This presentation describes how to deal with prelasik case and what are the tips you should not miss in prelasik evaluation.

1. PRELASIK EVALUATION
BY
Dr. Amr Mounir
Lecturer of ophthalmology
Sohag university

2. Includes
1. Accurate refraction
evaluation.

3. 2- Corneal topography
2- Corneal topography
Aim : to avoid ectasia

4. Aim of corneal topography
To avoid post lasik
ectasia by
exclusion of
suspicious cornea

5. Refraction:
Like glasses with following tips:
In Myopia :
Correct the full correction especially in young
candidates
In Hypermetropia:
Over correct due to high liability of regression
in HMT

6. Importance of cycloplegic refraction
In Myopia :
-Cycloplegic < manifest
-Avoid difference > 1Ds
In Hypermetropia :
- Cycloplegic > manifest
- May be marked
difference
- Be near cycloplegic in
tttt

7. What Pentacam says to us???
Pachymetry map
Keratometry map ( K1,K2,Kmax)
Elevation map
Provisional diagnosis: Keratoconus Summary (Sirus
device)
Aberration map
Scheimpflug imaging

8. Examples

9. 4 Maps

10. Aspherotoric map

11. Keratoconus summary map

12. 4 Maps: Inferior steepening

13. Aspherotoric map: High back elevation

14. Keratoconus summary map

15. 4 Map : Horizontal bow tie

16. Summary map

17. Pellucid Marginal Degeneration (PMD) and Pellucid-like
Keratoconus
- PMD is a bilateral, non-inflammatory, peripheral corneal
thinning disorder characterized by a peripheral band of
thinning of the inferior cornea. The cornea in and adjacent
to the thinned area is ectatic.
- Patients usually are aged 20–40 years at the time of
clinical presentation.

19. Options For Treatment

20. LASIK OR PRK ????

21. LASIK OR PRK ????
LASIK
- Normal Pentacam
- Sufficient thickness
- Normal retina
- Clear cornea
- More dry eye
- Rapid rehabilitation
PRK
- Suspicious Pentacam
-Thin cornea
- Peripheral retinal
degenerations
- - Faint superficial
opacities
- Less dry eye
- Slow rehabilitation

22. Corneal thickness and correction

23. Corneal thickness and correction
- Every 1Ds correction will remove about of 10 um of the
corneal stroma
- The residual bed shouldn't be less than 300 um to avoid
post Lasik ectasia.
- The residual bed = Thinnest location - [ablation depth ( ttt)
+ flap thickness]

24. Keratometry and correction

25. Keratometry and correction
For Myopic Correction :
- Every 1 Ds correction will decrease
Keratometry by 0.8 Ds.
- Avoid to decrease the flattest K below 34
Ds to avoid aberrations

26. Keratometry and correction
For Hypermetropic Correction :
- Every 1 Ds correction will increase
Keratometry by 1.00 Ds.
- Avoid to increase the steepest K above 50
Ds to avoid aberrations

27. Age as a guideline for decision

28. Age as a guideline for decision
In Young age < 30 ys
Full or over correction is recommended to
compensate for future regression
In old age > 30 ys
Full correction is recommended or even slight under
correction is needed especially in presbyopic
patients.

29. Thank you