Femtosecond laser system and methods for photorefractive keratectomy
Embodiments of this invention generally relate to ophthalmic laser procedures and, more particularly, to systems and methods for lenticular laser incision. In an embodiment, an ophthalmic surgical laser system comprises a laser delivery system for delivering a pulsed laser beam to a target in a subject's eye, an XY-scan device to deflect the pulsed laser beam, a Z-scan device to modify a depth of a focus of the pulsed laser beam, and a controller configured to form a top lenticular incision and a bottom lenticular incision of a lens in the subject's eye, or just a bottom lenticular incision.
1. A laser based ophthalmic surgical system for performing a photorefractive keratectomy procedure in an eye of a patient, the system comprising:
a laser configured to generate femtosecond pulsed laser beam;
an XY-stage and a Z-stage configured to deflect the to deflect the pulsed laser beam; and
a controller configured to:
control the laser to generate a femtosecond laser pulse; and
control the XY-stage and Z-stage to deflect the laser beam in an incision scanning pattern, the incision scanning pattern including an epithelial incision portion that transects an epithelium layer of a cornea of the eye and a stromal incision portion located in a stromal layer of the cornea so as to form a lenticule which is defined by an anterior surface of the cornea and the incision scanning pattern in the epithelium layer and the stromal layer and which is separated from underlying and surrounding portions of the cornea,
wherein the epithelial incision portion either extends in a depth direction between an upper surface of the stromal layer and the anterior surface of the cornea, or extends inwardly towards a center of the epithelial incision portion in a direction from the upper surface of the stromal layer to the anterior surface of the cornea, wherein the stromal incision portion is curved, and wherein the stromal incision portion and the epithelial incision portion intersect at an angle relative to each other,
wherein the lenticule comprises both a stromal portion shaped to affect a refractive property of the eye of the patient and an epithelial portion overlaying the stromal portion, wherein both top and bottom surfaces of the epithelial portion have sizes equal to or smaller than a size of an upper surface of the stromal portion, the stromal portion having a non-uniform thickness, wherein both the stromal portion and the epithelial portion of the lenticule are separated from the underlying and surrounding portions of the cornea.
2. The ophthalmic surgical laser system of claim 1 further comprising a resonant scanner.
3. The ophthalmic surgical laser system of claim 1 , wherein the XY-scan device deflects the pulsed laser beam to form a scan line.
4. The ophthalmic surgical laser system of claim 3 , wherein the scan line is tangential to the parallels of latitude of the cornea.
5. The ophthalmic surgical laser system of claim 4 , wherein the scan line is moved along the meridians of longitude of the cornea.
6. The ophthalmic surgical laser system of claim 4 , wherein there is a deviation between an end point of the scan line and a point on the spherical surface of the lens.
7. The ophthalmic surgical laser system of claim 1 , wherein the incision scanning pattern is a raster scan.
8. The ophthalmic surgical laser system of claim 1 , wherein the incision scanning patterns is a single raster scan configured to separate both the stromal portion and the overlaying epithelial portion from the underlying portions of the of the eye of the patient.
9. The ophthalmic surgical laser system of claim 1 , wherein the incision scanning pattern is configured such that one can remove both the stromal portion and epithelial portion from the eye with tweezers.
10. The ophthalmic surgical laser system of claim 1 , wherein the incision scanning pattern is configured such that the epithelial portion is connected to the stromal portion.
11. The ophthalmic surgical laser system of claim 1 , wherein the stromal portion of the lenticule has a maximum thickness at its center and decreasing thicknesses at positions located at increasing radial distances from the center.