System and method for photoablation using multiple focal points with rotating beam splitter
View Patent ↗A system and method for performing ophthalmic surgery requires splitting a laser beam into a pattern having a plurality of focal points. The pattern is then moved along a spiral path according to a predetermined, two-phase protocol. In the first phase, a radial spacing “Δr” between spiral lines, and the velocity of the pattern “rω” are held constant as the radius “r” is decreased from r 1 to r 2 . In the second phase the angular velocity “ω” is held constant and the radial spacing “Δr” is proportionally increased as “r” is further decreased from r 2 to r 3 . Additional LIOB is required both inside r 3 , as r is reduced to zero and, then, along the periphery of the treatment area for a rim cut at r 1 .
1. A system for performing ophthalmic laser surgery which comprises:
a source means for generating a pulsed laser beam;
an optical means for focusing the laser beam into a pattern having a plurality of focal points;
an optical scanner means for moving the pattern of focal points along a spiral path, wherein movement of the pattern relative to a central axis is characterized by a variable angular velocity “ω”, and a variable radius “r”; and
a computer means, connected to the optical scanner means, for controlling the pattern in a first phase wherein a radial spacing “Δr” between spiral lines, and the product “rω”, are held substantially constant as “r” is decreased from a radius r 1 to a radius r 2 , and for controlling the pattern in a second phase wherein “ω” is held constant and the radial spacing “Δr” is proportionally increased as “r” is further decreased from the radius r 2 to a radius r 3 .
2. A system as recited in claim 1 wherein the optical means includes a beam splitter, wherein r 1 is approximately 4.5 millimeters, wherein r 2 is approximately 0.85 millimeters and wherein r 3 is approximately 0.5 millimeters.
3. A system as recited in claim 2 wherein the beam splitter is connected to the computer for synchronized rotation of the beam splitter with the movement of the pattern at the angular velocity ω.
4. A system as recited in claim 2 wherein the beam splitter is a “1 to 3” beam splitter.
5. A system as recited in claim 4 wherein the laser beam has an energy of approximately 4.5 μJ, and the energy at each focal point is approximately 1.5 μJ.
6. A system as recited in claim 5 wherein each focal point in the pattern has a separation from an adjacent focal point of approximately 20 μm.
7. A system as recited in claim 6 wherein each pulse of the pulsed laser beam has a duration less than one picosecond, and wherein a pulse is fired approximately every 25 μsec, and further wherein the pattern is moved through a distance of approximately 30 μm between each pulse.
8. A system as recited in claim 2 wherein the first phase is characterized by changing ω from ω 1 =38 Hz to ω 2 =200 Hz, as r is correspondingly changed from r 1 =approximately 4.5 mm to r 2 =approximately 0.85 mm (r 1 ω 1 =r 2 ω 2 =constant).
9. A system as recited in claim 8 wherein the second phase is characterized by a constant ω (ω 2 =200 Hz), and a proportional change in the radial spacing Δr, from Δr=6 μm at r 2 , to Δr=10 μm at r=r 3 .
10. A system as recited in claim 9 wherein the computer moves the pattern in a third phase characterized by a constant ω (ω=200 Hz) and a constant Δr (Δr=10 μm) as r changes from r=r 3 to r=0.
11. A system as recited in claim 9 wherein the computer moves the pattern in a third phase along a linear path characterized by a plurality of substantially parallel lines when r<r 3 .
12. A system as recited in claim 11 further comprising a clear window, wherein the beam splitter is replaced by the clear window during creation of a rim cut at r 1 =approximately 4.5 mm.
13. A system as recited in claim 9 wherein the rotating beam splitter is removed during the third phase and the laser beam is moved with a single focal point.
14. A system for performing ophthalmic laser surgery which comprises:
a source for generating a pulsed laser beam;
a means for splitting the laser beam into a pattern having a plurality of focal points;
an optical means for moving the pattern along a path in accordance with a predetermined protocol wherein the path is a spiral path and movement of the pattern relative to a central axis is characterized by a variable angular velocity “ω”,and a variable radius “r”; and where in the protocol includes: a first phase wherein a radial spacing “Δr” between spiral lines, and the product “rω”, are held substantially constant as “r” is decreased from a radius r 1 of approximately 4.5 millimeters to a radius r 2 of approximately 0.85 millimeters, and a second phase wherein “ω” is held constant and the radial spacing “Δr” is proportionally increased as “r” is further decreased from the radius r 2 of approximately 0.85 millimeters to a radius r 3 of approximately 0.5 millimeters; and
a computer means for synchronizing a movement of the beam splitting means with the movement of the pattern along a predetermined portion of the path.
15. A system as recited in claim 14 wherein the protocol further includes a third phase characterized by a constant angular velocity ω, and a constant radial spacing Δr, as r changes from r =r 3 to r =0, and a rim cut where r =approximately 4.5 mm.
16. A system as recited in claim 14 wherein the protocol further includes a third phase characterized by movement of the pattern along a linear path having a plurality of substantially parallel lines when r<r 3 , and a rim cut where r=approximately 4.5 mm.
17. A method for performing ophthalmic laser surgery which comprises the steps of:
generating a pulsed laser beam, wherein the laser beam has an energy of approximately 4.5 μJ and each pulse has a duration less than one picosecond, and wherein a pulse is fired approximately every 25 μsec;
splitting each pulse of the laser beam into a pattern having a plurality of focal points, with the energy at each focal point being approximately 1.5 μJ and with each focal point in the pattern having a separation from an adjacent focal point of approximately 20 μm;
moving the pattern of focal points along a spiral path, wherein movement of the pattern relative to a central axis is characterized by a variable angular velocity “ω”, and a variable radius “r”, and wherein the pattern is moved through a distance of approximately 30 μm between each pulse; and
synchronizing the splitting step and the moving step to follow a protocol having a first phase wherein a radial spacing “Δr” between spiral lines, and the product “rω”, are held substantially constant as “r” is decreased from a radius r 1 of approximately 4.5 millimeters to a radius r 2 of approximately 0.85 millimeters, and having a second phase wherein “ω” is held constant and the radial spacing “Δr” is proportionally increased as “r” is further decreased from the radius r 2 of approximately 0.85 millimeters to a radius r 3 of approximately 0.5 millimeters.
18. A method as recited in claim 17 further comprising the step of including a third phase into the protocol wherein the third phase is characterized by a constant angular velocity ω, and a constant radial spacing Δr, as r changes from r=r 3 to r=0, and a rim cut where r=approximately 4.5 mm.
19. A method as recited in claim 17 further comprising the step of including a third phase into the protocol wherein the third phase is characterized by movement of the pattern along a linear path having a plurality of substantially parallel lines when r<r 3 , and a rim cut where r=approximately 4.5 mm.