1. Refractive Surgery Outcomes: Corneas Thinner than 500 microns Vs
Refractive Surgery Outcomes: Corneas Thinner than 500 microns Vs. Corneas Thicker than 500 microns
2LT Sarah Eccles Brown
New York Medical College
Charles D. Reilly, Lt Col USAF, MC, FS
Vasudha Panday, Maj, USAF, MC
Robert Lyons, Maj, USAF, MC, FS
Sanford Roberts, Lt Col, USAF, MC
Wilford Hall Medical Center, Lackland AFB TX
This research is government/military research and, therefore, the authors have no financial disclosures or conflicts of interest.

2. Purpose
To compare refractive surgery outcomes between patients with pre-operative central corneal thickness (CCT) <500 microns and those ≥500 microns.
To support the null hypothesis, stating there is no difference in refractive outcome between the two groups.

3. Methods
In this retrospective, non-randomized follow-up study, pre-operative pachymetry readings were obtained from 4,913 patient eyes through chart review and combined to existing patient databases.
Divided into preoperative CCT of < 500 microns (462 eyes) and ≥ 500 microns (4,451 eyes).
Patients receiving PRK and LASEK were included in the same category.

4. Methods
The pre-operative manifest spherical equivalent (MSE), uncorrected visual acuity (UCVA) at three and six months post-operatively, and the best corrected visual acuity (BCVA) at six months post-operatively were obtained for each group.
Linear regression analyses were plotted using the achieved versus attempted MRSE at 6 months post-operatively for both CCT groups.
Due to variability in patient follow-up and data documentation, the number of patient eyes varies for the three and six month follow-up results.

5. Research Results
N = 462, 457, N = 4451, 3796, 655

6. Research Results
N = 447, 442, N = 4325, 3292, 628

7. Research Results
N = 318, 316, N = 267, 267, N = 2846, 2486, N = 2524, 2186, 388

8. Research Results
N = 263, 263, N = 2478, 2147, 331

9. Linear Regression
Intercept
Slope
0.8964
N = 2135

10. Linear Regression
Intercept
Slope
0.8715
N = 228

11. Conclusions
Linear regression analyses showed similar slopes and y-intercepts between both CCT groups
No eyes in this data developed postrefractive corneal ectasia.
Refractive laser surgery with LASIK, PRK, or LASEK in patients with thinner corneas is as safe and predictable as the use of these techniques in patients with normal thickness corneas if patients are adequately screened pre-operatively.
Statistical analysis and additional longer term studies are needed to validate these early postoperative results.

12. Resource
Kymionis GD, Bouzoukis D, Diakonis V, et al. Long-term results of thin corneas after refractive laser surgery. Am J Ophthalmol Aug;144(2):