Compound astigmatic myopia or hyperopia correction by laser ablation

• US 5,997,529 A
• Filed: 10/27/1997
• Issued: 12/07/1999
• Est. Priority Date: 10/28/1996
• Status: Expired due to Fees

• Current Assignee: Lasersight Technologies Inc. (Xianding Weng)
• Original Assignee: Lasersight Technologies Inc. (Xianding Weng)
• Inventors: Han, Xiaofeng, Tang, Fuqian
• Primary Examiner(s): Dvorak, Linda C. M.
• Assistant Examiner(s): GIBSON, ROY DEAN
• Application Number:
  US08/957,608
• Time in Patent Office: 771 Days
• Field of Search: 606/4, 606/5, 606/13, 606/10, 606/9, 219/121.6, 600/300, 600/301, 600/558
• US Class Current: 606/4
• CPC Class Codes: A61F 2009/00872 Cornea
• CPC Class Codes: A61F 2009/00897 Scanning mechanisms or algorithms
• CPC Class Codes: A61F 9/008 using laser
• CPC Class Codes: A61F 9/00804 Refractive treatments

Abstract

An apparatus is provided for performing corneal refractive surgery by ablating a portion of a corneal surface of an eye. The apparatus includes a pulsed laser for producing a pulsed output beam of light. A scanning mechanism scans the output beam, and the output beam is operatively associated with the scanning mechanism such that the output beam may be scanned over a predetermined surface defined by a mathematically derived ablation layer boundary curve for each ablation layer. A controller is operatively associated with the scanning mechanism so as to deliver output beams to the predetermined surface such that center points of output beams may be disposed within the ablation layer boundary curve, on the ablation layer boundary curve, and outside but within a predetermined distance from a nearest point on the ablation layer boundary curve so as to integrate the edges of the ablation layer boundary curve to more closely correspond to the desired ablated shape.

Claims

1. A method of ablating a surface area, comprising:

defining an ablation layer area having a boundary;

defining a plurality of ablation points to ablate a portion of said surface area substantially corresponding to an area defined by said ablation layer area;

providing a scanning mechanism to scan an ablating laser beam across said surface area, said scanning mechanism having a scanning step size;

determining whether a particular one of said plurality of ablation points is within said boundary of said ablation layer area, on said boundary of said ablation layer area, or outside said boundary of said ablation layer area;

scanning said ablating laser beam to move a center of said ablating laser beam to said particular one of said plurality of ablation points to ablate said particular one of said plurality of ablation points if said particular one of said plurality of ablation points is within said boundary of said ablation layer area, or on said boundary of said ablation layer area; and

scanning said ablating laser beam to move a center of said ablating laser beam to said particular one of said plurality of ablation points to ablate said particular one of said plurality of ablation points if said particular one of said plurality of ablation points is outside said boundary of said ablation layer area, and if a distance between said particular one of said plurality of ablation points outside said boundary and said boundary is less than a predetermined distance less than said scanning step size.

2. The method of ablating according to claim 1, wherein:

said surface area is an area of corneal tissue.

3. The method of ablating according to claim 1, further comprising:

setting said predetermined distance to approximately half of said scanning step size.

4. The method of ablating according to claim 1, further comprising:

setting said predetermined distance to be equal to a δ

; and

ablating a particular one of said plurality of ablation points outside said boundary if said particular one of said plurality of ablation points outside said boundary satisfies at least one of following expressions;

space="preserve" listing-type="equation">nΔ

+F(p+δ

,q+δ

)-c≦

0,

space="preserve" listing-type="equation">nΔ

+F(p+δ

,q-δ

)-c≦

0,

space="preserve" listing-type="equation">nΔ

+F(p-δ

,q+δ

)-c≦

0,

space="preserve" listing-type="equation">nΔ

+F(p-δ

,q-δ

)-c≦

0,

where nΔ

is a change in thickness of an nth layer of the corneal surface to be ablated, where F(p,q)=-Z_g1 (x(p,q), y(p,q))+Z_g2 (x(p,q),y(p,q)), where Z_g1 and Z_g2 define final and initial corneal surfaces, respectively, and where c is a constants.

5. The method of ablating according to claim 4, further comprising:

setting said δ

to be equal to δ

approximately half of said scanning step size.

6. The method of ablating according to claim 1, further comprising:

ablating a particular one of said plurality of ablation points outside said boundary if said particular one of said plurality of ablation points outside said boundary satisfies nΔ

+F(p,q)-c≦

0, where nΔ

is a change in thickness of an nth layer of the corneal surface to be ablated, where F(p,q)=-Z_g1 (x(p,q), y(p,q))+Z_g2 (x(p,q),y(p,q)), where Z_g1 and Z_g2 define final and initial corneal surfaces, respectively, where c is a constant, where said scanning mechanism performs a scan along a p-axis of said curve and a q-axis that is orthogonal to the p-axis, and where x and y represent x and y axis, respectively.

7. A method of ablating a surface area, comprising:

providing a scanning mechanism to scan an ablating laser beam across said surface area, said scanning mechanism having a scanning step size;

defining an ablation layer area having a boundary;

defining a plurality of first ablation points within said boundary of said ablation layer area, or on said boundary of said ablation layer area;

providing an integrating algorithm, said integrating algorithm defining a plurality of second ablation points that are outside said boundary of said ablation layer area, and are less than a predetermined distance less than said scanning step size apart from said boundary of said ablation layer area;

scanning said ablating laser beam to move a center of said ablating laser beam to each of said plurality of first ablation points and each of said plurality of second ablation points; and

ablating each of said plurality of first ablation points and each of said plurality of second ablation points.

8. The method of ablating according to claim 7, further comprising:

setting said predetermined distance to approximately half of said scanning step size.

9. The method of ablating a surface area according to claim 7, wherein:

said step of providing an integrating algorithm comprises;

providing an algorithm that determines whether to include an ablation point outside said boundary in said plurality of second ablation points by determining if said ablation point outside said boundary satisfies at least one of following expressions;

space="preserve" listing-type="equation">nΔ

+F(p+,q+δ

)-c≦

0,

space="preserve" listing-type="equation">nΔ

+F(p+,q-δ

)-c≦

0,

space="preserve" listing-type="equation">nΔ

+F(p-,q+δ

)-c≦

0,

space="preserve" listing-type="equation">nΔ

+F(p-,q-δ

)-c≦

0,

where nΔ

is a change in thickness of an nth layer of the corneal surface to be ablated, where F(p,q)=-Z_g1 (x(p,q), y(p,q))+Z_g2 (x(p,q),y(p,q)), where Z_g1 and Z_g2 define final and initial corneal surfaces, respectively, and where c and δ

are constants.

10. The method of ablating according to claim 9, further comprising:

setting said δ

to be equal to δ

approximately half of said scanning step size.

11. The method of ablating according to claim 7, further comprising:

ablating a particular one of said plurality of ablation points outside said boundary if said particular one of said plurality of ablation points outside said boundary satisfies nΔ

+F(p,q)-c≦

0, where nΔ

is a change in thickness of an nth layer of the corneal surface to be ablated, where F(p,q)=-Z_g1 (x(p,q), y(p,q))+Z_g2 (x(p,q),y(p,q)), where Z_g1 and Z_g2 define final and initial corneal surfaces, respectively, where c is a constant, where said scanning mechanism perforrms a scan along a p-axis of said curve and a q-axis that is orthogonal to the p-axis, and where x and y represent x and y axis, respectively.

12. A method of ablating a portion of a surface area using an ablating laser beam scanned across said surface area using a scanning mechanism having a scanning step size, said portion of a surface area being substantially defined by an ablation layer area having a boundary, said portion of said surface area including a plurality of ablation points, said method comprising:

determining whether a particular one of said plurality of ablation points is within said boundary of said ablation layer area, on said boundary of said ablation layer area, or outside said boundary of said ablation layer area;

scanning said ablating laser beam to move a center of said ablating laser beam to said particular one of said plurality of ablation points to ablate said particular one of said plurality of ablation points if said particular one of said plurality of ablation points is within said boundary of said ablation layer area, or on said boundary of said ablation layer area; and

scanning said ablating laser beam to move a center of said ablating laser beam to said particular one of said plurality of ablation points to ablate said particular one of said plurality of ablation points if said particular one of said plurality of ablation points is outside said boundary of said ablation layer area, and if a distance between said particular one of said plurality of ablation points outside said boundary and said boundary is less than a predetermined distance less than said scanning step size.

13. The method of ablating according to claim 12, further comprising:

setting said predetermined distance to approximately half of said scanning step size.

14. The method of ablating according to claim 12, further comprising:

setting said predetermined distance to be equal to a δ

; and

ablating a particular one of said plurality of ablation points outside said boundary if said particular one of said plurality of ablation points outside said boundary satisfies at least one of following expressions;

space="preserve" listing-type="equation">nΔ

+F(p+δ

,q+δ

)-c≦

0,

space="preserve" listing-type="equation">nΔ

+F(p+δ

,q-δ

)-c≦

0,

space="preserve" listing-type="equation">nΔ

+F(p-δ

,q+δ

)-c≦

0,

space="preserve" listing-type="equation">nΔ

+F(p-δ

,q-δ

)-c≦

0,

where nΔ

is a change in thickness of an nth layer of the corneal surface to be ablated, where F(p,q)=-Z_g1 (x(p,q), y(p,q))+Z_g2 (x(p,q),y(p,q)), where Z_g1 and Z_g2 define final and initial corneal surfaces, respectively, and where c is a constants.

15. The method of ablating according to claim 14, further comprising:

setting said a to be equal to approximately half of said scanning step size.

16. The method of ablating according to claim 12, further comprising:

ablating a particular one of said plurality of ablation points outside said boundary if said particular one of said plurality of ablation points outside said boundary satisfies nΔ

+F(p,q)-c≦

0, where nΔ

is a change in thickness of an nth layer of the corneal surface to be ablated, where F(p,q)=-Z_g1 (x(p,q), y(p,q))+Z_g2 (x(p,q),y(p,q)), where Z_g1 and Z_g2 define final and initial corneal surfaces, respectively, where c is a constant, where said scanning mechanism performs a scan along a p-axis of said curve and a q-axis that is orthogonal to the p-axis, and where x and y represent x and y axis, respectively.

17. The method of ablating according to claim 12, wherein:

said surface area is an area of corneal tissue.

18. A method of determining a plurality of ablation points for ablating a portion of a layer of a surface area to substantially achieve a desired post ablation profile of said portion of said layer of said surface area, comprising:

determining an ideal ablation layer area having a boundary, said ideal ablation layer area defining an area corresponding to said desired post ablation profile of said surface area portion of said layer of said surface area;

determining a plurality of first ablation points within said boundary, said plurality of first ablation points having a plurality of first outermost ablation points with respect to a symmetrical center of said ideal ablation layer, said plurality of first outermost ablation points defining a first actual ablation layer area that is smaller than said ideal ablation layer area;

determining a plurality of second ablation points, each of said plurality of second ablation points being disposed outside of said boundary;

determining an integrated sum of said first plurality of ablation points and said second plurality of ablation points, said integrated sum having a plurality of second outermost ablation points with respect to said symmetrical center of said ideal ablation layer, said plurality of second outermost ablation points defining a second actual ablation layer area that more closely matches said ideal ablation layer area than said first actual ablation layer area.

19. The method of determining a plurality of ablation points according to claim 18, wherein:

said step of determining said plurality of second ablation points comprises;

including an ablation point outside said boundary in said plurality of second ablation points if said ablation point outside said boundary satisfies at least one of following expressions;

space="preserve" listing-type="equation">nΔ

+F(p+δ

,q+δ

)-c≦

0,

space="preserve" listing-type="equation">nΔ

+F(p+δ

,q-δ

)-c≦

0,

space="preserve" listing-type="equation">nΔ

+F(p-δ

,q+δ

)-c≦

0,

space="preserve" listing-type="equation">nΔ

+F(p-δ

,q-δ

)-c≦

0,

where nΔ

is a change in thickness of an nth layer of the corneal surface to be ablated, where F(p,q)=-Z_g1 (x(p,q), y(p,q))+Z_g2 (x(p,q),y(p,q)), where Z_g1 and Z_g2 define final and initial corneal surfaces, respectively, and where c and gare constants.

20. The method of determining a plurality of ablation points according to claim 19, further comprising:

setting said δ

to be equal to approximately half of said scanning step size.

21. The method of determining a plurality of ablation points according to claim 18, wherein:

said step of determining said plurality of second ablation points comprises;

including an ablation point outside said boundary in said plurality of second ablation points if said ablation point outside said boundary satisfies nΔ

+F(p,q)-c≦

0, where nΔ

is a change in thickness of an nth layer of the corneal surface to be ablated, where F(p,q)=-Z_g1 (x(p,q), y(p,q))+Z_g2 (x(p,q),y(p,q)), where Z_g1 and Z_g2 define final and initial corneal surfaces, respectively, where c is a constant, where said scanning mechanism performs a scan along a p-axis of said curve and a q-axis that is orthogonal to the p-axis, and where x and y represent x and y axis, respectively.

22. The method of determining a plurality of ablation points according to claim 18, wherein:

said step of determining said plurality of second ablation points comprises;

providing an integration algorithm, said integration algorithm adapted to include an ablation point outside said boundary in said plurality of second ablation points if said ablation point outside said boundary are within a predetermined distance from said boundary.

23. The method of determining a plurality of ablation points according to claim 22, further comprising:

providing a scanning mechanism to scan an ablating laser beam across said surface area, said scanning mechanism having a scanning step size.

24. The method of determining a plurality of ablation points according to claim 23, wherein:

said predetermined distance is approximately half of said scanning step size.

25. The method of determining a plurality of ablation points according to claim 18, wherein:

said surface area is an area of corneal tissue.

26. The method of determining a plurality of ablation points according to claim 23, wherein:

said step of providing said scanning mechanism comprises;

providing a scanning mechanism that scans a circular pattern of concentric output beam spots, wherein a center of said circular pattern is placed randomly on said portion of said layer of said surface area.

27. The method of determining a plurality of ablation points according to claim 23, wherein:

said step of providing said scanning mechanism comprises;

providing said scanning mechanism that scans a linear pattern of output beam spots, wherein a starting point of each line of said liner pattern is randomly selected.

28. An apparatus for scanning an ablating laser beam across a surface area to ablate said surface area to substantially achieve a desired post ablation profile of said surface area, said desired post ablation profile of said surface area being defined by an ideal ablation area having a boundary, said ideal ablation area being approximated by a first actual ablation area that is smaller than said ideal ablation area, said first actual ablation area being defined by a plurality of first outermost ablation points, said plurality of first outermost ablation points being outermost ones of a plurality of first ablation points with respect to a symmetrical center of said ideal ablation area, each of said plurality of first ablation points being disposed within or on said boundary, said apparatus comprising:

a controller adapted to produce a scanner control signal in accordance with a scanning pattern;

a scanning mechanism adapted to move said laser beam across an ablation layer are of said surface area in response to said scanner control signal received from said controller; and

an integrating algorithm adapted to produce said scanning pattern that comprises an integrated sum of said first plurality of ablation points and a plurality of second ablation points, each of said plurality of second ablation points being disposed outside of said boundary, a plurality of second outermost ablation points defining a second actual ablation area, said plurality of second outermost ablation points being outermost ones of said plurality of second ablation with respect to said symmetrical center of said ideal ablation area, said second actual ablation area matching said ideal ablation area more closely than said first actual ablation area.

29. The apparatus for scanning an ablating laser beam across a surface area according to claim 28, wherein:

said integrating algorithm is adapted to include an ablation point outside said boundary in said plurality of second ablation points if said ablation point outside said boundary satisfies at least one of following expressions;

space="preserve" listing-type="equation">nΔ

+F(p+δ

,q+δ

)-c≦

0,

space="preserve" listing-type="equation">nΔ

+F(p+δ

,q-δ

)-c≦

0,

space="preserve" listing-type="equation">nΔ

+F(p-δ

,q+δ

)-c≦

0,

space="preserve" listing-type="equation">nΔ

+F(p-δ

,q-δ

)-c≦

0,

where nΔ

is a change in thickness of an nth layer of the comeal surface to be ablated, where F(p,q)=-Z_g1 (x(p,q), y(p,q))+Z_g2 (x(p,q),y(p,q)), where Z_g1 and Z_g2 define final and initial corneal surfaces, respectively, and where c and rare constants.

30. The apparatus for scanning an ablating laser beam across a surface area according to claim 29, wherein:

said scanning mechanism has a scanning step size.

31. The apparatus for scanning an ablating laser beam across a surface area according to claim 30, wherein:

said δ

to be equal to approximately half of said scanning step size.

32. The apparatus for scanning an ablating laser beam across a surface area according to claim 28, wherein:

said integrating algorithm is adapted to include an ablation point outside said boundary in said plurality of second ablation points if said said ablation point outside said boundary are within a predetermined distance from said boundary.

33. The apparatus for scanning an ablating laser beam across a surface area according to claim 32, wherein:

said scanning mechanism has a scanning step size.

34. The apparatus for scanning an ablating laser beam across a surface area according to claim 33, wherein:

said predetermined distance is approximately half of said scanning step size.

35. The apparatus for scanning an ablating laser beam across a surface area according to claim 28, wherein:

said surface area is an area of corneal tissue.

36. The apparatus for scanning an ablating laser beam across a surface area according to claim 28, wherein:

said integrating algorithm is adapted to include an ablation point outside said boundary in said plurality of second ablation points if said ablation point outside said boundary satisfies nΔ

+F(p,q)-c≦

0, where nΔ

is a change in thickness of an nth layer of the corneal surface to be ablated, where F(p,q)=-Z_g1 (x(p,q), y(p,q))+Z_g2 (x(p,q),y(p,q)), where Z_g1 and Z_g2 define final and initial corneal surfaces, respectively, where c is a constant, where said scanning mechanism performs a scan along a p-axis of said curve and a q-axis that is orthogonal to the p-axis, and where x and y represent x and y axis, respectively.

37. The apparatus for scanning an ablating laser beam across a surface area according to claim 28, further comprising:

a pulsed laser.

38. The apparatus for scanning an ablating laser beam across a surface area according to claim 37, wherein:

said pulsed laser is a UV pulsed laser having an energy level less than 10 mJ/pulse.

39. The apparatus for scanning an ablating laser beam across a surface area according to claim 37, wherein:

said pulsed laser has an output wavelength between 193 and 220 nanometers.

40. The apparatus for scanning an ablating laser beam across a surface area according to claim 28, wherein:

said scanning mechanism is adapted and arranged to scan a circular pattern of concentric circles with a center of said circles being non-co-axial with said symmetrical center of said ideal ablation area.

41. The apparatus for scanning an ablating laser beam across a surface area according to claim 28, wherein:

said scanning mechanism is constructed and arranged to scan a linear pattern of parallel lines of ablation points, wherein a starting point of each parallel line of ablation points is randomly selected with respect to a distance from said boundary of said ideal ablation area.

42. An apparatus for scanning an ablating laser beam across a portion of a surface area defined by an ablation area having a boundary, comprising:

a controller to produce a scan control signal in accordance with an integrated sum of a plurality of ablation points;

a scanning mechanism adapted to move said laser beam across an ablation layer area of said surface area in response to said scan control signal received from said controller, said scanning mechanism having a scanning step size; and

a memory having an integrating algorithm to produce said integrated sum of said plurality of ablation points that includes ones of said plurality of ablation points within or on said boundary, said integrated sum of said plurality of ablation points further including ones of said plurality of ablation points outside said boundary if said ones of plurality of ablation points outside said boundary are within a predetermined distance that is less than said scanning step size from said boundary.

43. The apparatus for scanning an ablating laser beam according to claim 42, wherein:

said predetermined distance is approximately half of said scanning step size.

44. The apparatus for scanning an ablating laser beam according to claim 42, wherein:

said surface area is an area of corneal tissue.

45. The apparatus for scanning an ablating laser beam according to claim 42, wherein:

said integrating algorithm comprises;

an algorithm to include an ablation point outside said boundary in said plurality of second ablation points if said ablation point outside said boundary satisfies at least one of following expressions;

space="preserve" listing-type="equation">nΔ

+F(p+δ

,q+δ

)-c≦

0,

space="preserve" listing-type="equation">nΔ

+F(p+δ

,q-δ

)-c≦

0,

space="preserve" listing-type="equation">nΔ

+F(p-δ

,q+δ

)-c≦

0,

space="preserve" listing-type="equation">nΔ

+F(p-δ

,q-δ

)-c≦

0,

where nΔ

is a change in thickness of an nth layer of the corneal surface to be ablated, where F(p,q)=-Z_g1 (x(p,q), y(p,q))+Z_g2 (x(p,q),y(p,q)), where Z_g1 and Z_g2 define final and initial corneal surfaces, respectively, and where c and δ

are constants.

46. The apparatus for scanning an ablating laser beam according to claim 45, wherein:

said δ

to be equal to approximately half of said scanning step size.

47. The apparatus for scanning an ablating laser beam according to claim 42, wherein:

said integrating algorithm is adapted to include an ablation point outside said boundary in said plurality of second ablation points if said ablation point outside said boundary satisfies nΔ

+F(p,q)-c≦

0, where nΔ

is a change in thickness of an nth layer of the corneal surface to be ablated, where F(p,q)=-Z_g1 (x(p,q), y(p,q))+Z_g2 (x(p,q),y(p,q)), where Z_g1 and Z_g2 define final and initial corneal surfaces, respectively, where c is a constant, where said scanning mechanism performs a scan along a p-axis of said curve and a q-axis that is orthogonal to the p-axis, and where x and y represent x and y axis, respectively.

48. The apparatus for scanning an ablating laser beam according to claim 42, further comprising:

a pulsed laser.

49. The apparatus for scanning an ablating laser beam according to claim 48, wherein:

said pulsed laser is a UV pulsed laser having an energy level less than 10 mJ/pulse.

50. The apparatus for scanning an ablating laser beam according to claim 48, wherein:

said pulsed laser has an output wavelength between 193 and 220 nanometers.

51. The apparatus for scanning an ablating laser beam across a surface area according to claim 42, wherein:

said scanning mechanism is adapted and arranged to scan a circular pattern of concentric circles with a center of said circles being non-co-axial with a symmetrical center of said ablation area.

52. The apparatus for scanning an ablating laser beam across a surface area according to claim 42, wherein:

said scanning mechanism is adapted and arranged to scan a linear pattern of parallel lines of ablation points, wherein a starting point of each parallel line of ablation points is randomly selected with respect to a distance from said boundary of said ablation area.