GB2228099A - Surgical laser having an annular beam - Google Patents

Description

k i -I- SURGICAL LAS?RS v v The ir.ve,.-tion relates to medicine, i.e., to

opthalr-DIDgy and is concerned more s--tecifically;,,i th dev ices for surgical treatment of ametropia (that is, MYDpia and htipermet2Dpia).

one -.rior-grt device for surgical treatment of ametropla is known to CDMpriS6 a UV pulsed laser and a distributor of laser radiation enexgy, density over the laser beam cross-sectional area, said distributor being placed across the path of the laser beam 'lReLo.,t of the 'Centre Scientifique IBMI, Paris, Prance, Document No. F10,4$ 1986. K.F.anna et al., 1Excimer Laser Refractive Keratoplasty').

In the device mentioned GbIDve the distributor of laser radiation energy density is in fact a rotary disk provided witb a slit having a preestimated shape.

It is due to the effect of many laser pulses with a preset ratio between the repetition frequency oil radiation pulses and the slitted disk ro4UatiD,-, 'Lre,-ue-.cy that the shape of the corneal surface is chanied in order to correct ametrDpia.

However, only part of the cornea is ex-osed to momentary irradiation, said part depending on the of the slit and on its angular position at a jiven instant Df time, which impedes the obtaining of smooth surfaces of a preset profile, since each radiation pulse removes a layer from the Cornea having vertical walls, ttle shape of said layer following -that of the slit. Hence the 9 required shape Of the corneal surface is approximated by a stepped surface SO that many shallow-deoth layers are to be removed in order to Obtain a s.-ooth surface. This extends the Operating ti:,,ie, i.e. hampers the conduction of an operative procedure, since it requires precise fixation of the patient's eyeball with respect to the laser bearn for a prolonged period Of time. Besides, the C) laser radiation energy is utilized but inefficiently, which also prolongs the operating, time. The device is io too complicated in manufacture, since precision accuracy in making the slit the latter involves and a machanis.m 1Or its rotation, accurate:neasurement of the slit anga iDsition and time correlation between the 00SitiDr. Of said slit and 'v-he instant of laser pulse emission.

1 ar Another state-Df-tL-16-P,.rt device for surgical treatment of ametropia, in particular, myopia is described in 1.Ar Journ. of Ophthalmolog.7i'g v. 103, i.139 pert II, nald et al., 'Refractive Surgery with the Excimer Laser' p.469, 1987.

In the device mentioned above the distributor D--P the density of laser radiation energy is made as a diaphragra placed across the Dath of the laser beam, the dia::.eter of said diaphragm chanc.ing stepwise from Dulse to pulse according to a computer program in such a manner that the shape of the corneal surface is chanj.ed for a required correction of myopia.

t,,ie use o-O sai-1 device, 3.s as if e device de-s.cribed above, only pert of the cor,--.ea is ex,:c)sei -uD nomentary irradiation, said Dart 1, n,:z 1. ng on the dia. hra,r, diameter a iven instanz of timel which impedes the obtaining of a s-,ootuh corneal sur'i-ace; bes.-Ldes, ruany shallow-de tn layers are to be remove ror- U-n 3 C Surf 3ce,,tich exte nJs o p er a -15 i n- ti-e, since iu re,aires Greci.-se fixe-cion of t, e a 'i -- r, z 1 s b P- 11 r e s D e t t D t b e 1 a s c be an, f o x U j a lroli)ried pe2iod of time. In Pdd.i-tion, the 1 a s er ener--., is utilized inefficiently, also rD!Dns +..he And Dne more Gf si- eti-opis 123 device for sur-rical -ureal is kncv,,.,i -UD comprise a U7ulsed la ser e.n,- a d istribat-or of la ser radiat ion over the laser beam C-rDSS-SeCt-iOnal are52 said dist-ributor beinj. placed across -whe of 1-.se.r beam (PC'-7,/SU 88/00280).

In the device -,,e-ntiDr.ed above thd of laser ra,Aiation en.-r,--,,y de,-.siuy is sl,e.ped as' S:n cell.,,,hose first and second o,tic3-1 di-sposed across the Path of th,e laser beam, gre ---ade)f a::-a terial transparent to laser radia-cio:, jrd th-- Inner sLiz!face of said optical windD'.'JS is shaped as a SeCDrI(JA order surfa-ve of revolution, "'U-bet JS1 hyperboloid, or sphere, while said o.,-,tic cel.' is -filled..."ith a fluid medium capable of pa-rtiall.,; zs'--sor- bing laser radiation. The PbDvesaid known device makes it possible.to obtain a smooth corneal surface of a required shape.

However, the aforesaid device suffers from an inadequately efficient use of the laser radiation energy, since part of said radiation is absorbed by the medium contained in the optic cell, whic.b prolongs the opexating time.

In addition, to T,ake the windows of the optic cell shaoed as secondorder surfaces of revolution is a technolo---ically complicated task, since the 0 Of the optic cells must be made to a pre,-sion accuracy, while any departure from a preset shape results in an affected accuracy of a preset shape of the patient's cornea. Preoperative ndjustument of the d--l:vice is a sophisticated job as well.

It is a primary and essential object of th.e inventiDn to provide a device for surgical treatmenit of ametropia featuring such a construction DIC the distributor Of laser radiation enercy density over c the laser beam cross-sectional area that would rake it possible tD UtiliZe IMIDSt efficiently the energy Of laser radiation and would at the same time be sufficiently simple in manufacture, which would ena'--le One to manufacture the device with a precision accuracy and thus to cut down the Operating time and to add to the accuracy of a preset shape of the corneal surface.

We have now discovered that the above problems can be overcome by the use of a distributor comprising laser-transparent lenses capable of focussing the beam into an annulus.

Thus. in a first aspect. there is provided a surgical laser device comprising a laser source and a beam distributor therefor, the beam distributor comprising a series of lenses capable of substantially transmitting all of the laser output directed thereon and focussing said output into a substantially annular beam.

The invention particularily comprises a first taper lens of substantially conical proportions upon which the beam can be centrally directed through the base. The result is a divergent annular beam. This can then be focussed as desired, particularly with regard the purpose to be served. preferably ablation of the cornea.

Suitable methods for focussing the resultant beam will be apparent to those skilled in the art. but it is preferred to use at least one further taper lens together with a telescopic objective to achieve a parallel beam.

It is particularly desirable to provide for the controlled movement of a second taper lens. to permit expansion and contraction of the final beam width, the preferred range being over the diameter of a human cornea.

In a preferred embodiment. there is provided a third taper lens. especially an inverted taper lens. with the telescopic objective being located between one and two. This permits focussing of the walls of the beam to a substantially 0 width at a focal plane, for greater accuracy and effect.

(2 The essence of the invention resides in the fact that in a device for surgical treatrzent of ametropia, comprising a UV pulsed laser and a distributor of laser radiation energy density over the laser beam crDsssectional area, said distributor being placed across the beam path. according to the invention, the distributor of laser radiation energy density ov er the laser beam cross-sectional area is in fact an optical systemy which incorporates arranged on a COMMDn optical axis at least two taper lenses and a telescopic objective, and is capable of transforming a parallel cylindrical laser radiation beam into a variable-diammeter annular beam, the maximum "Ai-,.meter r,f is comparable with the human's corneal diaineter.

The distributor of laser radiation energy density of the proposed device for surgical trea-.ment of amet rDpia may comprise two taper lenses having equal.

refractive angles and facing each other with their ver tices, while the telescopic objective may be situated, past the second taper lens as along the palv-,h,.-,-ay o.-IP the radiation beam.

The distributor of laser radiation energy density may also comprise three taper lenses of which the second and third, as viewed along the radiation path way, have equal refractive angles facing with their bases the laser, while the telescopic objective:7,ay be located between the first and second taper lt-nses as along the laser radiation path.

-7 l:DreDVe.rl the distributor of laser radia-Gion energy density may comprise three taper lenses facir4F,,;,ith their base laser, while the telescopic objective may be placed between the first and second lenses, as along the laser radiation path, and the rnird lens, as along the laser radiation path, may be in fact an inverted cone and have a refractive angle equal to 900-iC $ where 01 denotes the refractive angle of the second lens as along the laser radiation path.

It is ex pedient, for all embodiments of the inventiong that the second taper lens, as along the laser radiation path, be movable along the optical axis.

The device for surgical treatment of ametropia, according to the present invention, makes it possible to attain highe-r accuracy of a preset corneal shape due to a substantially cut down Dperetin.--- Such a curtailing of the operative time results from the fact that the entire radiation flux erritted 10,v ube laser acts upon the cornea] surface beine, treated at each instanr of time, while energy loss ir, zhe distributor of laser radiation energ.... density of the proposed device is minimized. Besides, the proposed device is readily amenable to adjustment for a preset amount of ametropia correction,said adjustment being effected by moving one of the taper lenses of said distributor with the aid of a stepped electric motor. To manufacture the taper lenses is a simpler tec,nDID- 9 gical task as compared with the manufacture of c;l.ie cell are in fact second-order surfaces of revolution; so the device, according to the invention, is simpler in manufacture and can be made to an adequate degree of accuracy.

In -z..hat follows the invention will be eluc,-.da-ued by a description of some specific exemplary embodiments thereof with reference to the!iccompanying draviin,::.s,.herein:

'FIG. 1 is a dia=,rairmatic view of a device for sur- -7j..cal treatment of ametropia, according to the invention, in its e,-- "oodiment comprising two taper lenses; FIG. 2 is a view of an embodiment of a device of FIG. 1, comprising trzee taper lenses; FIG. 3 is a view of an emblodiment of a device of FIG. 2, featuring its third lens shaped as an inverted cone; FIG. 4 is a schematic view of a patient's eye at the staje of myopia treatment with the aid of the -e,,,,'Lce shown in FIG. 1; FIG. 5 is the same as in FIG. 4 for hypermetropia treatment; FIG. 6 is a schematic view of a patient's eye 3t the sta,.e of myopia treatment with the aid of the devi-ces C) shown in FIG. 2 or FIG. 3; and FIG. 7 is the same as in FIG. 6 for hype rzetropia treatment.

4 9 The device for surgical treatment of ametropia, that is, myo'Dia and hypermevropia, as shown in comprises a UV pulse-d laser 1 and a distributor 3 of the density of energy of radiation of the laser 1 over the cross-sectional area of a laser beam 2, said distributor 3 being placed across the path of the Laser beam 2 so as to determine the diameter of the zone of surgery on a patient's cornea 4.

The distributor 3 of laser radiation energy den- sity is in fact an optical system incorporating two taper len-les 5 and o- arraajed in tanderd on a common optic axis, said lenses facing each other with their vertices and having equal refractive angles and a telescopic objective 7 situated past the second taper lens ' as along the path of the radiatJon of the 1-ser 1.

0 L - All the optic elements mentioned aove 3re made of a material transparent to laser radiation, e.g., of quartz. The second taper lens OG, as along the path of laser 2adiation, is traversable along the optical axis with, aid of a stepped electric motor 8 as in the embodiment described herein, and estaolishes, to-ether..jith the first Laper lens 5, a pancratic system. The telescopic objective 7 consists of a train of convergent lenses 9 and.a train of divergent lenses 1J, ooth being calculabed with due account of minimized aberration and being in a general case a variable-magnification telescopic system ( C FIG. 2 illustrates an embodiment of the hereinproposed device for surgical treatment of ametropia, wherein ilv-s distributor 3' of radiation energy density comprises three taper lenses 5, 11, 129 all of them facing v..ith their bases the laser 1 and having, equal refra.ctive angles and a telescopic objective 13 inter Dosed between the first lens 5 and the second lens 11 as along the path of 'the radiation emitted by the laser 1.

All or-,tiG elements in said embodiment of the device are also made of a Material transparent to laser radiation, such as quartz,, ihile the second taper lens 11 as alonG the path of laser radiation, is movable aling the opuical axis from the stepped electric motor 8. The telescopic objective 13 is consti=ted by a dlivergent lens 14 anJ a-, M cow,er.--nt lens 15, both being also calculated j.,ith all-jwance for minimized aberration.

FIG. 3 presents another embodiment of the hereirn- proposed device for surgical treatment of ametropia, c wherein its distributor Y of radiation energy density 2 0 incorporates also 'three taper lenses 5, 11 and 16, all of them facing with their bases the laser 1, and a tele scopic objective 1 1 comprised of a divergent lens 141 J 3 and a convergent lens 15', the parameters of said lenses being other than those of the elements of t-he -telescopic lens 13 (FIG. 2), the telescopic objective 13' oeing interposed between the first taper lens 5 (FIG. 3) and A the second taper lens 11 as along the path of the radiation emitted by the laser 1. Unlike the embodiment. of the device mentioned above, the third taper lens 16 features inverted conicity and its refractive angle equals 9JO- c-, where --v- is the refractive angle of the first taper lens 5 and the seocni. taper lens 11 as along the path of laser radiation. All optic elements of the distributor Y1 are likevilse made of a material transparent to laser radiation, e.g., qu--,rtz, -whereas the second taper lens as along the path of laser radiation is traversable along the optical axis vjith the aid of the stepped electric motor 8.

To select,,.,hat an ar,.bodi,-iient of the device for sur;.ical treatment of ametropia is to be used depends on how producible is said device and on the requi-rement. as for min-Lmized aberration of -che optical system of device.

The device -oresented in FIG. 1 is -,iore sp3ce-sivJ-riS but needs hisher accuracy of manufacture and is CD difficult to adjust. The embodiments of the device ris .4 c:) shown in FIGS 2 an' 3 Provide for higher accuracy o_ urgery, since they make use of focused radiation be=s and feature the minimized aberration of -their opt cal sy..,ter,. The device depicted in FIG. 3 is More compact that shown in FIG. 2 though provision of the invertuedconicity lens 16 therein complicates much its produc-cion technology.

1 z - The device for surgical treatment of ametropia, according to the inventiong operates as follows.

Operation of the device as shown in FIG. 1 mill hereinafter be considered with reference to treatment of myopia.

It is common knowledge that the corneal surface of a normal eye can be described by the equation of a paraboloid of revolution having a radius R of curvature.

The corneal surf ace 4 (PIGS 4, 6) of an eye af f e c- ted by myopia is also described by the equation of a paraboloid of revolution having a radius R M of curvauure at Cs vertex less than in the case of a normal eye, i.e., R1 m < R.

For surgical treatment of myopia a layer should be removed from the cornea, said layer being bounded by two parabolic surfaces differin5 in curvature and appearing as a hatched segwent 17.

When treating myopia the parallel cylindric31 radiation beam 2 emerging from the laser 1 (FIG. 1) and fea- turing its energy density uniformly distributed over the beam cross- sectional area (i.e., a circle with a diameter D), passes through the first taper lens 5 and is trans- Cormed into a cone-shaped beam 18 featuring the cone wall thickness equal to D/2.cos (b and an included angle 2 v p of the cone-shaped beam, which depends on the refrac- tive anplec>i and a refractive index In' of the taper k, 1 1,5 le ns 5:

sin,b= (nfl - sin2d. 1 - n2S,.n; o(). sin oC (1 Fulpther on the laser beam 18, while passing through the second baper lens 6 having, the same refractive angle oL is transformed into an annular beam l, featurin--, the thickness of annulus wall equal -uo 1)/2, %,1Ale with the taper lens 0' steplessly moving along, the optical axis by virtue of the stepped electric r,,,oto.r 3, the thus-formin- anna1F,,r beam smoothly chanGes i'u-s outside diameter DI Provision is made in the proposed embodinent of tIne device for a possibility of adjustin- the value of:l,--th-Ln the lii. its of a ringhaving the minimum dia,.ieter D (that is, when t-he ring is transformed into a circle and the rin_ diameter equals zero) and a raaxirrum-size ring, having an ou-uside dia--e- ter Dmax, while -the value of D, is related to -the tra 1 1 velling of the taper lens 6 by the followinz. equality:

D1 = D + 2,1. t:- where is the amount of displacement of the -taper lens 6 from its zero position (shovV,n at Ref.

No.61 in FIG. 1), wherein D 1 =1'il said e-uali-ty holding true when a distance 'a' between the vertices of the taper lenses 5 and 6 is selected according to the followiri;5 expression:

2.5 D (L D o_ D 2 2 1 it where D. is the diamet,3r and L, the thickness of the taper lens Having passed through the second taper lens 6 the parallel radiation beam 19. whose cross-sectional area is ann,-lar-shapedy travels throu.,,h the telescopic objective 7, in which said beam is transformed, with a 'Kt, likewise into a parallel annalar beam 20 having a variable outside diameter D2 and a wall thickness Id'. Then the beam 20 is directed im- ledia-tiely onto the cornea 4. The thickness Id' of the wall of "Uhe beam 20 is changed by steplessly varying 0 W the distance between the lenses 9 and Ii of the telescopic objective 7.

Thus, D1,,=DI K, where K is the magaificat-lion factor, which is less than unity, i.e., c -----oss-sectional area of the beam 20 changes within the limits of the ring., of a maximum diameter equal to D2=Drinax, K and a 1 having a maximum diameter of D 2 = DK. In this case the diameter of D = Dmax. K is comparable ivith the diaMeter 2 1 2,3 of the patient's cornea 4.

The thickness Id' of the wall of the ann-,lar beam 2i is selected so as to suit the conditions of surgery and.the parameters of the laser 1. It is desirable in this case to select the rdnimum possible value of Id' 25with due account of the diffraction characteribties of the radiation energy density distributor 3.

.1j.hen u;i-ng the embodiment of the device, as shown in FIG7. 2, for treatment of myopia the parallel beam 2 emerging from the laser 1 and featuring i-cs energy density distribated uniformly over the cross-section having the diameter D passes, like in the precedirLZ embodiment, through the first;aper lens 5 and is trans formed into the cone-shaped beam 18 having the cone wall thickness eq,,i-E31 to I1J/2 cos and an included angle 2 of the cone-shaped beam. Further on the beam 18, while passing, ul,,--o-Lzjh the train of the spherical lenses 14 and '15 that constitute the telescopic lens 13, is trans form.ed into an arunular beam 212 having a constant a.verace diameter and a diminishing thickness, a focal plane 21 of said beam 212 intersectinS the surface of the cornea 4 and being sq:aare mith the o-itical axis of the device.

Then the annular beam 22, upon Dassiri, the telescopic ob-ective 1 travels through a cone-shaped vari.-ole L; 39 W ma-nif ication telescopic system consei-:.-,azed by the taper lenses 11 and 12,,v,herein said beam is first urans formed into a cone-shaped beam 23 and then into an a.,inu lar jeam 24 having a variable diameter D. and a dimi nishing thickness Id' of its wall.

The minimum cross-section of the beam 24 is essentially a circle with a diameter of 2d, the value 23 Of Id' being selected so as to suit the conditions (0 of sur.:'ery and the parameters of the 'Laser of the c 71 disr,ributor Y. The value of Id' is selected to be the minimum possijle and is largely determined by the diffraction characteristics of the distributor 3 The diameter D2 is chan.ged to a required value which is attained by smoothly travelling the taper lens 11 alon.,. the optical axis with the aid of the stepped electric motor 8.

-T Ir, the embodiment of the device shown in 'EIG. 39 o-oeration of the rad-.3-JL-.ion enerl-Y density distributor Y' Q di-f:-ers from that of the distribu-Gor 3' of FIG. 2 in that the annular beam 22, u1Don passing, through the zelescopic obective 131, travels through a cone-shaped tuelescopic system established by the taper lenses 11 and 16, the latLer lens having inverted conicity, -.r.'.-lerein s-fmi-- J beam is also transformed first into a cone-shaued beam 2then into an annular beam 26 havin':;, a variable dia....-1t3r and the thickness Id' of its wall diminishir.:, as alonthe radiation path. The minimum cross- sect-iz-on ol z;ail.-J beam is also in fact a circle with a diameter of 2d, while 'the Daran. eters of the beam 26 are also chan,;ed by smooth movement of the taper lens 11 along, the optical axis with the aid of the stepped electric. motor 8.

The distributor Y' of FIG. 3 is more compact han the distributor 3' of FIG. 2, since with the maximum values 0 1-1 of the diameter T"Max of the annular beams '224 2) LJ 2 and 26 (FIG. 3) directed onto the cornea 4, a distance 'cl between the bases of the taper leases 11 and 16 that constitute the cone-shaped telescopic system in the distr-ibutor Y', is at all times shorter than a distance Ibl between the bases of the leases 11 and 12 U U U in the distributor Y, that isy an inequality c < b is always satisf ied.

It is cow,,.non knoviled,e that exposure of biol)- ical tissues tD tl.--Lee-;L7..L2ect of remote UV radiation resulzs in ablation (evaporation) of such tijsues, w.-.ile t-he t'-,-.,ickness of the tissue layer bein,5 ablaued is in direct proportion to the --rier--.y density within a certain ran-7e of the radiation energj density values.

In the course of surwery, interaction of -uh-- fective laser radiation beam 20 (FIG. 1),,,ith the cornea 4 results in removal of the seE;.,iient 17 4). The siEn-Jlar segment 17 (FIG. 6) is removed also due to in'u-eracuior, of the beams 24 (FIG. 2) and 20' (FIG. 3) the cornea 4. Irradiation starts from the central zone of the cornea 4 with the maximum diameter of' the e-L-:'ect'Lve radiation beam and is carried out in such a P,,ianner that -L the exposure time is reduced as the dia-"eter of the eo fective beam increases. Appropriately selected irradiation conditions results in removal of the segment 17 (FI3XS 4 1 C3 and 6) of the cornea 4, which is bounded by two parabolic surfaces of revolution of mhich one is the myopia-affected corneal surface, while the other is the surface of the cornea 4 after its havind- been exposed to the effect of the radiation of the laser!.(FIGS 1, 29 3). Irradiation is carried out prior to elimination of myopia (i.e., the h--tehed s-egment 17 in FIGS 4, CES).

The corneal surface of a hypermetropic eye is described by the equation of a paraboloid of revolution having.3 radius R, of curvature qt the vertex exceedin:, that in the case of a normal eye, i.e., R, > R. For 5 surgical treatment of h-permetropia a layer shoul.-AJ be C) 1:

removed fro.,,,, the cornea 4, which is bounded by tv,,o d.--oferentcurvature parabolic surfaces, i.e., a seo-inent 27 (FIGS 5 and 7). Surgical treazument of h-iDer- m u_ 2etroDia is carried out in a way similar to that described for myopia, the sole difference residin in the fact that irradiation of the co2nea 4 s-tarts from its periphery, with the maximum diar.,iete-- of the ef- fective radiation beam, and is performed with -radually reduced both the eflective beam dia-.--ter and the i_---radiation time.

To promote understanding of the essence of the present invention, given bel-)w is a specific e-lr.e.:,.plary 2- embodiment thereof.

1 1 1 19 An embodiment of the device for surSiGal treatwent of ametropia, accordinwa to the invent'on, as sho.,.,,,n in FIG. 3 has been manufactured and tested. In order to alter the eye refraction of a test rabbit use was made of the radiation of the excimer laser 1 on A+F molecules and a lxjave'erll-,.'th of 193 nm, shaped into a parallel cylindrical beam havincr a diameter D = 6 mrat A, 4 All stacic el-.-.en'-s of the "J..qtributor Y' of radiation energy density nere made of optic quartz 0 (rl = 1.559).

The first taper lens 5 having 3 convex sur-face (i.e., direct conicity) and a refractive angle c-lc = 100 and the third taper lens 16 having inverted conicity and a ref ractive an71e M -o( =760 viere fixed stationary, 1,v,hereas the second taper lens 11 havinj, direct conicity and a refl-active angle cC =141 travelled alon.. the.)nuicgl axis for a distance e- 150 mm, enabled the -jnlue O.L to be adjusted within 8 and 0. 5 mn-, rin ,,uall thickness d = 0.25 an, = const in the plane of t-he radiation effect.

0 The repetition frequency of the radiztiori pulses emitted by the laser 1 equalled 15 Hz, the pulse ener-y changing within IJi and 300 MJ. As a result of procedures on 16 eyes of 8 experimental rabbits there was attained an alteration of the corneal refract-.on within 0.5 and 5 dioptres depending on the pararnet-ers of the radiation effect applied.

-o practical application of the device, according to the inventiong makes it possible to enhance the accuracy of a preset shape of the treated corneal surface eight- to tenfold as compared with the similar device having a changeable diaphragm, to cut dorn the operating time seven-toeijht-fold, as against the aforesaid device and three- to four-fold as compared with the device, wherein the distributor of radiation energy density is in fact an opLic cell. an enhancement of the accuracy of a preset the treated corneal surface occurs largely due to a substantially curtailed operating 02e, which in tarn resulbs from the fact that the entire radiant flux emerging from the laser 1 acts on the surface of Ij the cornea 4 being treated at every instant of time.

10. Such shane of 1 M&C FOLIO: 230P60473

Claims (14)

1. WANGDOC: 02BOD 1. A surgical laser device comprising a laser source and a beam distributor therefor, the beam distributor comprising a series of lenses capable of substantially transmitting all of the laser output directed thereon and"focussing said output into a substantially annular beam.
2. 2. A device according to claim 1, the distributor comprising at least one taper lens.
3. 3. A device according to claim 1 or 2, wherein the beam is focussed substantially parallel.
4. 4. A device according to claim 1, 2 or 3. the distributor further comprising a telescopic objective.
5. 5. A device according to any preceding claim, comprising 2 or 3 taper lenses.
6. 6. A device according to any preceding claim. wherein the width of the beam wall diminishes away from the final element of the distributor to a focal plane.
7. 7. A device according to any preceding claim wherein the width of the annular beam is adjustable between at least a range wherein the distance between walls of the beam is substantially 0 and an overall diameter of about the diameter of the cornea of a human eye.
8. 8. A device according to any preceding claim using pulsed UV laser light.

   1 PIQ
9. 9. A surgical device comprising a UV pulsed laser and a beam distributor therefor located across the beam path, the distributor having, on a common optical axis, at least two taper lenses and a telescopic objective, and being capable of transforming a parallel cylindrical laser radiation beam to a maximum value comparable with the diameter of a patient's cornea.
10. 10. A device according to any preceding Claim, wherein the distributor comprises two taper lenses having equal refractive angles and with vertices facing each other, the telescopic objective being distal to the second lens along the laser path.
11. 11. A device according to any of Claims 1 to 9, wherein the distributor comprises three taper lenses, bases to the laser source, the second and third lenses distal to the source having equal refractive angles, the telescopic objective being interposed between the first and second lenses.
12. 12. A device according to any of Claims 1 to 9. wherein the distributor comprises three taper lenses, bases to the laser source, the telescopic objective being interposed between first and second lenses distal to the source. the third lens being shaped as an inverted cone 0 and having a refractive angle of 90 -a, where a denotes the refractive angle of the second lens.
13. 13. A device according to any preceding Claim and comprising at least 2 taper lenses. the second lens being movable along the optical axis.
14. 14. A laser device. comprising at least one taper lens, substantially as described hereinbefore with particular reference to any of the accompanying Figures 1 3.

    Published 1990 C.ThePatent Office, State House. 6671 High Holborn. London WC1R4TP- Purther copies maybe obtained from The Patent Office Sales Branch, St Mary Cray. Orpington. Kent BR5 3RD. Printed by Multiplex teclimques ltd. St MarY Crky. Kent. Con- 1'87 1