The document provides guidelines for determining the best glasses prescription for patients with keratoconus based on their topography patterns, including starting with the least minus sphere and small cylinder to maximize vision while minimizing distortion, using binocular trials to account for changes from torsion and accommodation, and considering anisometropia and ways to improve binocularity. It discusses different approaches for central cone, oval cone, snowman, and peripheral cone patterns identified on topography.

1. Glasses Prescription
for Keratoconus
· Mohamed Zaky Elkadim MD
· Cornea Unit-Tanta University
· 5/8/2021

2. ‫الرحيم‬ ‫الرحمن‬ ‫هللا‬ ‫بسم‬

3. Importance
· Most patients could have satisfactory
vision with glasses
· Spare for RGP

4. Patient own glasses -1/-1 x 30
Auto ref -5 / -3.5 x 34
1st trial - 1.5 / - 1.5 x 35 ===== 0.5
2nd trial + 1.00 / -2.5 x 70 ===== 0.7

5. No Autoref

6. Subjective Refraction
Guided by Pentacam

7. Pentacam
· Provide starting point for trial.
· Decrease dependence on the patient
· (important in children)

8. Pentacam Classification of
keratoconus
1) Central cone
2) Oval cone (paracentral)
3) Snowman (paracentral)
4) Peripheral cone

9. Central cone
Central island ,, high central K
,, low astigmatism

11. Central cone
· Find the Sphere.
(least minus / no autoref)
· Most of this patients will have
only myopia
· Try small cylinder keeping the
SE.

12. Oval cone
Protruded tongue ,
low K , high astigmat

14. To find axis draw a line bisecting the flattest
color (green)

18. Especially in the case of irregular
astigmatism, patients accept only a smaller
subjective cylinder than the objective
cylinder measured by keratometry or
topography analysis
· Seitz B, Langenbucher A, Küchle M, Naumann GOH. Impact of
graft diameter on corneal power and the regularity of post
keratoplasty astigmatism before and after suture removal.
Ophthalmology. 2003;110:2162–7.

19. In astigmatism, correction with
spectacles produces different
magnifications in the two principal
meridians. This can give rise to
perceived distortion of space

20. · Give the patient the least
cylinder that give the BCVA
90
-3.5
-5
90
-3
-5.25
90
-2.5
-5.5

22. Topographic axis may be wrong

24. Autorefractor is also wrong

25. Other case

28. Snowman

30. Bisect the blue to find the axis

31. Autoref always wrong

32. Peripheral cone
· Most Benign
· Can use Autoref or Topographic
astigmatism

34. Binocular Trial

35. In binocular condition
· Torsion of eyes can change (Axis)
· Accommodation can change (sphere)

36. +2
+0.25
+0.5
Relax the accommodation with +2 infront
of one eye and gradually add + infront of
the other to find the least minus sphere

37. +2 +0.25

38. Compare with Pin hole acuity

39. Anisometropia

40. What could be done to
improve binocularity ?
-2 D
- 7 D
-2
-6.25
Power
↓
BVD
1.47
White plastic
1.7 – 1.8
Glass
RI

41. Phoroptor or Frame ?

42. Problem of phoroptor
Can be misleading in sphere

43. Problem of Frame

44. Problem of Frame