Method for ophthalmological surgery

• US 4,665,913 A
• Filed: 06/24/1985
• Issued: 05/19/1987
• Est. Priority Date: 11/17/1983
• Status: Expired due to Term

• Current Assignee: VISX Incorporated
• Original Assignee: LRI Corporation
• Inventors: L'Esperance, Francis A. Jr.
• Primary Examiner(s): Howell, Kyle L.
• Assistant Examiner(s): SHAY, DAVID M
• Application Number:
  US06/748,358
• Time in Patent Office: 694 Days
• Field of Search: 128/303.1, 128/303.14, 128/395, 128/362, 128/396-398
• US Class Current: 606/3
• CPC Class Codes: A61B 2017/306 holding by means of suction
• CPC Class Codes: A61B 2018/20351 Scanning mechanisms
• CPC Class Codes: A61B 2018/20361 with redirecting based on sensed condition, e.g. tissue analysis or tissue movement
• CPC Class Codes: A61F 2009/00872 Cornea
• CPC Class Codes: A61F 2009/00897 Scanning mechanisms or algorithms
• CPC Class Codes: A61F 9/00804 Refractive treatments
• CPC Class Codes: A61F 9/0081 Transplantation
• CPC Class Codes: A61F 9/00817 Beam shaping with masks
• CPC Class Codes: A61F 9/00819 with photoablatable masks
• CPC Class Codes: A61F 9/009 Auxiliary devices making contact with the eyeball and coupling in laser light, e.g. goniolenses apparatus for eye examination A61B3/0008
• CPC Class Codes: B23K 26/08 Devices involving relative movement between laser beam and workpiece
• CPC Class Codes: B23K 26/082 Scanning systems, i.e. devices involving movement of the laser beam relative to the laser head

Abstract

The invention contemplates use of a scanning laser characterized by ultraviolet radiation to achieve controlled ablative photodecomposition of one or more selected regions of a cornea. Irradiated flux density and exposure time are so controlled as to achieve desired depth of the ablation, which is a local sculpturing step, and the scanning action is coordinated to achieve desired ultimate surface change in the cornea. The scanning may be so controlled as to change the front surface of the cornea from a greater to a lesser spherical curvature, or from a lesser to a greater spherical curvature, thus effecting reduction in a myopic or in a hyperopic condition, without resort to a contact or other corrective auxiliary lens technique, in that the cornea becomes the corrective lens. The scanning may also be so controlled as to reduce astigmatism and to perform the precise incisions of a keratotomy. Still further, the scanning may be so controlled as to excise corneal tissue uniformly over a precisely controlled area of the cornea for precision accommodation of a corneal transplant.

Claims

1. The method of changing optical properties of an eye by operating solely upon the anterior surface of the cornea of the eye, which method comprises selective ultraviolet irradiation and attendant ablative photodecomposition of the anterior surface of the cornea in a volumetric removal of corneal tissue and with depth penetration into the stroma and to a predetermined cruvature profile.

2. The method of changing the anterior surface of the cornea of an eye from an initial curvature having defective optical properties to a subsequent curvature having correctively improved optical properties, which method comprises using ultraviolet laser radiation to selectively ablate the anterior surface of the cornea by photodecomposition, with penetration into the stroma and volumetric sculpturing removal of corneal tissue to such penetration depth and profile as to characterize the anterior surface of the cornea with said subsequent curvature.

3. The method of using a scan-deflectable ultraviolet laser beam to correct an astigmatic condition of an eye, by selectively ablating the anterior surface of the cornea with penetration into the stroma to achieve a volumetric removal of corneal tissue, which method comprises focusing the laser beam to an elemental spot size which is but a small fraction of the area of the cornea to be subjected to ablation, and scanning the laser beam over the locally involved area with beam-exposure flux at a level at which resultant corneal-tissue ablation per scan is to an elemental depth which is but a fraction of desired maximum ablation into the stroma region of the cornea, the scanning of said area being in a pattern to impact the cornea with greatest and substantially uniform density of laser-beam exposure per unit area along a central line of symmetry across said area and through the optical center, said pattern being further characterized by laser-beam cumulative exposure density and accompanying volumetric removal decreasing smoothly with increasing lateral offset on both sides of said central line of symmetry, said central line of symmetry being oriented to accord with a pre-ascertained determination of the cylindrical-axis orientation of the astigmatic condition.

4. The method of claim 3, in which said pattern has a limiting circular perimeter which is centered on the optical axis of the eye.

5. The method of claim 3, in which the pattern of scan action is one of scanning successive lapped areas of progressively changing width, distributed symmetrically between opposed parallel sides which are parallel to and at equal and opposite offset from the central line of symmetry.

6. The method of claim 3, in which the laser beam is pulsed.

7. The method of claim 3, in which the laser beam is continuous wave.

8. The method of claim 3, in which the pattern of area scanning is two-axis rectilineal, wherein line scanning in a first-axis component is oriented to accord with said cylindrical-axis orientation, and wherein scan-line depression in a second-axis component is substantially orthogonal to said cylindrical-axis orientation.

9. The method of using an ultraviolet laser beam to change optical properties of an eye having both astigmatic and myopia errors, by selectively ablating the anterior surface of the cornea with penetration into the stroma to achieve a volumetric removal of corneal tissue, which method comprises confining the laser beam to a projected spot which is small compared to the area containing said errors, adjusting the intensity of laser-beam projection to a limited level at which resultant corneal-tissue ablation per unit time is to an ascertained elemental depth which is but a fraction of a maximum ablation depth, said maximum ablation depth having been predetermined as necessary to reduce to substantially zero the cylindrical curvature responsible for the astigmatism, scanning said spot over a plurality of elongated rectangular-area scans which are centered along an elongate line of symmetry oriented on the corneal diameter which corresponds to the axis of astigmatic error, said rectangular-area scans being of varying width on opposite lateral sides of said line of symmetry, whereby an astigmatism-correcting change in the anterior surface may be effected by volumetric removal of corneal tissue to thereby leave essentially only spherical error to be corrected;

then subjecting the laser beam to a series of scans of circular areas centered on and within the maximum area of the cornea to be subjected to myopia-correction ablation, said series being characterized by varying outer radius, whereby a myopia-correcting further change may be effected in the anterior-surface curvature of the cornea by further volumetric removal of corneal tissue.

10. The method of using an ultraviolet laser beam to change optical properties of an eye having both astigmatic and hyperopia errors, by selectively ablating the anterior surface of the cornea with penetration into the stroma to achieve a volumetric removal of corneal tissue, which method comprises confining the laser beam to a projected spot which is small compared to the area containing said errors, adjusting the intensity of laser-beam projection to a limited level at which resultant cornea-tissue ablation per unit time is to an ascertained elemental depty which is but a fraction of a maximum ablation depth, said maximum ablation depth having been predetermined as necessary to reduce to substantially zero the cylindrical curvature responsible for the astigmatism, scanning said spot over a plurality of elongated rectangular-area scans which are centered along an elongate line of symmetry oriented on the cornea diameter which corresponds to the axis of astigmatic error, said rectangular-area scans being of varying width on opposite lateral sides of said line of symmetry, whereby an astigmatism-correcting change in the anterior surface may be effected by volumetric removal of corneal tissue to thereby leave essentially only spherical error to be corrected;

then subjecting the laser beam to a series of scans of circular annuli centered on the corneal area to be subjected to hyperopia-correcting ablation, said series being characterized by constant outer radius equal to that of said corneal area and being further characterized by varying inner radius of the annuli of successive area scans, whereby a hyperopia-correcting further change may be effected int he anterior-surface curvature of the cornea by further volumetric removal of corneal tissue.

11. The method of using an ultraviolet laser beam to change optical properties of an eye having both astigmatic and myopia errors, by selectively ablating the anterior surface of the cornea with penetration into the stroma to achieve a volumetric removal of corneal tissue, which method comprises confining the laser beam to a projected spot which is small compared to the area containing said errors, and scanning the laser beam over said area with beam-exposure flux at a level at which resultant corneal-tissue ablation per scan is to an elemental depth which is but a fraction of desired maximum ablation into the stroma region of the cornea, the scanning of said area being in a pattern to impact the cornea with greatest and substantially uniform density of laser-beam exposure per unit area along a central line of symmetry across said area and through the optical center, said pattern being further characterized by laser-beam exposure density decreasing smoothly with increasing lateral offset on both sides of said centralline of symmetry, said central line of symmetry being oriented to accord with a pre-ascertained determination of the cylindrical-axis orientation of the astigmatic condition, whereby an astigmatism-correcting change in the anterior surface may be effected by volumetric removal of corneal tissue to thereby leave essentially only spherical error to be corrected;

then further scanning the laser beam over said area in a second pattern of myopia-correcting ablation, said second pattern being characterized by circular symmetry about the optical axis of the eye and by cumulative laser-beam exposure density which is greatest at the optical axis and which decreases smoothly to minimum or zero exposure density at maximum diameter of said area, whereby a myopia-correcting further change may be effected in the anterior-surface curvature of the cornea by further volumetric removal of corneal tissue.

12. The method of using an ultraviolet laser beam to change optical properties of an eye having both astigmatic and hyperopia errors, by selectively ablating the anterior surface of the cornea with penetration into the stroma to achieve a volumetric removal of corneal tissue, which method comprises confining the laser beam to a projected spot which is small compared to the area containing said errors, and scannning the laser beam over the locally involved area with beam-exposure flux at a level at which resultant corneal-tissue ablation per scan is to an elemental depth which is but a fraction of desired maximum ablation into the stroma region of the cornea, the scanning of said area being in a first pattern to impact the cornea with greater and substantially uniform density of laser-beam exposure per unit aea along a central line of symmetry across said area and through the optical center, said first pattern being further characterized by cumulative laser-beam exosure density decreasing smoothly with increasing lateral offset on both sides of said central line of symmetry, said central line of symmetry being oriented to accord with a pre-ascertained determination of the cylindrical-axis orientation of the astigmatic condition, whereby an astigmatism-correcting change in the anterior surface may be effected by volumetric removal of corneal tissue to thereby leave essentially only spherical error to be corrected;

then further scanning the laser beam over said area in a second pattern of hyperopia-correcting ablation, said second pattern being characterized by circular symmetry about the optical axis of the eye and by cumulative laser-beam exposure density which is greatest at maximum diameter and which decreases smoothly to minimum or zero exposure density on the optical axis, whereby a hyperopia-correcting further change may be effected in the anterior-surface curvature of the cornea by/ further volumetric removal of corneal tissue.

13. The method of using an ultraviolet laser beam to change optical properties of an eye having both astigmatic and myopia errors, by selectively ablating the anterior surface of the cornea with penetration into the stroma to achieve a volumetric removal of corneal tissue, which method comprises confining the laser beam to a projected spot which is small compared to the area containing said errors, and scanning the laser beam over said area with beam-exposure flux at a level at which resultant corneal-tissue ablation per scan is to an elemental depth which is but a fraction of desired maximum ablation into the stroma region of the cornea, the scanning of said area being in first and second patterns, one of said patterns being to impact the cornea with greatest and substantially uniform density of laser-beam exposure per unit area a central line of symmetry across said area and through the optical center, said one pattern being further characterized by laser-beam exposure density decreasing smoothly with increasing lateral offset on both sides of said central line of symmetry, said central line of symmetry being oriented to accord with a pre-ascertained determination of the cylindrical-axis orientation of the astigmatic condition, whereby an astigmatism-correcting component of change in the anterior surface may be effected by volumetric removal of corneal tissue;

the other of said patterns being characterized by circular symmetry about the optical axis of the eye and by cumulative laser-beam exposure density which is greater at the optical axis and which decreases smoothly to minimum or zero exposure density at maximum diameter of said area, whereby a myopia-correcting further change may be effected in the anterior-surface curvature of the cornea by further olumetric removal of corneal tissue.

14. The method of using an ultraviolet laser beam to change otpical properties of an eye having both astigmatic and hyperopia errors, by selectively ablating the anterior surface of the cornea with penetration into the stroma to achieve a volumetric removal of corneal tissue, which method comprises confining the laser beam to a projected spot which is small compared to the area containing said errors, and scanning the laser beam over the locally involved area with beam-exposure flux at a level at which resultant corneal-tissue albation per scan is to an elemental depth which is but a fraction of desired maximum ablation into the stroma region of the cornea, the scanning of said area being in first and second patterns, one of said patterns being to impact the cornea with greatest and substantially uniform density of laser-beam exposure per unit area along a central line of symmetry across said across and through the optical center, said one pattern being further characterized by cumulative laser-beam exposure density decreasing smoothly with increasing lateral offset on both side of said central line of symmetry, said central line of symmetry being oriented to accord with a pre-acertained determination of the cylindrical-axis orientation of the astigmatic condition, whereby an astigmatism-correcting component of change in the anterior surface may be effected by volumetric removal of corneal tissue;

the other of said patterns being characterized by circular symmetry about the optical axis of the eye and by cumulative laser-beam exposure density which is greatest at maximum diameter and which decreases smoothly to minimum or zero exposure density on the optical axis, whereby a hyperopia-correcting further change may be effected in the anterior-surface curvature of the cornea by further volumetric removal of corneal tissue.

15. The method of using a scan-deflectable pulsed ultraviolet laser beam to selectively ablate the anterior surface of a cornea with penetration into the stroma to achieve a volumetric removal of corneal tissue, which comprises focusing the laser beam to an elemental spot size which is but a small fraction of the area of the cornea to be subjected to ablation, adjusting the beam-exposure flux per pulse to a level at which resultant corneal-tissue ablation per pulse is to an ascertained elemental depth which is but a fraction of desired maximum ablation into the stroma region of the cornea, and scanning said area in a pattern to impact the cornea with greatest density of pulses per unit area at the optical center and with pulse density decreasing smoothly with increasing radius to the perimeter of said area, whereby a myopia-correcting new curvature is imparted to the cornea within said area.

16. The method of using a scan-deflectable pulsed ultraviolet laser beam to selectively ablate the anterior surface of the cornea with penetration into the stroma to achieve a volumetric removal of corneal tissue, which comprises a focusing the laser beam to an elemental spot size which is but a small fraction of the area of the cornea to be subjected to ablation, adjusting the beam-exposure flux per pulse to a level at which resultant corneal-tissue ablation per pulse is to an ascertained elemental depth which is but a fraction of desired maximum ablation into the stroma region of the cornea, and scanning said area in a pattern to impact the cornea with least density of pulses per unit area at the optical center and with pulse density increasing smoothly with increasing radius to the perimeter of said area, whereby hyperopia-correcting new curvature is imparted to the cornea within said area.

17. The method of using a scan-deflectable pulsed ultraviolet laser beam to selectively ablate the anterior surface of a cornea with penetration into the stroma to achieve a volumetric removal of corneal tissue, which comprises focusing the laser beam to an elemental spot size which is but a small fraction of the area of the cornea to be subjected to ablation, adjusting the beam-exposure flux per pulse to a level at which resultant corneal-tissue ablation per pulse is to an ascertained elemental depth which is but a fraction of desired maximum ablation into the stroma region of the cornea, and scanning said area in a succession of stepped increments which are concentric with respect to the optical center, the scanning for each concentric increment being in a pattern to impact the cornea with greatest density of pulses per unit area at the more inner portion of the increment and with pulse density decreasing with increasing radius to the outer portion of the increment, whereby a Fresnel-chatacterized myopia-correcting change is effected in the cornea.

18. The method of using a scan-deflectable pulsed ultraviolet laser beam to selectively ablate the anterior surface of a cornea with penetration into the stroma to achieve volumetric removal of corneal tissue, which comprises focusing the laser beam to an elemental spot size which is but a small fraction of the cornea to be subjected to ablation, adjusting the beam-exposure flux per pulse to a level at which resultant corneal-tissue ablation per pulse is to an ascertained elemental depth which is but a fraction of desired maximum ablation into the stroma region of the cornea, and scanning said area in a succession of stepped incements which are concentric with respect to the optical center, the scanning for each concentric increment being in a pattern to impact the cornea with greatest density of pulses per unit area at the outer portion of the increment and with pulse density decreasing with decreasing radius to the more inner portion of the increment, whereby a Fresnel-characterized hyperopia-correcting change is effected in the cornea.

19. The method of using a scan-deflectable pulsed ultraviolet laser beam to selectively ablate the anterior surface of the cornea in a corneal-transplant operation with penetration into the stroma to achieve a volumetric removal of corneal tissue, which comprises focusing the laser beam to an elemental spot size which is but a small fraction of the area of the cornea to receive the transplant, scanning said area in a pattern to impact the cornea with substantially uniform density of pulses per unit area and to the extent sufficient to ablate into the stroma region to a depth less than the thickness of the transplant, securing the transplant into the ablated region, whereby transplant material protrudes beyond the anterior profile of adjacent surrounding corneal tissue, and scanning the anterior surface area of the transplant in a pattern to impact the same with a distribution of density of pulses per unit area to achieve a desired anterior profile of the transplant which is smoothly continuous with the profile of adjacent unscanned corneal tissue.

20. The method of using a scan-deflectable pulsed ultraviolet laser beam to selectively ablate the anteriorly surface of the cornea to a predetermined maximum depth of penetration into and volumetric removal of tissue from the corneal stroma in preparation for reception of a corneal transplant within a predetermined area of the cornea, which comprises focusing the laser beam to an elemental spot size which is but a small fraction of said area, adjusting the beam-exposure flux per pulse to a level at which resultant corneal-tissue ablation per pulse is to an ascertined elemental depth which is but a fraction of said predetermined maximum depth of ablation into the stroma region of the cornea, successively scanning said area in a pattern which causes the laser beam to impact the cornea within said area with a substantially uniform density of pulses per unit area to the extent of ablating corneal tissue to substantially uniform elemental depth in a first scan of said area, and repeating such scans of said area to ablate successive substantially uniform element increments of depth until achieving said maximum depth.

21. The method of using a scan-deflectable pulsed ultraviolet laser beam to change the optical properties of an eye by selective ablation of the anterior surface of the cornea with penetration into the stroma to achieve a volumetric removal of corneal tissue in order to effect a desired local change in the curvature of the anterior surface, which comprises focusing the laser beam to an elemental spot size which is but a small fraction of the locally involved area of desired change, adjusting the beam-exposure flux per pulse to a level at which resultant corneal-tissue ablation per pulse is to an ascertained elemental depth which is but a fraction of desired maximum depth of ablation into the strome region of the cornea, and scanning the locally involved area in a pattern to impact the cornea with leat density of pulses per unit area in regions requiring least removal of the corneal tissue and with greatest density of pulses per unit area in regions requiring greater removal of corneal tissue until achievement of said desired local change.

29. The method of claim 21 or claim 28, wherein the laser beam is characterized by a wavelength of less than substantially 400 nm.

30. The method of claim 21 or claim 28, wherein scanning is rectilineal, within limits of said locally involved area.

31. The method of claim 21 or claim 28, wherein scanning is over a spiral course of scan comprising rotary sweeps at progressively changing radius, within limits of said locally involved area.

32. The method of claim 21 or claim 28, wherein the scanning step is computer-programmable.

33. The method of claim 21 or claim 28, wherein the scanning is computer-programmable and wherein the programming establishes an angularly distributed plurality of successive radial displacement sweeps of the laser beam, with respect to the optical axis of the cornea.

22. The method of using a scan-deflectable ultraviolet laser beam to selectively ablate the anterior surface of the cornea with penetration into the stroma to achieve a volumetric removal of corneal tissue, whcih comprises focusing the laser beam to an elemental spot size which is but a small fraction of the area of the cornea to be subjected to ablation, and scanning the laser beam over the locally involved area with beam-exposure flux at a level at which resultant corneal-tissue ablation per scan is to an ascertained elemental depth which is but a fraction of desired maximum ablation into the stroma region of the cornea, the scanning of said area being in a pattern to impact the cornea with greatest density of laser-beam exposure per unit area at the optical center and with laser-beam exposure density decreasing smoothly with increasing radius to the perimeter of said area, whereby a myopia-correcting new curvature is imparted to the cornea within said area.

23. Themethod of using a scan-deflectable ultraviolet laser beam to selectively ablate the anterior surface of a cornea with penetration into the stroma to achieve a volumetric removal of corneal tissue, which comprises focusing the laser beam to an elemental spot size which is but a small fraction of the area of the cornea to be subjected to ablation, and scanning the laser beam over the locally involved area with beam-exposure flux at a level at which resultant corneal-tissue ablation per scan is to an ascertained elemental depth which is but a fraction of desired maximum ablation into the stroma region of the cornea, the scanning of said area being in a pattern to impact the cornea with least density of laser-beam exposure per unit area of the optical center and with laser-beam exposure density increasing smoothly with increasing radius to the perimeter of said area, whereby a hyperopia-correcting new curvature is imparted to the cornea within said area.

24. The method of using a scan-deflectable ultraviolet laser beam to selectively ablate the anterior surface of a cornea with penetration into the stroma to achieve a volumetric removal of corneal tissue, which comprises focusing the laser beam to an elemental spot size which is but a small fraction of the area of the cornea to be subjected to ablation, and scanning the laser beam over the locally involved area with beam-exposure flux at a level at which resultant corneal-tissue ablation per scan is to an ascertained elemental depth which is but a fraction of desired maximum albation into the stroma region of the cornea, the scanning of said area being in a succession of stepped increments which are concentric with respect to the optical center, the scanning for each concentric incrment being in a pattern to impact the cornea with greatest density of lser-beam exposure per unit area at the more inner portion of the increment and with laser-beam exposure density decreasing with increasing radius to the outer portion of the increment, whereby a Fresnel-characterized myopia-correcting change is effected in the cornea.

25. The method of using a scan-deflectable ultraviolet laser beam to selectively ablate the anterior surface of a cornea with penetration into the stroma to achieve a volumetric removal of corneal tissue, which comprises focusing the laser beam to an elemental spot size which is but a small fraction of the area of the cornea to be subjected to ablation, and scanning the laser beam over the locally involved area with beam-exposure flux at a level at which resultant corenal-tissue ablation per scan is to an ascertained elemental depth which is but a fraction of desired maximum ablation into the stroma region of the cornea, the scanning of said area being in a succession of stepped increments which are concentric with respect to the optical center, the scanning for each concentric increment being in a pattern to impact the cornea with greatest density of laser-beam exposure per unit area at the outer portion of the increment and with laser-beam-exposure density decreasing with decreasing radius to the more inner portion of the increment, whereby a Fresnel-characterized hyperopia-correcting change is effected in the corena.

26. The method of using a scan-deflectable ultraviolet laser beam to selectively ablate the anterior surface of a cornea in a corneal-transplate operation with penetration into the stroma to achieve a volumetric removal of corneal tissue, which comprises focusing the laaer beam to an elemental spot size which is but a small fraction of the area of the cornea to receive the transplant, scanning said area in a pattern to impact the cornea with substantially uniform density of laser-beam exposure per unit area and to the extent sufficient to ablate into the stroma region to a depth less than the thickness of the transplant, securing the transplant into the ablated region, whereby transplant material protrudes beyond the anterior profile of adjacent surrounding corneal tissue, and scanning the anterior surface area of the transplant in a pattern to impact the same with a distribution of density of laser-beam exposure per unit area to achieve a desired anterior profile of the transplant which is smoothly continuous with the profile of adjacent unscanned corenal tissue.

27. The method of using a scan-deflectable ultraviolet laser beam to selectively ablate the anterior surface of a cornea to a predetermined maximum depth of penetration into and volumetric removal of tissue from the corneal stroma in preparation for reception of a corneal transplant within a predetermined area of the cornea, which comprises focusing the laser beam to an elemental spot size which is but a small fraction of said area, and scanning the laser beam over said area with beam-exposure flux at a level at which resultant corneal-tissue ablation per pulse is to an ascertained elemental depth which is but a fraction of said predetermined maximum depth of ablation into the stroma region of the cornea, the scanning of said area being in a pattern which causes the laser beam to impact the cornea within said area with a substantially uniform density of laser-beam exposure per unit area to the extent of ablating corneal tissue to substantially uniform elemental depth in a first scan of said area, and repeating such scans of said area to ablate successive substantially uniform elemental increments of depth until achieving said maximum depth.

28. The method of using a scan-deflectable ultraviolet laser beam to change the optical properties of an eye by selective ablation of the anterior surface of the cornea with penetration into the stroma to achieve a volumetric removal of corneal tissue in order to effect a desired local change in the curvature of the anterior surface, which comprises focusing the laser beam to an elemental spot size which is but a small fraction of the locally involved area of desired change, and scanning the laser beam over the locally involved aea with beam-exposure flux at a level at which resultant corneal-tissue ablation per scan is to an ascertained elemental depth which is but a fraction of desired maximum depth of ablation into the stroma region of the cornea, the scanning of the locally involved area being in a pattern to impact the cornea with least densiity of laser-beam exposure per unit area in regions requiring least removal of corneal tissue and with greatest density of laser-beam exposure per unit area in regions requiring greatest removal of corneal tissue until achievement of said desired local change.

34. The method of using an ultraviolet laser beam to change the optical properties of an eye by selectively ablating the anterior surface of the cornea with penetration into the stroma to achieve a volumetric removal of corneal tissue, which method comprises adjusting the intensity of laser-beam projection to level at which resultant corneal-tissue ablation per unit time is to an ascertained elemental depth which is but a fraction of a predetermined maximum ablation depth into the stroma of the cornea, ablating a first area of the cornea to said elemental depth, ablating a second area of the cornea to said elemental depth, one of said areas being larger than the other of said areas but in full overlap with said other area, whereby to the extent of area overlap there is greater cumulative ablative penetration into and accompanying volumetric tissue removal from the cornea than in a region in which said one area does not overlap said other area, and successively ablating further and different overlapping areas at increments of elemental depth to generate an otpically changed corneal profile.

35. The method of claim 34, in which said areas are circular and concentric whereby a myopia-reducing optical change is produced.

36. The method of claim 34, in which said areas are concetric circular annuli having identical outer radii, whereby a hyperopia-reducing optical change is produced.

37. The emthod of using an ultraviolet laser to change the optical properties of an eye, which method comprises adjusting the intensity of laser-beam projection to a level at which laser-beam projection onto the anterior surface of the cornea of the eye will result in corneal-tissue ablation per unit time which is but a fraction of a predetermined maximum ablation depth into the stroma of the cornea, and directing the laser beam at the anterior surface of the cornea in a controlled program of circular-area coverage as a function of time to redefine the anterior-surface curvature by volumetric removal of corneal tissue in the course of selective ablative sculpture of the stroma.

38. The emthod of using an ultraviolet laser to change the optical properties of an eye, wherein the spot size of laser-beam projection is of very small area in relation to the optically usable area of the cornea, which method comprises adjusting the intensity of laser-beam projection to a level at which laser-beam projection onto the anterior surface of the cornea of the eye will result in corneal-tissue ablation per unit time which is but a fraction of a predetermined maximum ablation depth into the stroma of the cornea, and controlling laser-beam projection at the anterior surface of the cornea in a program of direction as a function of time to redefine the anterior surface curvature by volumetric removal of corneal tissue in the course of selective ablative sculpture of the stroma.