Method for performing ophthalmic laser surgery

Claims

What is claimed is:

1. The method of using an ultraviolet laser beam to change 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 confining the laser beam to a maximum-area circular section producing a spot which is centered on and equal to the area of the cornea to be subjected to ablation, 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 predetermined maximum ablation depth into the stroma, directing the adjusted beam to the cornea in the context of reflection to define a central circular region within the confined beam, said directing step being by reflection to the anterior surface and for that period of time which will accomplish at least some ablative penetration to the predetermined maximum ablation depth, whereby laser-beam impingement upon the cornea is a circle having an outer diameter determined by the central circular region; and, in the course of said period of time, varying the diameter of said central circular region to thereby vary the outer diameter of the spot at corneal impact, said diameter variation proceeding in a range within said maximum-area circular spot; whereby the cornea is impacted with greatest cumulative ablating penetration per unit area at the central region of the ablated area and with ablative penetration decreasing with increasing radius to the outer portion of the ablated area, whereby a myopia-correcting change in the anterior surface may be effected by volumetric removal of corneal tissue.

2. The method of using an ultraviolet laser beam to effect a hyperopia-correcting change in 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 confining the laser beam to a circular spot which is centered on and at least equal to the area of the cornea to be subjected to hyperopia-correcting ablation, 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 predetermined maximum ablation depth into the stroma, and directing the adjusted beam to the cornea in the context of reflection to define the beam as a circular annulus having at least the outer diameter of said area of the cornea to be subjected to hyperopia-correcting ablation, said directing step being by reflection to the anterior surface and for that period of time which will accomplish at least some ablative penetration to the predetermined maximum ablation depth, while varying the inner diameter of the annulus and thus of the projected spot, said inner-diameter variation proceeding for a range of diameters less than the outer diameter of said area of the cornea to be subjected to hyperopia-correcting ablation; whereby the cornea is impacted with greatest cumulative ablating penetration per unit area at the perimeter of the area of the cornea to be subjected to hyperopia-correcting ablation, and with ablative penetration decreasing with decreasing radius to the central portion of the ablated area, whereby a hyperopia-correcting change in the anterior surface may be effected by volumetric removal of corneal tissue.

3. The method of claim 1 or claim 2, wherein the diameter variation is in the direction of diameter reduction.

4. The method of claim 1 or claim 2, wherein the diameter variation is in the direction of diameter expansion.

5. The method of using an ultraviolet laser beam to change 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 confining the laser beam to a maximum-diameter circular section producing a spot which is centered on and is predetermined to establish the outer perimeter of the area of the cornea to be subjected to ablation, 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 predetermined maximum ablation depth into the stroma, directing the adjusted beam to the anterior surface of the cornea in the context of reflection to define the beam as comprising (a) a first circular annulus having the outer diameter of said spot and a finite inner diameter and (b) a second circular annulus having an outer diameter contiguous to the finite inner diameter of said first annulus, said directing step being by reflection to the anterior surface and for that period of time which will accomplish at least some ablative penetration to the predetermined maximum ablation depth, while varying the outer diameter of both annuli to thereby vary the outer diameter of each of two concentric ablating spots at corneal impact, the variation in outer diameter of said first annulus proceeding in a range of diameters up to the diameter of said spot, and the variation in outer diameter of said second annulus proceeding in the range of diameters up to said finite diameter, whereby a myopia-correcting change in the anterior surface may be effected by volumetric removal of corneal tissue to achieve a Fresnel-type characterization of the anterior surface.

6. The method of using an ultraviolet laser beam to change 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 confining the laser beam to an intermediate-diameter circular section producing a spot which is centered on and effectively expandable to the maximum diameter of the area of the cornea to be subjected to ablation, 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 predetermined maximum ablation depth into the stroma, directing the adjusted beam to the cornea in the context of reflection to define the beam as comprising (a) a first circular annulus having the outer diameter of said spot and a finite inner diameter and (b) a second circular annulus having an outer diameter contiguous to the finite inner diameter of said first annulus, said directing step being by reflection to the anterior surface and for that period of time which will accomplish at least some ablative penetration to the predetermined maximum ablation depth, while varying the inner diameter of both annuli to thereby vary the inner diameter of each of two concentric ablating spots at cornea impact, the variation in inner diameter of said first annulus proceeding in a range of diameters up to the diameter of said spot, and the variation in inner diameter of said second annulus proceeding in a range of diameters up to said finite diameter, whereby a hyperopia-correcting change in the anterior surface may be effected by volumetric removal of corneal tissue to achieve a Fresnel-type characterization of the anterior surface.

7. The method of using an ultraviolet laser beam to correct an astigmatic property 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 confining the laser beam to a maximum-area section producing a spot which is centered on and spans the area of the cornea to be subjected to ablation, 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 predetermined maximum ablation depth into the stroma, directing the adjusted beam to the cornea in the context of reflection to define the spot as a projected rectangle which is centered on and of elongate length which spans said area of the cornea, orienting the elongate length direction as a central longitudinal axis of the projected rectangular spot to accord with the orientation of the cylindrical axis of the astigmatism to be corrected, said directing step being by reflection to the anterior surface and for that period of time which will accomplish at least some ablative penetration to the predetermined maximum ablation depth, and varying the width of the projected rectangular spot, said width variation being symmetrical laterally of the central longitudinal axis and within the span of said maximum-area section, whereby the cornea is impacted with greatest cumulative ablative penetration per unit area along the central longitudinal axis of spot orientation and with ablative penetration decreasing with increasing width to the outer portion of the ablated area, whereby an astigmatism-correcting change in the anterior surface may be effected by volumetric removal of corneal tissue.

8. The method of using a pulsed ultraviolet laser beam to change 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 confining the section of the laser beam to a maximum circular area which is centered on and equal to 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 depth into the stroma, directing a succession of such pulses to the anterior surface of the cornea in the context of reflecting a central circular region of said beam, whereby laser-pulse impingement upon the cornea is a circle having a diameter determined by the reflection, and varying the diameter of said reflection to thereby vary the diameter of laser-pulse impingement upon the cornea, said diameter variation being in a range up to the diameter of said maximum circular-area, whereby the cornea is impacted with the greatest density of pulses per unit area at the central region of the ablated area and with pulse density decreasing with increasing radius to the perimeter of the ablated area, whereby a myopia-correcting change in the anterior surface is effected by volumetric removal of corneal tissue.

9. The method of using a pulsed ultraviolet laser beam to change 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 confining the section of the laser beam to a maximum circular area which is centered on and equal to 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 depth into the stroma, directing a succession of such pulses to the anterior surface of the cornea in the context of reflecting a radially narrow outer circularly annular region of said beam, whereby laser-pulse impingement upon the cornea is a circular annulus having an inner diameter determined by the reflection, and varying the inner diameter of said reflection to thereby vary the inner diameter of laser-pulse impingement upon the cornea, said diameter variation being in a range up to the outer diameter of said outer annular region, whereby the cornea is impacted with greatest density of pulses per unit area at the perimeter of the ablated area and with pulse density decreasing with decreasing radius to the center of the ablated area, whereby a hyperopia-correcting change in the anterior surface is effected by volumetric removal of corneal tissue.

10. The method of using an ultraviolet laser beam to change 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 confining the laser beam to a maximum-area circular spot which is centered on and equal to the area of the cornea to be subjected to ablation, 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 predetermined maximum ablation depth into the stroma, and directing the adjusted beam to the anterior surface of the cornea for that period of time which will accomplish at least some ablative penetration to the predetermined maximum ablation depth, while varying the diameter of the projected spot, said variation proceeding in a range within said maximum-area spot whereby the cornea is impacted with greatest density of laser-beam exposure per unit area at the central region of the ablated area and with density of laser-beam exposure decreasing with increasing radius to the outer portion of the ablated area, whereby a myopia-correcting change in the anterior surface may be effected by volumetric removal of corneal tissue.

11. The method of using an ultraviolet laser beam to effect a hyperopia-correcting change in 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 confining the laser beam to a circular spot which is centered on and of at least the area of the cornea to be subjected to hyperopia-correcting ablation, 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 predetermined maximum ablation depth into the stroma, directing the adjusted beam to the anterior surface of the cornea in the context of masking a central circular region within said circular spot, said directing step being for that period of time which will accomplish at least some ablative penetration to the predetermined maximum ablation depth, whereby laser-beam impingement upon the cornea is a circular annulus having an inner diameter determined by the circular mask; and, in the course of said period of time, varying the diameter of said mask to thereby vary the inner diameter of the circular annulus, said mask-diameter variation proceeding to but short of the diameter of said maximum-area circular spot; whereby the cornea is impacted with greatest cumulative ablating penetration per unit area at the perimeter of the hyperopia-correcting area and with ablative penetration decreasing with decreasing radius to the center of the hyperopia-correcting area.

12. The method of using a pulsed ultraviolet laser beam to effect a hyperopia-correcting change in 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 confining the laser beam to a circular spot which is centered on and of at least the area of the cornea to be subjected to hyperopia-correcting 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, directing a succession of such pulses to the anterior surface of the cornea in the context of masking a central circular region within said circular spot, whereby laser-pulse impingement upon the cornea is a circular annulus having an inner diameter determined by the circular mask, and varying the diameter of the circular mask, said mask-diameter variation being up to the diameter of said hyperopia-correcting area, whereby the cornea is impacted with the greatest density of pulses per unit area at the perimeter of the hyperopia-correcting area and with pulse density decreasing with decreasing radius to the center of the hyperopia-correcting area.

13. The method of using a pulsed ultraviolet laser beam to change 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 confining the laser beam to a maximum-area circular spot which is centered on and equal to 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, and directing a succession of such pulses to the anterior surface of the cornea in a succession of stepped increments of changing radius of circular spots which are concentric with respect to the optical center, said succession being continued over the range up to said maximum area, whereby the cornea is impacted with greatest density of pulses per unit area at the central region of the ablated area and with pulse density decreasing with increasing radius to the outer portion of the ablated area, whereby a myopia-correction change in the anterior surface may be effected by volumetric removal of corneal tissue.

14. The method of claim 10 or claim 11, wherein the diameter variation is in the direction of diameter reduction.

15. The method of claim 10 or claim 11, wherein the diameter variation is in the direction of diameter expansion.

16. The method of claim 11 or claim 12, wherein the laser-beam spot is larger than the area of the cornea to be subjected to hyperopia-correcting ablation, thereby establishing an outer annulus of laser-beam exposure surrounding the hyperopia-correcting annulus, and varying the outer diameter of said outer annulus while effecting the hyperopia-correcting change, said outer-diameter variation commencing at substantially the outer diameter of the area of hyperopia-correcting change and proceeding with outward diameter expansion.

17. The method of claim 10 or claim 11 or claim 13 or claim 12, in which the diameter variation is cumulatively such, in the course of said period of time, as to effect a radial distribution of laser-beam exposure which is quasiparabolic about the sectional center of laser-beam projection.

18. The method of claim 11 or claim 12, in which the laser-beam spot is larger than the area of the cornea to be subjected to hyperopia-correcting ablation, thereby establshing an outer annulus of laser-beam exposure surrounding the hyperopia-correcting annulus while effecting the hyperopia-correcting change, said outer-diameter variation commencing at substantially the outer diameter of said area of hyperopia-correcting change and proceeding with outward diameter expansion, and in which the radial span between inner and outer diameters of said outer annulus is between 5 and 15 percent of the maximum diameter of the area of hyperopia-correcting change.

19. The method of claim 11 or claim 12, in which the laser-beam spot is larger than the area of the cornea to be subjected to hyperopia-correcting ablation, thereby establishing an outer annulus of laser-beam exposure surrounding the hyperopia-correcting annulus while effecting the hyperpia-correcting change, said outer-diameter variation commencing at substantially the outer diameter of said area of hyperopia-correcting change and proceeding with outward diameter expansion, and in which the radial span between inner and outer diameters of said outer annulus is approximately 10 percent of the maximum diameter of the area of hyperopia-correcting change.

20. The method of claim 11 or claim 12, in which the laser-beam spot is larger than the area of the corena to be subjected to hyperopia-correcting ablation, thereby establishing an outer annulus of laser-beam exposure surrounding the hyperopia-correcting annulus while effecting the hyperopia-correcting change, said outer-diameter variation commencing at substantially the outer diameter of said area of hyperopia-correcting change and proceeding with outward diameter expansion, and in which said outer-diameter variation is cumulatively such, in the course of said period of time, as to effect a radial distribution of laser-beam exposure which is substantially linear in said outer annulus.

21. The method of using an ultraviolet laser beam to change 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 confining the laser beam to a maximum-diameter circular spot which is centered on and is predetermined to establish the outer perimeter of the area of the cornea to be subjected to ablation, 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 predetermined maximum ablation depth into the stroma, selecting an opaque circular mask of diameter less than maximum diameter to be subjected to ablation and centering the mask on an optical axis and between the cornea and the laser beam, and directing the adjusted beam to the anterior surface of the cornea for that period of time which will accomplish at least some ablative penetration to the predetermined maximum ablation depth, while reducing the spot diameter from said maximum to the diameter of said circular mask, removing the mask, and directing the adjusted beam to the anterior surface of the cornea while also continuing to reduce the spot diameter within the previously masked area, whereby a hyperopia-correcting change in the anterior surface may be effected by volumetric removal of corneal tissue to achieve a Fresnel-type characterization of the anterior surface.

22. The method of using an ultraviolet laser beam to change 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 confining the laser beam to an intermediate-diameter circular spot which is centered on and expandable to the maximum diameter of the area of the cornea to be subjected to ablation, 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 predetermined maximum ablation depth into the stroma, selecting an opaque circular mask of said intermediate diameter, centering the mask on an optical axis and between the cornea and the laser beam, and varying the expansion of the spot circle of the adjusted laser beam while directing the same to the anterior surface of the cornea for that period of time which will accomplish at least some ablative penetration to the predetermined maximum ablation depth, said expansion being continued to the point of expanded-spot size reaching the full periphery of the area to be subjected to ablation, removing the mask, and directing the adjusted beam to the anterior surface of the cornea in a program of spot-size variation in the range up to said intermediate diameter wherein the preponderance of ablation is near the center of said intermediate-diameter spot, whereby a myopia-correcting change in the anterior surface may be effected by volumetric removal of corneal tissue to achieve a Fresnel-type characterization of the anterior surface.

23. The method of using an ultraviolet laser beam to correct an astigmatic property 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 confining the laser beam to a projected rectangular spot which is centered on and of elongate length which diametrically spans the area of the cornea to be subjected to ablation, 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 predetermined maximum ablation depth into the stroma, orienting the elongate length direction of the projected rectangular spot to accord with the orientation of the cylindrical axis of the astigmatism to be corrected, and directing the adjusted beam to the anterior surface of the cornea for that period of time which will accomplish at least some ablative penetration to the predetermined maximum ablation depth, and varying the width of the projected rectangular spot, said width variation being in the range up to the diametrical span of said area, whereby the cornea is impacted with greatest cumulative ablative penetration per unit area along the diameter of spot orientation and with ablative penetration decreasing with increasing spot width to the outer portion of the ablated area, whereby an astigmatism-correcting change in the anterior surface may be effected by volumetric removal of corneal tissue.

24. 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 in the nature of an elongate line oriented on the corneal diameter which corresponds to the axis of astigmatic error, 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 in terms of the period of time necessary to reduce to substantially zero the cylindrical curvature responsible for the astigmatism, and for said period of time directing the adjusted beam to the anterior surface of the cornea while varying the width of the projected spot, whereby an astigmatism-correcting change may be effected in the anterior surface of the cornea by volumetric removal of corneal tissue, to thereby leave essentially only spherical error to be corrected; then confining the laser beam to a circular spot which is centered on and equal to the maximum area of the cornea to be subjected to myopia-correcting ablation, predetermining a second period of time for accomplishment of at least some further ablative penetration which corresponds to the maximum required for myopia-correction, and for said second period of time directing the circular spot to the anterior surface of the cornea while varying the diameter of the circular spot within the range up to the diameter of said maximum area, whereby a myopia-correcting change in the anterior surface may be effected by further volumetric removal of corneal tissue.

25. 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 in the nature of an elongate line oriented on the corneal diameter which corresponds to the axis of astigmatic error, 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 depth which is but a fraction of a maximum ablation depth, said maximum ablation depth having been predetermined in terms of the period of time necessary to reduce to substantially zero the cylindrical curvature responsible for the astigmatism, and for said period of time directing the adjusted beam to the anterior surface of the cornea while varying the width of the projected spot, whereby an astigmatism-correcting change may be effected in the anterior surface of the cornea by volumetric removal of corneal tissue, to thereby leave essentially only spherical error to be corrected; then confining the laser beam to a circular spot which is centered on and at least equal to the area of the cornea to be subjected to hyperopia-correcting ablation, predetermining a second period of time for accomplishment of at least some further ablative penetration which corresponds to the maximum required for hyperopia correction, selecting an opaque mask providing circular masking at diameters varying up to the diameter of said hyperopia-correcting area, and for said second period of time directing the circular spot to the cornea while varying the circular masking diameter up to substantially the diameter of said hyperopia-correcting area, whereby a hyperopia-correcting change in the anterior surface may be effected by further volumetric removal of corneal tissue.

26. The method of using a pulsed ultraviolet laser beam to change 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 confining the laser beam to a circular spot which is centered on and equal to a predetermined 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, selecting an opaque circular mask of area less than the predetermined area to be subjected to ablation, centering the mask on the optical axis and between the cornea and the laser beam, whereby an annular area is defined for ablation of an elemental Fresnel-characterized surface, and directing a succession of such pulses to the anterior surface of the cornea in a succession of varying outer radius of said annular area, such variation being between the area of the mask and said predetermined area, whereby a first myopia-correcting curvature change in the anterior surface may be effected by a first volumetric removal of corneal tissue within said annular area; removing the mask, and directing another succession of such pulses to the anterior surface of the cornea in a succession of stepped increments of varying circular-spot area which (a) are concentric to the optical center and (b) are within the previously-masked area, whereby a second myopia-correcting curvature change in the anterior surface may be effected by a second volumetric removal of corneal tissue within the previously-masked area.

27. The method of using a pulsed ultraviolet laser beam to change 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 confining the laser beam to a circular spot which is centered on and equal to a predetermined 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; directing a first succession of such pulses to the anterior surface of the cornea in a succession of varying outer radius within a central circle of diameter less than that of said predetermined area, whereby a first myopia-correcting curvature change in the anterior surface may be effected by a first volumetric removal of corneal tissue within said central circle; opaquely masking the central circle; and then directing a second succession of such pulses to the anterior surface of the cornea in a succession of varying outer radius within the annulus defined by presence of the mask within said predetermined area, whereby a second myopia-correcting curvature change in the anterior surface may be effected by a second volumetric removal of corneal tissue within said annulus.

28. The method of using a pulsed ultraviolet laser beam to change 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 confining the laser beam to a circular spot which is centered on and equal to a predetermined 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; opaquely masking the predetermined area with a succession of circles of varying outer diameter in a range between said predetermined area and the area of an intermediate circle of diameter less than that of said predetermined area, and directing a first succession of such pulses to the anterior surface of the cornea in the course of masking with said succession of circles of varying outer diameter, whereby a first hyperopia-correcting curvature change in the anterior surface may be effected by a first volumetric removal of corneal tissue within an annulus defined by the diameter of the predetermined area and by the diameter of said intermediate circle; masking said annulus to prevent further ablation within said annulus; then opaquely masking said intermediate circle with a succession of circles of varying outer diameter in a range within the inner diameter of said annulus, and directing a second succession of such pulses to the anterior surface of the cornea in the course of masking said intermediate circle with a succession of circles of varying outer diameter, whereby a second hyperopia-correcting curvature change in the anterior surface may be effected by a second volumetric removal of corneal tissue within said intermediate circle.

29. The method of using a pulsed ultraviolet laser beam to correct an astigmatic property of an eye by selectively ablating the anterior surface of a cornea with penetration into the stroma to achieve a volumetric removal of corneal tissue, which method comprises focusing the laser beam to a rectangular spot which is centered on and of elongate length which diametrically spans the area of the cornea to be subjectd 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, orienting the elongate length direction of the rectangular spot to accord with the orientation of the cylindrical axis of the astigmatism to be corrected, and directing a succession of such pulses to the anterior surface of the cornea in a succession of stepped increments of varying width of rectangular spots which are symmetrically positioned with respect to the optical center, whereby the cornea is impacted with greatest density of pulses per unit area along the diameter of spot orientation and with pulse density decreasing with increasing spot width to the outer portion of the ablated area, whereby an astigmatism-correcting change in the anterior surface is effected by volumetric removal of corneal tissue.

30. The method of using an ultraviolet laser beam to effect a myopia-correcting change in 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 cornea tissue, which method comprises delivering the laser beam to impact the cornea as a circular spot having a variable radius that is centered on the central axis of the eye, and varying the radius of said spot in the course of at treatment program to achieve such ablative penetration depth and profile as to characterize the anterior surface with the myopia-correcting change.

31. The method of using an ultraviolet laser beam to effect a hyperopia-correcting change in 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 delivering the laser beam to impact the cornea as a circular annulus having a variable inner radius that is centered on the central axis of the eye, and varying the inner radius of said annulus in the course of a treatment program to achieve such ablative penetration depth and profile as to characterize the anterior surface with the hyperopia-corrected change.

32. The method of claim 30 or claim 31, in which said correcting change in optical properties of the eye is effected upon the anterior surface of a donor-cornea inlay after transplanted assembly thereof to a host cornea, the correcting change being to such stroma-penetration depth in the donor inlay as to complete the correcting change with a profile that is continuous and smooth at adjacency of the anterior surfaces of the host and donor-inlay surfaces.

33. The method of claim 30 or claim 31, in which said correcting change in optical properties of the eye is effected upon the anterior surface of a donor-cornea inlay after transplanted assembly thereof to a host cornea, the correcting change being to such stroma-penetration depth in the donor inlay as to complete the correcting change with a profile that is continuous and smooth at adjacency of the anterior surfaces of the host and donor-inlay surfaces, said host cornea having been first prepared for donor-cornea reception by laser-beam delivery using a circular spot of fixed radius to the point of accomplishing ablative penetration to predetermined maximum ablation depth, and said donor-cornea inlay having been first prepared from a donor cornea for such translated assembled by laser-beam delivery to the posterior surface of the donor cornea until achieving at least some ablative penetration into the stroma region of the donor cornea, the extent of the latter ablative penetration being such as to leave unpenetrated donor-cornea thickness which is at least as great as the extent of laser penetration into the host cornea, and assembling the donor inlay in stroma-to-stroma contact with the ablated region of the host cornea.

34. The method of using an ultraviolet laser beam to effect curvature-correcting change in optical propertries 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 delivering the laser beam to impact the cornea with a circular spot maximum area which is greater than the optically used central area of the cornea, causing the beam to impact the cornea within said central area in a treatment program of beam-size variation to produce an optically corrected curvature in said central area, and causing the mean to impact the cornea with beam-size variation in an outer area which is adjacent to said central area such that in the course of the treatment program the corneal profile in said outer area provides a relatively smooth transition from the area of optically corrected curvature to the corneal profile adjacent to but outside said maximum area, whereby to condition the eye for favorable epithelial regrowth over the area of surgery.