers, e.g. having a frequency of about 15" umn and a corresponding photon energy of about 8coV, is that the beam may interact with atmospheric oxygen L 8 and nitrogen, requiring a vacuum, etc. for optimum performance characteristics. This inconvenience can be avoided by employing an eximer laser or the like, to generate a coherent beam of radiation in the range of between about 4 to about 6.5eV. For convenience and general availability, KrF eximer gas lasers, having a lasing wave length of about 248 nm corresponding to a photon energy of about 4eV, and especially ArF eximer gas lasers, having a lasing wave length of about 193 nm corresponding to a photon energy of about 6.3eV, are most preferred.

.0°0 The lower limit of the fluence of the coherent S' radiation at the polymer surface useful in ablating polymer material will, in part, be dependent on the nature of the polymer. In general, the minimal beam fluence as measured "°oo at the surface of the polymer material to be ablated, is 0between about 5 and about 50 mJ/cm 2 Also, at very high fluences thermal related ablative effects may occur and o 0. accordingly are generally to be avoided. In general, S however, beam fluences up to at least 500 mJ/cm 2 can be employed without significant thermal related ablation effects, such as translucent irregularities, impairing the desired geometrical modification.

The depth of ablative removal of polymer material will be directly proportional to the length of the beam pulse duration at a given fluence and the nature of the polymer material. Generally, the pulse duration for ultraviolet emitting gas lasers is between about 5 and about nanoseconds.

If desired, the duration of the normal inherent pulse duration of con aerically available ultraviolet lasors, e.g.

eximer or P2 lasers, can be shortened as desired through the 9use of a conventional rap~idly rotating mirror/slit assembly interposed between the laser beam and the lons polymer.

Conveniently, the area of material ablated from the polymer surface of the lens material is controlled, for example, through the use of appropriate -masking techniques.

The ophthalmic lens material to be geometrically modified may be in the form of a xerogel contact lens :replica of a hydrogel contact lens, a hydrated hydrogel contact lens or a hard contact lens. The lens material may be a molded, machined or a partially molded or machined ""'contact lens or lens replica and may be in partial or fully 2polished form depending upon the geometrical modification to ~:eperformed on the lens material. Where a ),erogel is employed, it is hydrated afteir ablation Zor placement in the eye.

As the ablative photochemical decomposition is performed using a preselected controlled beami of coherent radiation having a photon energy substantially in excoos of the energy of dissociation of polymer backbone covalent bonds, the nature of the polymeor can vary widely.

Preferably, the final, lons product in, suitable for placonwent in direct contacL with the human eye. 2%s the artisan can nppreciate, it is ossonti al that upon photochemical scsoaion Such bonds, 0h0 reOsulting dissociation productsar ablated cleanly, in the substantial absence of an charring or debris f-ormation at the lons site whicla hasj bcon jo~odto outch geomtrical tnodifioation.

SUitable Contact, IQnsl MateriaLo o iein na o WL'th tho instant invention include ho'~ra wide varity 2 Polymers suitable for fabricating contact lcowsoo and useful in the practice of the present invention inclule conventional contact lens hydrogel materials such as those of polymers of hydroxy substituted lower alkyl. acrylates or mothacrylates or the like, crosslinked with a crosslinking agent, such as ethylene glycol dimethacrylate or divinyl benzene as in U.S. Patent Nos. 2,976,575 and 3,220,960 to Otto Wichterle et or copolymers of hydroxyl substituted lower alkyl. acrylates or methacrylates and N-vinyl pyrrolidone and a crosslinking agent, such as ethylene glycol. dimethacrylate or divinyl benzene as in U.S. Patent Nos. 4,123,408; 3,639,524 and 3,700,761; and bydrogels ~'~containing acrylic or methacrylic siloxanes, such aG those containing a mathacryJloyloxyalkyl polysiloxane, hydro~tye thyl niethacrylate and ecy-N-vinylpyrrolidone as in U.S, Fatolt No. 40246,389.

Suitable hard contact lons im&atriaYs iw.,luice crosslinked polymers cf fuorincitod alkyl athui.' poly~mwvs as in U.S. Patent No. q,440,910 to nice et al., a bis0mothacrylate containing siio,%ano dio3. copolyniiri.-od u one on more al~kyl mthacrylatos, mothacrylic ncid -and L crosslinking agent, such asv ot2ylono glycol iohcyY2e i~~n U.S. Patent 4,486,577 to Rullor ot al; or copoi'yt;)r o0 a mixturo, of tmono- and Abis-acryloxyalkyl o '2:.u with alk;y] rnthacrylatoro, Mnthacrylic acid1, an a(Iryloxyalkylsilanol and a croslinking agent -,uQ14 1-is e hhylelnoglyciol haayUt 7Ln Patont ~i ~-p~moblecrosslinkod ontact lons mate,-alci az, oE.a"'nl? n Eo.tact Lens Pra 2V% 0, er C i 1 1Y available suitable soft hydrogol 1lon s m:1 tre:r, i ~O isciosad, for ex'ample, in Soft Contact Lenses: Clinie..l a n 0 Aooliod Technology, by aca gbn, 2.9 at .'2wough thoe uooe Qf cli table,, nnl--in'j tuctmejtv. -Le 2.un, material may ho geometrically modified in a o) ways. For examnple, the instant method can bo usod to Qcflorate either a monofocal zone or multifocal zon~s ns ablative romoval of mnaterial from the loris surfa.co, Lto surface poliih the Iens iuatorialf or to ongrave identification mar'Rings onl the Ilonas urface or to eic ocdge flaohinq or to provide a comfort chamfcr cat the, uts edge. 4'W the inotatnt mfethod provides for ab!Latiori o7 polymeor material in the rsuLbotanrial a bsenco of therw 2.

diotortion, and th(e amount of matorial romovod cazn prudotormiAnc with In OxtreMOl2,, high doqreeoo 0 cc 1-j ZL.- la4,g' L~ 2. I;U ~tl~ ut t~.Ec onoo, for e:a~ebifocal zone-s, on contachw.

iaterials dlue to th() intiorent photo-chlmical doc omp os 1'ti 11 d tIc d. Mato:ial reriova1. may be prodotorminnd in the f.h tngot~romreg~oion of depth, while scanning electron crs- Tllusitratoc that a clean undisturbed Osureac, remains. 13lasaing the corent radiation throuqh a shaped mask, nn' 4,maging that shaped aperture onto the,, contact I.ona ui~v with a fosinq Iona, such as a quazrt- foquoin J!en,&, iblativc photo-decompoition, will occuzr in that C-ocusow! 1hapod area on the lena surface. The shape of the nask, iperture and resultant focused aroa cans vary widoly, howofv'! I Citrcular aporfur0 Iq 1-VpiCc~lle 11esirabl, Whorc' -itn.

-1 II :erydon! Ly wi thin thue Caoront~Lr:i tcterial will bfe uniformly ablated from the ln Ic'.

2he geometry, or curvature of a lons may be mrodl.

example, by moving the imaging mask,, the f-ocusing leci I: the object contact lens during procossing. Duo LQ t lie th-,It hh") i-l'i'lo, ni 3zo governed byh e l r: I diotance from focusing objective t I. 1otal distance of objctive, and w4a magnificaion, io~vinj any one, or a combination of tho iriaging i..

eocuslng lons or the object contact lens material, will.

change the size of the area to he processed. Por oxam:'. pl, usifg a circular maok, placing tho object lona front cUr> porpondlculac to the bean, and beginning with a vory csm...1 imao sizo and slowly incraaing that image, the c,,,ntral 'uiea of the lens front ourfac will have more material eomovodi than the poriphery' thereby creating a tlatteni:,: tho radius in that zonoi This may, Of course bQ donce oai e.ither the front or~ rear surface oO. the contact lonco. !P4 .v.ltpulation of, !.he pulse,, ropotition rate, powar por pui.; ind the rate at which tho imatg size changsoo the lpprepLiato power may bQ achieved. Thst analOgoustrly, O.1 .,iay ltaso the power OC a Ions by removing more mtrV2rr~ Oromrt tho periphery than from the central optical portion the lens. Likewisot through the use o suitable ~n;akin j techfitiuos, optic~il 24 oaq on eny isn 1 cn.,44 uitny d'mv :mn~z 13- If desired, the instant methjod m-,ay also be used tu polish contact lenses. Surface polishing is often required, for example, on lathed hard contact lens materials and lathed xerogel lens replicas of hydrogel lenses. The ex<iier laser has been found to be surprisingly effective in the smoothing of the surfaces of such lenses as the ablation effect tends to be greater at the microscopic peak-s of the irregular surface of the lathed lens material. Scanning electron micrography studies show that an optically smooth surface is obtained, in some cases superior to that of standard polishing tachniques. In this process, the eximer laser radiatiork is imaged onto the front or rear surface of: -the leris, with the treated surface maintained perpendicular to the ioeam of coherent radiation, engulfing the entire surface of the object contact lens, while the lens is rotated eliminate o~foctn of possible incongruities within the beam.

The standa~d practice for engraving indiciz on lensoesuch as hard lenfwes and xerogelsc consists of using a diamond tooled mechanioel engraver. By use of an excimer laser a superior of-,ravi.ng of indicia, wherein the walls and floor of tbo indicia are optically smooth and substantially devoid of tho frosted or pitted characteristics associated with the use of carbon dioxide laser, can be obtained. In this proceduret the radiatic .is izuaged onto the lens surface, Using an appropriate maisk containing the desired information, such as the base curve, power, company name or I go or the like, to be placed on the lens surf ace These charaters ore placed in the standard location on the lw near the periphery, away from the optical zone. The images caused by photochemical oblation of the surface in the image of tho desired characters are crisp and clearly visihlo, i 14 Sthe actual surfaco theroof zemains optically transparent. The clarity of the image is actually induced by the highly resolved image edges, where light is refracted, not ncattered.

Vor fully molded and scomi-molded lenses, edge "flashing" nay occur during the molding process. This flashing must be removed in order to maintain comfort for the lons wearer.

The tse of an oximer laoser is also very wEll suited for removal of such flashing as it is able to remove these small bits of material cleanly and concisely. The removal may be accomplished by passing the coherent beam through an annular mask, supported on a quartz or other liV transparent support and image the ring of coherent energy onto tho lons edges, with the front or back surface of the lens porpendicular to the beam. Alternatively, one imay 2employ a partial mask and rotate the contact lons matrial. Thu oextraneous material may thereby be removed, leaving a coooh continuous edge. Similarly, this technique may similarly La employed to place a comfort chamRFor on the pericphr, Co a contact lens, such as a lathed contact lon.

In the following Ex ampls e an ::iire i: lasc:1 3. a0 o 200, manufactured by Landa Physik, was employed. ArF 9 used as the lasing medium. The operating frequencies can !a vatried from 1 to 10 Hz with a power of approximately 15C toa 200 millioules per pulse, and a .2anin- transinion about 193 nm wavelength.

The following Examples aro 4cr illuotrative purp jnly and are not to he construed as linitinq the mauea ni bounds of the present invention.

Example 1 The eximer laser was filled ith ArF and operated at a repetition rate of 1 Hz. The total output was measured at 100 milijoule per pulse for the entire beam. A 5 mm circular aperture mask was used to create the central zone an the lens, reducing the energy output throijoh the mask to millijoules pet, pulse. This 5 mm aperture was then imaged down to 0.5 mm on the lens surface, using a 100 mm focal length lens of ultraviolet grade fused silica optimized for transmission at 193 rimn wavelength, with the initi-2. distance from the mask to the focusing objective being 110 cmn and the distance from the focusing objective to the image plane being 1.1 cm. A precut xerogel lens of hydroxyothyl tnethacrylate crosslinked with ethyleneglycol dimethacrylate was then positioned in the focal plane with its optical axis concurrent with that of the laser and the go'iusin- such that the beam is substantially perpendicular to the lens front surface. The contact lens to then stopped back away from the focusing objective in 1 t,:m stops, eachi time pulsing the laser once. This was Lrepeated through 50 one mnil~imeoter steps, for a total og 51 Vulo and a maximum~ processing zone f 3 mmn dianieter. Due to the defocuning nature of translating away from the Creel Llano, no significant step ringr, were detected in the final Lons and a ohnein tho contral zono lens geotmtry was TheiierlcCr wao fille'd Withl ArV' a4 tile locing Lm~.rlat 193 nz, Wavlength. The power wao. measured iavJ Otorlminu e about 150, pil~ul~ur TZhe' srew w- 16 rectangular beam was then masked at its periphery in order to reduce beam edge profile effects, thus reducing the energy to about 115 millijoules per pulse. This beam was then imaged onto a xerogel lens of hydroxyethyl methacrylate crosslinked with ethyleneglycol dimethacrylate, having a lathed but unpolished surface, with a magnification of one.

the lens was slowly rotated at 60 revolutions per minute while the laser was pulsed at 10 Hz for a total of ten seconds and one hundred pulses. Scanning electron microscope evaluation indicated a smooth surface wiun lathe rings and surface imperfections greatly reduced, illustrating superior surface qualities in comparison with S° conventionally polished xerogel lenses.

Example 3 SThe eximer laser was filled with ArF and the output measured -L 200 millijoules per pulse. A mask with the transparent logo CIBA having a character height on tho mask 0 o o f 3 mm, to be reduced to 0.6 mm on the lens surface, was employed. This mask was placed betwoon the beam and a focusing UV grade fused silica lens, having a 250 mm focal length, with the mask 150 cm from the focusing objective and the target lens 30 cm from the objective. The lcasr war pulsed at 4 Hz for optimizing evaluation, with the xorogol lens replica being fabricated from hydro::yothyl mothacryl eo polymer crosslinked with othylonoglycol dimethacrylate.

Cptimum results were achieved at 20 pulses yielding a 0.i39 rn character penetration into the lens surface. Scanning electron micrography revealed an optically clear smoothi ourfaco had boon gonorati,-, with hrDp init~ in the fou r of the indichia.

Claims (4)

1. A method of geometrically modifying the surface of a lens or semif inished lens or a lens mold part or lens replio-i xerogel formed of acrosslinked polymer having a back- bone containing covalent bonds comprising the geometrical modification of said lens or semifinished lens or lens mold part or lens replica xerogel by material removal from the surface thereof in a predetermined manner by ablative photo- chemical decomposition by suibjecting said lens to a control- led bean~ of coherent radiation having a photon energy substan- O tially in excess of the energy of dissociation of said cova- lent bonds, and having a fluence suffi1cient to ablate the 0 resulting dissociation products from the lens surzface in the 'o~o 0 substantial absence of thermal distortion of said lens ~000; material, Such that the ablated surface is substantially smooth and optically clear.

2. A method according to ,.iaim 1, wherein the coherent. radiation has a photon energy between about 1eV and Salbout 12feV, more sp<ecifically be-tween about 3eV and about 8eV.

3. A mothod accorzding to claimh 1, wherain the beara ~lunceof, the coherent radiation is between abou~t 5 and about 500 millijoule per square t,-entizaeter of lons c~urface to tt. ablatively rormoved.

62. 2% r.,._thcd accor(incr to claisn L, w.huin the~ Lons 4. -la ontact lens or contact lunn roplica erogcA A etc accordivq to vli;4., w' u="ain ttbo Lono a Lour"~c 2Ll lic-l~ OA w 1s 6. A method according to claim 5, wherein the lens material is a hard contact lens. 7. A method according to claim 1, wherein the lens material is a hydrated hydrogel contact lens. 0. A method according to claim 1, wherein the geometrical modification is the placement of indicia on the lens Surface by the photochemical ablation of material from said Surface to a predetermined depth corresponding to said indicia 9. A method~ according to claim 1, wherein the geometrical modification is employed to generate a monofocal or rultifocal zone on the surface of the lens. A method according to claim 1, wherein the georautrical modification is employed to polish one or more surfaces of the lens. 1.A wethod according to claim I# wherein the energy fliuncu of the coherent radiation is between about 5 milli- j(ules, and about 5 joules per square centimeter of lens -,iir- fLucu to be ablativJly removed, more specifically between LIoout 20 millijoules and about 2 joules per square centitetrL c~lons suraco to be ablatively removed, more specificallyX. 2tenabout 50 millijoules andW about 500 millijoules 1?Cr ozS ijrgacr f '~a)a~vlrr)' -19- 12. A method according to claim 1, wherein the modification may be achieved with a single laser pulse, or multiple pulses. 13. A method according to claim 12, wherein the modification may be achieved by pulsing the laser wherein the frequency of said pulses may vary between 0.01 Hz and M4Hz, more specifically between 1.0 Hz and 500 Hz. 14. A method according to claim 1, wherein the lens material may be lenses or semifinished lenses for optical instrumentation, including, but not limited to, camera lenses, microscope lenses, projector lenses, laser lenses, and telescope lenses. A method according to claim 1, wherein the lens material may be~ lenses or semifinished lenses for spectacle 16. A method according to claim 1, wherein the ,,,t-ril uy be a lens mold part or o I,.finihed lens mold I? A method accordIng to claimn 1, wherein the lens ~~terisi contact lens, or a ounifinished contact lens, oza CK ,-tact luns raold part. A thcal cccrdincj to claim 1, wherein the lens i~ ~a :~h~'ratd hyr~7u (hdr~rhilC)ontact lens. 20 19. A method according to claim 1, wherein the lens material is a nonhydrated hard, semirigid, or gas permeable finished or semifinished contact lens. A method according to claim 1, wherein the lens material is a hydrated hard, semirigid, or gas per~meable finished or zemnifinished con-F-act lens. 41. A method according to claim 1, wherein the lens material is a nonhydrated hydrogel (hydrophilic) intr- ocular ophthalmic lens. 22. A method according to claim 1, wherein the lens material is a hydrated hydrogel (hydrophilic) intraocular ophthalmic s. 23. A method according to claim 1, wherein the lens xaturial is a nonhvdrated hard, semirigid, or gas permeable f inished or emifinished intraocular ophthalmic lens. 24. A method according to claim 11 wherein the lens maturial is a hydrated hard, semirigid, or gas permeable finis;1iod or numifinished intraocuilar ophithalmic lens. A method according to claim It wherein the 9~.~~trialmodification is the placement of patterns on the leii.- surtace by the, photochemical ablation of material from zoai 2 uurfaco to a predotermined depth corresponding to said ~L~rnsto ixrucu Lear eitcha.-jo. or desiired mowvunt of the C' 21 26. A method according to claim 26, wherein the pattern created by the geometrical modification itself may induce a monofocal or multifocal zone on the surface of a lens. 27. A method according to claim 1, wherein the geometrical modification is employed in creating or finishing an edge profile which is optically smooth in order to minimize diffraction and/or ocular irritation in the case of ophthalmic lenses. 28. A Pethod of geometrically modifying the surface of a lens or ophthalmic lens substantially as herein Cescribed with reference to any one of the Examples. 29. A geometrically modified lens or ophthalmic lens when produced by the method of any one of claims 1 to 28. DATED this 20th day of August, 1990. hv 33 ffl1t:nt Ao cryG tf::jt?~c8~nliO.W"f I' L