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Managing astigmatic patients

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Managing astigmatic patients

  1. 1. Managing astigmaticpatientsVassilis Kokotas, OptometristClinical Associate OEPF/COVD, U.S.A. Nikos Kozeis, M.D.
  2. 2. Astigmatism LOGO The refractive error of an optical system that creates two principal focal planes instead of a single one.
  3. 3. Astigmatism LOGO When meridians are perpendicular to each other then astigmatism is considered as regular, otherwise is considered irregular.
  4. 4. Corneal astigmatism LOGO Against the rule  Vertical meridian flatter than horizontal.  Corrected with (-) cyl. X 90° With the rule  Vertical meridian steeper than horizontal  Corrected with (-) cyl. X 180°
  5. 5. Astigmatism LOGO Total astigmatic error occurs by integration of corneal and lens astigmatism. Usually, corneal with the rule astigmatism + lenticular against the rule astigmatism.
  6. 6. Incidence of astigmatism among population LOGO 83% of prescriptions incorporate an astigmatic component 15% <0.50 45% 10% 0.50-1.00 60% 1.00-1.50 20% 7% 3% 1.50-2.00 2.00-3.00 >3.00 Hartstein J. - Review of eye terminology
  7. 7. Subjective evaluation of astigmatism LOGO
  8. 8. Subjective evaluation of astigmatism LOGO Fan Chart (or Clock Dial) Test “V” Chart Cross Cylinder Method
  9. 9. Fan Chart (Clock Dial) Test LOGO
  10. 10. Fan Chart (Clock Dial) Test LOGO
  11. 11. Fan Chart (Clock Dial) Test LOGO
  12. 12. Effect of cylindrical error on V.A. LOGO V.A. Uncorrected Uncorrected Spherical Cylindrical Error (DS) Error (DC) 20/20 <0.25 <0.25 20/30 0.50 1.00 20/40 0.75 1.50 20/60 1.00 2.00 20/80 1.50 3.00 20/120 2.00 4.00 20/200 2.00 - 3.00 >5.00 Fogging Lens = Spherical Equivalent of Expected Astigmatism + 0.50
  13. 13. Fan Chart (Clock Dial) Test LOGO
  14. 14. Fan Chart (Clock Dial) Test LOGO (-) cyl. X 90
  15. 15. Fan Chart (Clock Dial) Test LOGO
  16. 16. Fan Chart (Clock Dial) Test LOGO Advantages  No special equipment  Easy to perform for screening  Easy to communicate with high amounts of astigmatism Disadvantages  Difficult discrimination in small amounts of astigmatism  Difficult axis orientation in small amounts of astigmatism  Difficult to communicate in small amounts of astigmatism
  17. 17. “V” Chart LOGO
  18. 18. “V” Chart LOGO
  19. 19. “V” Chart LOGO
  20. 20. “V” Chart LOGO
  21. 21. “V” Chart LOGO Advantages  More accurate than Fan Chart  Easier to communicate than Fan Chart  Easier to check for the right amount of cylinder Disadvantages  Difficult discrimination in small amounts of astigmatism  Difficult axis orientation in small amounts of astigmatism
  22. 22. Cross cylinder optics LOGO +0.50 DC -0.50 DC +/- 0.50 DC
  23. 23. Cross cylinder optics LOGO Plano Plano +/- 0.50 DC
  24. 24. Cross cylinder optics LOGO
  25. 25. Cross cylinder optics LOGO
  26. 26. Determination of axis LOGO -1.0 DS -0.50 DC x 180 1? Cross Cyl. +/- 0.25 DC
  27. 27. Determination of axis LOGO -1.0 DS -0.50 DC x 180 1 2? …or about the same? Cross Cyl. +/- 0.25 DC
  28. 28. Determination of axis LOGO -1.0 DS -0.50 DC x 180 Cross Cyl. +/- 0.25 DC
  29. 29. Determination of axis LOGO -1.0 DS -0.50 DC x 180 Cross Cyl. +/- 0.25 DC
  30. 30. Determination of axis LOGO -1.0 DS -0.50 DC x 165 Cross Cyl. +/- 0.25 DC
  31. 31. Determination of axis LOGO -1.0 DS -0.50 DC x 165 1? Cross Cyl. +/- 0.25 DC
  32. 32. Determination of axis LOGO -1.0 DS -0.50 DC x 165 2 2? …or about the same? Cross Cyl. +/- 0.25 DC
  33. 33. Determination of axis LOGO -1.0 DS -0.50 DC x 165 Cross Cyl. +/- 0.25 DC
  34. 34. Determination of axis LOGO -1.0 DS -0.50 DC x 175 Cross Cyl. +/- 0.25 DC
  35. 35. Determination of axis LOGO -1.0 DS -0.50 DC x 175 1? Cross Cyl. +/- 0.25 DC
  36. 36. Determination of axis LOGO -1.0 DS -0.50 DC x 175 1 2? …or about the same? Cross Cyl. +/- 0.25 DC
  37. 37. Determination of axis LOGO -1.0 DS -0.50 DC x 175 Cross Cyl. +/- 0.25 DC
  38. 38. Determination of axis LOGO -1.0 DS -0.50 DC x 175 Cross Cyl. +/- 0.25 DC
  39. 39. Determination of axis LOGO -1.0 DS -0.50 DC x 170 Cross Cyl. +/- 0.25 DC
  40. 40. Determination of axis LOGO -1.0 DS -0.50 DC x 170 1? Cross Cyl. +/- 0.25 DC
  41. 41. Determination of axis LOGO -1.0 DS -0.50 DC x 170 About the same. 2? …or about the same? Cross Cyl. +/- 0.25 DC
  42. 42. Determination of power LOGO -1.0 DS -0.50 DC x 170 1? Cross Cyl. +/- 0.25 DC
  43. 43. Determination of power LOGO -1.0 DS -0.50 DC x 170 2. 2? …or about the same? Cross Cyl. +/- 0.25 DC
  44. 44. Determination of power LOGO -1.0 DS -0.75 DC x 170 Cross Cyl. +/- 0.25 DC
  45. 45. Determination of power LOGO -1.0 DS -0.75 DC x 170 1? Cross Cyl. +/- 0.25 DC
  46. 46. Determination of power LOGO -1.0 DS -0.75 DC x 170 2. 2? …or about the same? Cross Cyl. +/- 0.25 DC
  47. 47. Determination of power LOGO -1.0 DS -1.00 DC x 170 Cross Cyl. +/- 0.25 DC
  48. 48. Determination of power LOGO -0.75 DS -1.00 DC x 170 Cross Cyl. +/- 0.25 DC
  49. 49. Determination of power LOGO -0.75 DS -1.00 DC x 170 1? Cross Cyl. +/- 0.25 DC
  50. 50. Determination of power LOGO -0.75 DS -1.00 DC x 170 About the same. 2? …or about the same? Cross Cyl. +/- 0.25 DC
  51. 51. Notes on axis LOGO If your endpoint for the determination of axis is alternating between +/- 5°, you can choose an intermediate or lay on the one closer to a major meridian. If changes in axis exceed 90° from your starting point, then consider removing the cylinder and replace it with the spherical equivalent lens.
  52. 52. Notes on power LOGO If your endpoint for the determination of power is alternating between +/- 0.25 DC, keep the lower amount of cylinder. If changes in cylindrical power exceed 0,50 DC then it is suggested that you recheck the axis.
  53. 53. Cross Cylinder LOGO Advantages  Accurate for power and cylinder  Direct effect on perception  Easy to communicate. Comparison Disadvantages  Stability with hand-held cross cylinder  May need more than one power of cross cylinder  Time consuming
  54. 54. Perceptual issues of astigmatism LOGO Astigmatism with the rule creates less visual disability compared to astigmatism against the rule. Xiguana Indians have been great hunters besides of their high uncorrected astigmatic refraction (10% population >3.0 DC). Pensyl CD, et al. 1997 Focused Defocused With the Rule Against the Rule
  55. 55. Perceptual issues of astigmatism LOGO Brain is searching for information that can be useful in dealing with gravity. This means that vertical orientation enriches visual perception. Focused Defocused With the Rule Against the Rule
  56. 56. Effect of cylindrical error and axis on V.A. LOGO V.A. Oblique Against With the Rule the Rule 20/25 0.25 0.50 0.50 20/30 0.75 1.00 1.00 20/40 1.00 1.25 1.50 20/50 1.50 1.75 2.00 20/70 1.75 2.00 2.50 20/100 2.25 2.50 3.00 20/150 2.75 3.00 3.50 20/200 3.50 4.00 4.50
  57. 57. Perceptual issues of astigmatism LOGO
  58. 58. Perceptual issues of astigmatism LOGO Spatial VisualPerception Acuity Motion Color Detection
  59. 59. Perceptual issues of astigmatism LOGO Sensory integration
  60. 60. Perceptual issues of astigmatism LOGO Mismatch
  61. 61. When to prescribe LOGO When patient is symptomatic (reduced acuity, fatigue, photosensitivity, conjuctivity, etc.)  Rarely small (< -0,75 DC) uncorrected astigmatism induce symptoms, especially @ 180°.  But it is not uncommon for small (<0,75 DC) uncorrected astigmatism, especially oblique or @ 90° to induce asthenopic symptoms since they tend to guide accommodation all the time towards the circle of least confusion.
  62. 62. When to prescribe LOGO PALs
  63. 63. When to prescribe LOGO Amblyopia risk  Astigmatism in children under the age of 3 years is liable.  Astigmatic refraction < 2,00 DC need not to be compensated. Premature prescribing may interfere with emmetropization.  Astigmatic refraction > 1,25 DC, especially in oblique axis, persisting after the age of 2 years, should be prescribed.  Astigmatic amounts that could reduce acuity, especially at near, or create symptoms need to be prescribed directly. Plasticity in young children is huge.
  64. 64. When not to prescribe or under-correct LOGO History of dizziness, disorientation, ear infections, etc. Small amounts, first time. Re-check, especially if habitual Rx had always been spherical. High cylindrical corrections. Check axis and amount at near. Consider under-correcting according to this findings.  When complaints are mainly at near and are unrelated to spherical equivalent, suspect cyclotorsion.
  65. 65. 3 strategies for better tolerance LOGO If changes in astigmatic refraction are >0.50 DC, consider decreasing cylinder by adjusting sphere.  Hab. Rx • -0.50 -1.25 X 180 O.U.  New Refraction • -0.50 -2.25 X 180 O.U.  New Rx (check) • -0,75 -1,75 X 180 O.U.
  66. 66. 3 strategies for better tolerance LOGO Approach equality in the cylindrical power, especially when axis are oblique.  Hab. Rx • O.D. -1.25 -0.50 X 145 / O.S. -1.25 -0.50 X 35  New Refraction • O.D. -0.75 -1.50 X 145 / O.S. -1.25 -0.75 X 35  New Rx (check) • O.D. -1,00 -1,00 X 145 / O.S. -1.25 -0.75 X 35
  67. 67. 3 strategies for better tolerance LOGO When patient reports failure of previous attempts with astigmatic correction or axis are very different from the habitual, consider prescribing spherical equivalent.  Hab. Rx • O.D. -5.00 -0.50 X 170 / O.S. -5.25 -0.50 X 180  New Refraction • O.D. -5.00 -0.50 X 115 / O.S. -5.25 -0.50 X 60  New Rx (check) • O.D. -5,25 / O.S. -5.50
  68. 68. Before you prescribe LOGO Keep axis as symmetrical as possible. Keep axis as close to main meridians as possible. Consult sensitive patients not to make significant changes in frame’s shape. Changes in base curve, pantoscopic angle and refractive index of material can alter magnification effects but usually patients adapt to in a few days.
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