High speed corneal lenticular incision using a femtosecond laser
An ophthalmic surgical laser system and method for forming a lenticule in a subject's eye using “fast-scan-slow-sweep” scanning scheme. A high frequency scanner forms a fast scan line, which is placed by the XY and Z scanners at a location tangential to a parallel of latitude of the surface of the lenticule. The XY and Z scanners then move the scan line in a slow sweep trajectory along a meridian of longitude of the surface of the lenticule in one sweep. Multiple sweeps are performed along different meridians to form the entire lenticule surface, and a prism is used to change the orientation of the scan line of the high frequency scanner between successive sweeps. In each sweep, the sweeping speed along the meridian is variable, being the slowest at the edge of the lenticule and the fastest near the apex.
1. An ophthalmic surgical laser system comprising:
a laser delivery system for delivering a pulsed laser beam to a target in a subject's eye;
a high frequency scanner to scan the pulsed laser beam back and forth at a predefined frequency;
an XY-scanner to deflect the pulsed laser beam, the XY-scanner being separate from the high frequency scanner;
a Z-scanner to modify a depth of a focus of the pulsed laser beam; and
a controller configured to control the high frequency scanner, the XY-scanner and the Z-scanner to successively form a plurality of sweeps which collectively form at least one lenticular incision of a lens in the subject's eye, the lens having a curved surface that defines an apex and a Z axis passing through the apex, wherein each sweep is formed by:
controlling the high frequency scanner to deflect the pulsed laser beam to form a scan line, the scan line being a straight line having a predefined length and being tangential to a parallel of latitude of the lens, the parallel of latitude being a circle on the surface of the lens that is perpendicular to the Z axis and has a defined distance to the apex,
controlling the XY-scanner and the Z-scanner to move the scan line along a meridian of longitude of the lens, the meridian of longitude being a curve that passes through the apex and has a defined angular position around the Z axis, and
controlling the laser delivery system to vary a laser pulse energy during each sweep to use a lower laser pulse energy when the scan line is located within a vicinity of the apex of the lenticule than when the scan line is located at an edge of the lenticule,
wherein the plurality of sweeps are successively formed one after another along the respective meridians of longitude which are different from one another.
2. The ophthalmic surgical laser system of claim 1 , wherein the high frequency scanner is a resonant scanner.
3. The ophthalmic surgical laser system of claim 1 , wherein the predetermined length of the scan lines for all sweeps are equal.
4. The ophthalmic surgical laser system of claim 1 , wherein the predetermined length of the scan line for each sweeps is between 0.9 mm and 1.1 mm, and wherein the high frequency scanner has a scanning frequency between 7 kHz and 9 kHz.
5. The ophthalmic surgical laser system of claim 1 , further comprising a prism disposed to receive scanned pulsed laser beam from the high frequency scanner, and wherein the controller is configured to rotate the prism to rotate an orientation of the scan line.
6. The ophthalmic surgical laser system of claim 1 , wherein the at least one lenticular incision includes a top lenticular incision and a bottom lenticular incision, wherein the curved surface is a top surface of the lens corresponding to the top lenticular incision, the lens further including a bottom surface corresponding to the bottom lenticular incision and defining another apex, and wherein the scan line for each of the sweeps forming the top lenticular incision is moved over the top surface of the lens through the apex of the top surface of the lens, and the scan line for each of the sweeps forming the bottom lenticular incision is moved over the bottom surface of the lens through the other apex of the bottom surface of the lens.
7. The ophthalmic surgical laser system of claim 1 , wherein a deviation exists between an end point of the scan line and a point on the surface of the lens which is a spherical surface, the deviation being
δ
=
R
2
+
L
2
4
-
R
≈
L
2
8
R
where R is a radius of curvature of the spherical surface of the lens, and L is the length of the scan line.
8. The ophthalmic surgical laser system of claim 7 , wherein a depth of a focus of the pulsed laser beam is calculated based on the radius of curvature of the spherical surface of the lens.
9. A method for creating a lenticular incision using an ophthalmic surgical laser system, the method comprising the steps of:
generating a pulsed laser beam;
delivering the pulsed laser beam to a target in a subject's eye;
scanning, by a high frequency scanner, the pulsed laser beam back and forth at a predefined frequency;
deflecting, by an XY-scanner, the pulsed laser beam, the XY-scanner being separate from the high frequency scanner;
modifying, by a Z-scanner, a depth of a focus of the pulsed laser beam; and
controlling, by a controller, the high frequency scanner, the XY-scanner and the Z-scanner to successively form a plurality of sweeps which collectively form at least one lenticular incision of a lens in the subject's eye, the lens having a curved surface that defines an apex and a Z axis passing through the apex, including forming each sweep by:
controlling the high frequency scanner to deflect the pulsed laser beam to form a scan line, the scan line being a straight line having a predefined length and being tangential to a parallel of latitude of the lens, the parallel of latitude being a circle on the surface of the lens that is perpendicular to the Z axis and has a defined distance to the apex,
controlling the XY-scanner and the Z-scanner to move the scan line along a meridian of longitude of the lens, the meridian of longitude being a curve that passes through the apex and has a defined angular position around the Z axis, and
controlling the laser delivery system to vary a laser pulse energy during each sweep to use a lower laser pulse energy when the scan line is located within a vicinity of the apex of the lenticule than when the scan line is located at an edge of the lenticule,
wherein the plurality of sweeps are successively formed one after another along the respective meridians of longitude which are different from one another.
10. The method of claim 9 , wherein the predetermined length of the scan lines for all sweeps are equal.
11. The method of claim 9 , wherein the predetermined length of the scan line for each sweeps is between 0.9 mm and 1.1 mm, and wherein the high frequency scanner has a scanning frequency between 7 kHz and 9 kHz.
12. The method of claim 9 , further comprising: controlling, by the controller, a rotation of a prism which is disposed to receive scanned pulsed laser beam from the high frequency scanner to rotate an orientation of the scan line.
13. The method of claim 9 , wherein the at least one lenticular incision includes a top lenticular incision and a bottom lenticular incision, wherein the curved surface is a top surface of the lens corresponding to the top lenticular incision, the lens further including a bottom surface corresponding to the bottom lenticular incision and defining another apex, and wherein the scan line for each of the sweeps forming the top lenticular incision is moved over the top surface of the lens through the apex of the top surface of the lens, and the scan line for each of the sweeps forming the bottom lenticular incision is moved over the bottom surface of the lens through the other apex of the bottom surface of the lens.
14. The method of claim 9 , wherein a deviation exists between an end point of the scan line and a point on the surface of the lens which is a spherical surface, the deviation being
δ
=
R
2
+
L
2
4
-
R
≈
L
2
8
R
where R is a radius of curvature of the spherical surface of the lens, and L is the length of the scan line.
15. The method of claim 14 , wherein a depth of a focus of the pulsed laser beam is calculated based on the radius of curvature of the spherical surface of the lens.