WO1996021407A1

WO1996021407A1 - Integrated laser reprofiling systems

Info

Publication number: WO1996021407A1
Application number: PCT/US1995/017027
Authority: WO
Inventors: Marc D. Friedman
Original assignee: Summit Technology, Inc.
Priority date: 1995-01-11
Filing date: 1995-12-28
Publication date: 1996-07-18
Also published as: AU4530696A

Abstract

Apparatus and methods are disclosed for reprofiling a surface (e.g., the cornea of the eye) by ablation. The apparatus is positioned between a source of ablative radiation and a surface so that the exposure area of the surface to which the radiation is delivered may be varied. In one embodiment, a masking means having apertures of predefined shapes is provided to selectively pass a portion of the radiation and drive means is employed to move the masking means across the beam of radiation in two different directions, thereby effecting two patterns of ablation at the surface, such that the cumulative effect of these two patterns is the selective ablation and reshaping of the surface.

Description

INTEGRATED LASER REPROFILING SYSTEMS

Background of the Invention

The technical field of this invention is laser ablation of surfaces and, in particular, the invention relates to the use of apertures of predefined shapes and to mechanisms that achieve predetermined patterns of reprofiling in surfaces, especially delicate biological surfaces such as the cornea of the eye.

The cornea of the eye is composed of five distinct layers: the outer epithelium; an anterior elastic lamina known as "Bowman's layer"; the cornea proper (or "stroma"); the inner endothelium; and a posterior elastic lamina known as "Descemet's membrane". The stroma is fibrous and transparent and constitutes the major portion of the cornea. Bowman's layer, which forms the outer elastic lamina, is a rigid fibrillar structure not tending to cut or fracture, while Descemet's membrane, which forms the inner elastic lamina, is very brittle but elastic and has a tendency to curl. Together, the Bowman's layer and Descemet's membrane impart the necessary curvature to the stromal tissue. The cornea along with the lens of the eye form a refractive system which images objects onto the retina.

The three most common refractive vision defects are hyperopia, myopia and astigmatism. When the eye's refraction system is hyperopic, the ability to see at close range is impaired. Rays of light coming from nearby objects cannot be focused on the retina, whereas rays coming from distant objects can be properly focused. As a result, close images are blurred and distant ones are clear. In a hyperopic lens system, the corneal curvature typical is too flat. The condition is usually correctable by use of spectacles having convex lenses (thicker at the center than at the periphery). In an opposite fashion, myopia or nearsightedness occurs when the corneal curvature is too steep and focuses the light rays before the retina. This condition is usually corrected with the use of a concave lens (thinner at the center) of the proper dioptric power.

Astigmatism is a condition in which the cornea lacks spherical symmetry. Instead the cornea typically has a cylindrical or elongate profile, so that the radius of curvature of the cornea measured along one axis is different from the radius of curvature of the cornea measured along a perpendicular axis. The conventional approach to correction of astigmatism is to employ a complementary asymmetric lens which compensates for the aspherical shape of the cornea. Often patients will present astigmatism along with myopia or hyperopia as well. In the field of surgery, a known technique for treatment of certain forms of refractive errors, such as acute myopia, hyperopia and astigmatism, is to surgically remove an anterior segment of the cornea down into the stroma, to reshape the removed segment as by surgical grinding in a frozen state, and to restore the reshaped segment into the eye. In this type of operation, known as keratoplasty, the eye heals by reformation of the outer epithelium layer over the reshaped stroma. Alternatively, a layer of the cornea can be opened up as a flap, an artificial or donor lenticular implant then inserted under the flap, and the flap sutured up again.

Other surgical techniques for altering the corneal surface to correct refractive errors have also been proposed. One increasingly common technique is Radial Keratectomy ("RK") in which a set of radial incisions, i.e., resembling the spokes of a wheel, are made in the eye, down into the stroma, to remedy refractive errors such as myopia (nearsightedness). As the incisions heal, the curvature of the eye is flattened, thereby increasing the ocular focal distance. The operation is not particularly suitable for correction of hyperopia

(farsightedness) and can pose problems if the surgical incisions are uneven or too deep.

Until recently, surgical operations on the cornea were most commonly carried out using diamond or steel knives or razors, and such techniques continue to be practiced. For example, use of a physical cutting tool is still widespread in corneal operations such as keratoplasty and lenticular implants. (See, generally, Binder et al, "A Refractive Keratoplasty," 100 Arch. Ophthalmol.. 802 (1982) and "Refractive Keratoplasty Improves With Polysulfone Pocket Incision," Ophthalmology Times (July 1, 1986)).

Use of the laser beam as a surgical tool for cutting non-ocular incisions, a so-called

"laser scalpel", has been known for some time. (See, for example U.S. Patent 3,769,963 to Goldman et al). However, the utility of most forms of laser radiation for corneal surgery is compromised by the tendency of laser beams to cause thermal damage and, consequently, scaring and opacification in the extremely delicate structure of the corneal stroma.

Even "cold" photoablative UV radiation from excimer lasers and the like must be carefully controlled to avoid permanent damage to the eye. (For a study of damage which can be inflicted on the cornea by exposure to uncontrolled excimer laser radiation, see Taboada et al, "Response of the Corneal Epithelium to ArF Excimer Laser Pulses," 40 Health Physics 677-83 (1981)). Nonetheless, the use of excimer laser radiation to replace conventional physical cutting tools in many corneal surgical procedures holds significant promise. A new technique for corneal reshaping known as photorefractive keratectomy ("PRK") involves the use of an excimer laser photoablation apparatus in which the size of the area on the surface, to which the pulses of laser energy are applied, is varied to control the reprofiling operation. In one embodiment, a beam-shaping stop or window is moved axially along the beam to increase or decrease the region of cornea on which the laser radiation is incident. By progressively varying the size of the exposed region, a desired photoablation profile is established on the surface. For further details on this technique, see Marshall et al, "Photo- Ablative Reprofiling of the Cornea Using an Excimer Laser: Photorefractive Keratectomy," 1 Lasers in Ophthalmology. 21-48 (1986), and U.S. Patent No. 4,941,093 issued to Marshall et al. herein incorporated by reference.

Another new PRK approach to corneal reshaping involves the use of a laser photoablation apparatus in which a beam-shaping mask is disposed between the laser and the surface. In one embodiment, the mask provides a predefined profile of resistance to laser radiation whereby a portion of the laser radiation is selectively absorbed and another portion is transmitted to the surface in accordance with the mask profile. For further disclosure of such masking techniques, see U.S. Patent No. 4,856,513 issued to Muller, U.S. Patent No. 4,994,058 issued to Raven et al., and U.S. Patent No. 5,019,074 issued to Muller also incorporated herein by reference.

It also has been suggested that controlled ablative photo-decomposition of one or more selected regions of a cornea can be performed using a scanning action on the cornea with a beam from an excimer laser. (See, for example, U.S. Patent 4,665,913 issued to L'Esperance on May 19, 1987). In the L'Esperance patent, it is suggested that myopic and hyperopic conditions can be reduced by repeatedly scanning the cornea with an excimer laser beam to achieve penetration well into stroma and to induce resculpting of the stroma tissue.

Yet another PRK technique, disclosed for example, in U.S. Patent No. 4,729,372 issued to L'Esperance attempts to control the exposure of the laser light by using rotating disks having apertures or annular openings of different diameters. A shortcoming of such rotating disk systems is that even a slight misalignment of the laser, the aperture and the eye can adversely affect the outcome. Additionally, the disks either must be custom fit to a particular refractive error or more than one disk must be used to correct specific conditions.

Apart from the use of photodecomposable masks, all of the mechanical PRK systems described above require considerable alignment of optical elements and programming or substitution of additional elements to address astigmatic conditions as well as myopicOr hyperopic corrections. Therefore, it is the object of the invention to provide an integrated apparatus and methods to perform myopic, hyperopic, and astigmatic corrections of desired dioptric values. It is a further object of this invention to perform these corrections simply and with ease of alignment.

Summary of the Invention

Apparatus and methods are disclosed for reprofiling a surface (e.g., the cornea of the eye) by ablation. The apparatus is positioned between a source of ablative radiation and a surface to be reprofiled so that the area of the surface exposed to the delivered radiation may be varied. A mask having apertures of predefined shapes is provided to pass a portion of the radiation. The apparatus can further include a drive mechanism to translate the mask in two orthogonal directions across the delivered beam, thereby effecting two patterns of ablation on the surface. Each such pattern of ablation alters the profile of the surface relative to one axis. The combined effect of these two patterns achieves desired reshaping of the surface.

In one embodiment, a single mask is attached to a drive mechanism capable of linearly translating it. The mask and the translational mechanism are attached to a rotational mechanism that can rotate the mask through the appropriate angle suitable for performing a second translation with the same mask. Alternatively, two separate masks which are independently translated can be used.

The present invention is particularly adapted for hyperopic and/or astigmatic corrections which generally consist of steepening the curvature of the surface of a cornea. The desired change in dioptric power achieved by the correction is controlled by the fluence or energy density of each laser pulse delivered and the number of pulses distributed across the cornea during translation. During corneal reprofiling operations, the mask can be translated by a series of equally-spaced ministeps across the optical zone of the eye, e.g., a circular area of about 3 to about 8 mm in diameter. The speed of the translating steps and/or the number of laser pulses which reach the cornea during each step determine the amount of ablative laser radiation which will impinge upon each section of the cornea during the operation. Alternatively, the mask can be translated in a continuous fashion across the optical axis. In either procedure, the depth of ablation and the shape of the reprofiled surface can be accurately controlled.

Applying ablative radiation to the eye via a mask that is translated along two orthogonal axes is particularly suitable to correcting astigmatic conditions, since transforming an astigmatic profile to a spherical profile requires more ablation along one axis than along the other. If the output power of the radiation source is constant, the amount of ablation achieved along each axis can be controlled simply by varying the speed at which the mask is translated. Translating the mask more slowly exposes the surface to more radiation and therefore results in more ablation. By translating the mask at one speed along one axis, and at another speed along the perpendicular axis, an astigmatic profile can be transformed to a spherical profile. Alternatively, the desired correction can be performed by translating the mask at constant speed and increasing the laser output power while the mask is translated along one of the axes. Typically, one axis is chosen as the meridian of the cornea that has the steepest radius of curvature. The other axis is then chosen as perpendicular to the first axis.

The mask of the present invention includes at least one hyperopic-astigmatic correction aperture. In one embodiment, this aperture can consist of a combination of two parabolic contours overlapping with a circular annulus. One parabola useful to delineate the contours of the aperture is defined in Cartesian coordinates by the formula:

y(x) = K(x /R²)

where K is a constant related to R, the radius of curvature of the surface to be reprofiled. The parabolic portion of the hyperopic-astigmatic aperture is used to perform a hyperopic- astigmatic correction. The annular portion of the hyperopic-astigmatic aperture is used to create a blend zone at the periphery of the corrected portion of the cornea.

According to another aspect of the invention, a three-aperture mask stage is provided. In addition to the hyperopic-astigmatic aperture, the stage can also include a second clear or circular aperture to accommodate myopic corrections and a third aperture for Partial External Trabeculotomy (PET) operations which can relieve glaucoma conditions.

The three-aperture mask stage can be used in conjunction with an adjustable iris. In practice, the iris remains in a fixed position centered on an optical axis which defines the alignment between the surface to be reprofiled and the laser. To perform a surgical procedure, the mask stage is translated to align the appropriate aperture with the optical axis. The iris blocks the light from the other apertures, and allows only light passing through the appropriate aperture to reach the eye.

When performing myopic corrections, the mask is disposed in a fixed position which aligns the circular aperture with the iris mechanism to define an optical zone diameter on the surface to be reprofiled. The iris mechanism is then progressively closed (or opened) to impart more ablative radiation to the center of the optical zone and less radiation to the periphery. This flattens the curvature of the cornea and thus creates the desired correction. When performing a PET procedure to relieve a glaucoma condition, the PET aperture is aligned with the Canal of Schlem region of the eye. This canal is the duct that allows the flow of the vitreous fluid around the iris of the eye. When this canal is obstructed, intraoccular pressure builds up. The persistence of the high pressure can precipitate a glaucoma condition. The channel created by projecting a laser beam through the PET aperture relieves intraoccular pressure.

In one method according to the present invention, hyperopic-astigmatic correction procedures are performed by (a) adjusting the iris to match the optical zone denoted by the outer diameter of the parabolic portion of the hyperopic-astigmatic correction aperture, (b) performing a hyperopic-astigmatic correction of desired dioptric value by translating the aperture along a preferred axis, (c) halting the delivery of laser pulses and centering the annular part of the astigmatic correction aperture with the optical zone, (d) resuming the delivery of laser pulses and progressively opening the iris to its widest opening to create a blend zone at the periphery of the hyperopic-astigmatic correction, (e) halting the delivery of laser pulses and rotating the aperture to the orthogonal axis, and (f) repeating steps (a) to (d) along the second axis to complete the correction. Alternatively, the cylindrical reprofiling operations along each of the two axes can be performed first and then the annular aperture can be disposed in the beam path to effect a blend zone by opening the iris as a final reprofiling step.

Creation of a blend zone, as described above, provides a smoother transition between the reprofiled portion of the cornea and the surrounding peripheral regions, the blend zone inhibits epithelial cell regrowth which would otherwise diminish the accuracy of the correction. The epithelium regrows almost immediately following photorefractive keratectomy ("PRK") operations and within days forms a new layer of transparent tissue covering the reprofiled corneal surface. Upon regrowth, the epithelium tends to fill and smooth out sharply defined patterns, such as those produced by an astigmatic correction. If new epithelial tissue fills the sharp edges of the correction, the effectiveness of the correction will be diminished. Thus, the creation of a blend zone is desirable to insure that upon cell regrowth, the accuracy of the astigmatic correction is maintained.

The invention will next be described in connection with certain illustrated embodiments; however, it should be clear that those skilled in the art can make various modifications, additions, and subtractions without departing from the spirit or scope of the invention. Brief Description of the Drawings

FIG. 1 is a diagrammatic illustration of a system for reprofiling a surface by laser ablation, in accordance with the invention;

FIG. 2 is a schematic illustration of a simple mask for performing hyperopic and astigmatic-hyperopic corrections of surfaces; FIG. 2 A is a schematic illustration of the mask useful in performing hyperopic, astigmatic-hyperopic, myopic and/or PET correction of surfaces;

FIG. 3 is an iris mechanism for use in conjunction with the mask of FIG. 2A;

FIG. 4 is a schematic illustration of one embodiment of a reprofiling apparatus according to the invention, showing two simplified masks capable of being translated in orthogonal directions;

FIG. 5 is a schematic illustration of another preferred embodiment of a reprofiling apparatus according to the invention, showing one simplified mask, a translation mechanism, and a rotation mechanism that allow a reprofiling operation in a sequence of two steps;

FIG. 6A is a top view of the hyperopic-astigmatic aperture positioned over the surface to be reprofiled; FIGS. 6B-6E are "snap shots" of the areas of the surface that are exposed to ablative radiation during a translation procedure according to the invention;

FIG. 7A illustrates a hyperopic surface; FIG. 7B illustrates the ablation achieved on the hyperopic surface by translating the parabolic portion of the hyperopic-astigmatic aperture across the iris; FIG. 7C illustrates the creation of a blend zone by use of the annular portion of the hyperopic-astigmatic aperture;

FIG. 8 is a top sectional view of the masking apparatus shown in FIG. 5;

FIG. 9 is a cross sectional side view of the apparatus of FIG. 8; and

FIG. 10 is a three-dimensional graph representing the profile obtained as a result of a sphero-hyperopic correction by a system in accordance with the invention. etailed Description

FIG. 1 is a functional diagram of a system 10 according to the invention, used for reprofiling surfaces by laser ablation. It includes a source 12, for example, an ArF excimer laser emitting energy at a wavelength of about 193 nanometers. Alternatively, the laser can be another high energy, pulsed or continuous wave laser or non-coherent radiation source that likewise permits non-thermal ablation of thin layers of tissue. The system 10 further includes beam-forming optics 17, as are known in the art, to crop the beam edges, homogenize the beam profile and/or compensate for beam divergence. The ablative radiation then traverses the beam shaping optics 14 comprising translatory mask 32 and iris 16. The pattern coming out of the beam shaping optics 14 can then be imaged onto the surface 22 of eye 26 by means of the relay /projection optics 28, or can be projected directly onto the corneal surface 22, if the beam is sufficiently collimated as a result of the forming and/or shaping operations. The source 12 can be controlled by a control element 13 which can be adjusted to cause the radiation source to produce pulses of light at a specific frequency and intensity. To further control the radiation source, a feedback monitor device 15 can be provided which receives information from the translating mask 32 and/or the adjustable iris 16, and/or the surface to be reprofiled 22. The feedback path 18 communicates with the feedback monitor 15 and transmits control signals via path 20 to the control element 13.

In FIG. 2, a simple translatory mask 32 according to the invention is shown having a double parabolic aperture 34. (This parabolic aperture is also referred to in the specification below as being "hour-glass" shaped or "butterfly" shaped.) The opening 34 is designed to provide cylindrical correction to a target surface when translated across the path of a beam of ablative radiation otherwise impinging on the target surface.

FIG. 2 A is a schematic diagram of another embodiment of the translatory mask 32 according to the invention. The mask 32 includes three apertures 36, 37, 38 for use in different reprofiling procedures. The circular aperture 38 is used in conjunction with an adjustable iris (not shown) to create a light pattern suitable to perform myopic corrections of corneal surfaces. As explained above, the rectangular aperture 37 is used in partial external trabulectomy (PET) procedures implemented to relieve the intraoccular pressure associated with glaucoma conditions. The third aperture in translatory mask 32 is the hyperopic- astigmatism correction aperture 36.

Hyperopic-astigmatism aperture 36 has a parabolic portion 34 (similar to that described above in connection with FIG. 2) as well as an annular portion 35. Translating parabolic portion 34 of aperture 36 along one axis achieves a hyperopic-astigmatic correction (cylindrical correction). The combination of two such corrections performed along orthogonal axes will produce a sphero-hyperopic correction. Annular portion 35 of aperture 36 is used to create a "blend zone" (i.e., to smooth the region between portions of the surface that have been ablated and portions that have not been exposed to radiation).

As shown in FIG. 2A, mask 32 can be mounted on stage 90. Mask 32 can be translated by translating stage 90 via rack 92 and gear 93. Gear 93 can position any of the three apertures 36, 37, 38, above iris 16 (not shown), and can also translate the parabolic portion 34 of aperture 36 across iris 16 for use during hyperopic-astigmatic correction procedures. Gear 93 can be driven by various conventional motors, available, for example, from Inland, Inc.

FIG. 3 illustrates iris 16. In use iris 16 is disposed between translator mask 32 and the surface to be reprofiled 22, as illustrated schematically in FIG. 1. During surgery to perform myopic corrections, translatory mask 32 is translated so that circular aperture 38 is aligned with iris 16. Increasing the opening of iris 16 during delivery of laser light to the surface to be reprofiled 22 results in more ablation of the center of the optical zone and less ablation in the periphery. This flattens the curvature of surface 22 thus performing the desired correction.

Iris 16 can also be controlled by a conventional motor and controlled via a 25-pin connector 75. By way of example, the control motor is also available from Inland, Inc., and the iris diaphragm can be a # 041DC009 adjustable iris manufactured by Melles Griot of Irvine, CA. As this figure illustrates, the iris diaphragm 16 has a plurality of pivoting leaves 76 actuated by a pin 77 and controlled by the control motor. The initial position of pin 77 can be adjusted via rod 78, spring 79, and set screw 80.

FIG. 4 is a schematic diagram of a system IOA according to the present invention employing dual translatory masks. System 10A includes a masking apparatus 30 comprising two translatory masks 32a, 32b oriented orthogonally to each other. This figure shows the radiation source 12, the iris 16 and the imaging optics 28 defining an optical zone diameter 21 on the surface to be reprofiled 22. While one translator mask 32a creates a pattern of ablation, the other mask 32b is positioned by the translation mechanism 40 so that the circular aperture 38 is aligned with the iris 16. This allows all the light passing through hyperopic-astigmatic aperture 36 of mask 32a to reach iris 16. The same laser ablation procedure is repeated in the orthogonal direction by positioning mask 32a so that its circular aperture 38 is aligned with iris 16 and then translating hyperopic-astigmatic aperture 36 of mask 32b across the emitted radiation. During the second procedure, it may be desirable to adjust the imaging optics 28 to compensate for the displacement of the second mask 32b. FIG. 5 is a schematic diagram of another embodiment of the invention. System 10B includes a masking apparatus 30 containing only one translator mask 32. The mask 32 is linearly translated across the radiation beam by the translation mechanism 40. The mask 32 can be rotated by rotational mechanism 50 once a first pattern of ablation is performed. Hyperopic-astigmatic corrections are performed by (1) rotating rotation mechanism 50 to align mask 32 with the meridian of the cornea that has the steepest radius of curvature; (2) beginning the delivery of laser pulses and translating the parabolic section 34 of aperture 36 across the beam of laser radiation; (3) halting the delivery of laser pulses and rotating mechanism 50 by ninety degrees; (4) reinitiating the delivery of laser pulses and translating parabolic section 34 across the beam of radiation once again.

FIGS. 6A-E show the operation of the hyperopic-astigmatic aperture 36. For clarity, only parabolic portion 34 of aperture 36 is shown. FIG. 6A shows a top view of hyperopic- astigmatic aperture 36 aligned over surface 22. Initially, mask 32 is disposed off-axis relative to surface 22, so that no light passing through mask 32 impacts surface 22. Then mask 32 translates in the direction of anow 39 so portions of the light passing through aperture 34 impact surface 22. Mask 32 continues to translate in the direction of arrow 39 until once again, none of the light passing through aperture 34 impacts surface 22.

FIGS. 6B-E show four "snap shots" of the ablation patterns on surface 22 resulting from the translation of aperture 34 as described above. Aperture 34 prevents any light from impacting surface 22 along center line 19, but ablation has occurred on both sides of line 19. This translation imparts a cylindrical correction to surface 22 (i.e., the radius of curvature of the meridian perpendicular to line 19 has been altered). Translating aperture 34 along the meridian perpendicular to line 19 will perform an independent cylindrical correction (i.e., this will alter the radius of curvature of meridian 19). Thus, by performing the corrections one axis at a time, the cylindrically profiled surface (astigmatic) is transformed to a spherically profiled surface.

FIGS. 7A-C illustrate the use of hyperopic-astigmatic aperture 36 to create a blend zone. FIG. 7 A shows a hyperopic surface 22 to be reprofiled. Translation of hyperopic- astigmatic aperture 36 across iris 16, as described above in connection with FIG. 6, increases the curvature of surface 22 and creates a spherically shaped region 23. However, as shown in FIG. 7B, spherically shaped region 23 has sharp edges 24. Hyperoptic-astigmatic aperture 36 can also be used to smooth edges 24 to create the blend zone 25 shown in FIG. 7C. Blend zone 25 is created by translating hyperopic-astigmatic aperture 36 to align the annular portion 35 with surface 22. Annular portion 35 allows light to fall on surface 22 only in a ring, shown in FIG. 7C as the region between inner lines 26 and outer lines 27. Initially, iris 16 is opened to a diameter smaller than that defined by inner lines 26, so any laser light passed by aperture 35 is blocked by iris 16. Iris 16 is then increasingly dilated to allow light to impact surface 22 between lines 26 and 27 thus allowing ablation of the sharp edges and creation of blend zone 25.

FIG. 8 is a top sectional view of the masking apparatus shown in FIG. 5. Translation mechanism 40 (not shown) can translate mask 32 along axis 95. Mask 32 is shown positioned for a myopic corrective procedure with circular aperture 37 disposed over iris 16 (not shown). Rotational mechanism 50 is a geared ring. Rotation of ring 50 rotates mask 32, axis 95, and the translation mechanism.

Rotation of key 72 drives rotation of ring 50. Key 72 can also be shifted to interlock with gear 99 rather than ring 50. Rotation of gear 99 adjusts the size of the opening of adjustable iris 16. Key 72 is rotated by a rotational motor 84 (shown in FIG. 9) available, for example, from Harmonic Drives Systems, Inc. By use of key 72, one motor can control both the dilation of iris 16 and the rotational alignment of mask 32. Rotation of ring 50 is also be controlled by anti-backlash gear 51.

FIG. 9 presents a detailed cross-sectional, side view of the system shown in FIG. 5. Rotational motor 84 rotates mask 90, and translation motor 46 along with housing 94. Rotation sensor 86 monitors the angular position of mask stage 90. Rotational motor 84 also controls the dilation of iris 16 via key 72 as described in connection with FIG. 8. Motor 70 shifts key 72 thereby controlling whether rotational motor 84 turns housing 94 or adjusts iris 16. Iris position sensor 74 monitors the dilation of iris 16. Mask position sensor 88 monitors the position of stage 90 making it possible to align any of the apertures of mask 32 (not shown) with iris 16.

FIG. 10 is a three-dimensional graph by computer stimulation of a sphero-hyperopic correction performed by a system in accordance with the invention. The axes 100 and 101, which form a plane orthogonal to the direction of the laser beam performing the ablation, define in millimeters the x-, y- coordinates of the optical zone of the eye. The axis 102, which is orthogonal to the plane defined by the axes 100 and 101, defines in micrometers the z- coordinate corresponding to the depth of a cut produced by the radiation source. As illustrated in this graph, the depth of the cut represented on the axis 102 can vary from 0 to 6.5 microns over the area bounded by the axes 100 and 101.

Claims

C aims

1. An apparatus for reprofiling a surface by ablation, the apparatus being adapted for positioning between a beam of ablative radiation and a target surface to vary an exposure area of the surface to which the radiation is delivered, comprising: masking means for masking the beam of radiation, the masking means having an aperture of predefined shape to selectively pass a portion of the radiation; and drive means for moving the aperture of the masking means across the beam of radiation in two different directions to effect a first pattern and a second pattern of ablation at the surface, whereby the cumulative effect of the first and second pattern is selective ablation and reshaping of the surface.

2. The apparatus of claim 1 wherein the drive means further comprises translation means for moving the aperture of the masking means across the beam along a first path to effect the first pattern of ablation; and rotation means for rotating the masking means relative to the surface to permit the translation means to move the aperture across the beam along a second orthogonal path to effect the second pattern of ablation at the surface.

3. The apparatus of claim 1 wherein the masking means comprises a first and second mask each having an aperture of predefined shape, and wherein the drive means comprises a first and second translation means, the first translation means for moving the first mask across the beam along an axis to effect the first pattern of ablation, and the second translation means for moving the second mask, perpendicular to the axis, across the beam to effect the second pattern of ablation.

4. The apparatus of claim 1 wherein the aperture has an hour glass shape.

5. The apparatus of claim 1 wherein the apparatus further comprises rate control means for controlling the speed at which the aperture is moved across the beam of radiation.

6. The apparatus of claim 1 wherein the apparatus further comprises imaging means for imaging the apertureof the masking means onto the surface.

7. The apparatus of claim 1 wherein the apparatus further comprises projection means for projecting the beam onto the surface following passage through the aperture of the masking means.

8. The apparatus of claim 1 wherein the apparatus further comprises an adjustable iris for varying the width of the beam.

9. The apparatus of claim 1 wherein the masking means has a portion having hour glass shape and a portion having an annular shape.

10. The apparatus of claim 9 wherein the masking means further includes a second aperture having a circular shape.

11. A method of reprofiling a surface by ablation employing a beam of ablative radiation emitted comprising: disposing a mask within the beam of radiation, the mask having an aperture of predefined shape to selectively pass a portion of the radiation; and moving the aperture of the masking means across the beam of radiation in two different directions to effect a first pattern and a second pattern of ablation at the surface, whereby the cumulative effect of the first and second pattern is selective ablation and reshaping of the surface.

12. The method of claim 1 1 wherein the method further comprises moving the aperture of the mask across the beam along a first path to effect the first pattern of ablation; and rotating the mask relative to the surface to permit the translation means to move the aperture across the beam along a second orthogonal path to effect the second pattern of ablation at the surface.

13. The method of claim 1 1 wherein the mask comprises a first and second mask element, each having an aperture of predefined shape, and wherein the step of moving the aperture of the mask further comprises moving the first mask element across the beam along a first path to effect the first pattern of ablation, and also moving the second mask element along a different path across the beam to effect the second pattern of ablation.

14. The method of claim 11 wherein the method further comprises moving said mask at different speeds along the different directions.

15. The method of claim 1 1 wherein the method further comprises imaging the aperture onto the surface.

16. The method of claim 1 1 wherein the method further comprises projecting the beam which passes through the aperture onto the surface.

17. The method of claim 1 1 wherein the method further comprises varying the width of the beam.

18. The method of claim 11 wherein the method further comprises forming a blend zone in a peripheral region of the ablated surface.

19. A system for reprofiling a surface by ablation including a source of ablative radiation, a mask, disposed between the source and the surface, defining first, second, and third apertures, the first aperture having a portion that has an hour glass shape, and a portion that has an annular shape, the second aperture having a circular shape, and the third aperture having a rectangular shape, adjustable iris means disposed between the source and the surface, translation means for translating the mask along an axis for aligning the surface and the iris with any of the first, second or third apertures, and for translating the hour glass shaped portion of the first aperture across the beam of radiation, and rotation means for rotating the axis in a plane substantially normal to the beam of radiation.

20. The system of claim 19 wherein the translation means further comprises rate control means for controlling the speed at which the mask is translated.