Comparison between Posterior Corneal Surface Changes after LASIK Measured by Sirius Pentacam and Orbscan IIz

Abstract
Purpose: To investigate the reliability of Sirius Pentacam and OrbscanIIz in evaluating posterior corneal surface changes after LASIK.
Methods: This prospective observational case series study was conducted on thirty eyes of 15 patients underwent LASIK for myopia with or without myopic astigmatism at both the Ophthalmology Department of Tanta Universal Teaching Hospital and Nour El-Ein Hospital. OrbscanIIz and Sirius Pentacam examination (CSO, Firenze, Italy) were performed after LASIK to study their reliability in evaluating posterior corneal surface changes after LASIK.
Results: The mean elevation of the highest points on posterior corneal elevation maps after LASIK by Orbscan and Sirius was 35.47±11.6mm (range from 14mm to 49mm) and 9±2.9mm (range from 5mm to 16mm) respectively with no statistically significant difference between the values measured by the two methods (p-value 0.06). Regarding the maximal highest point on posterior corneal elevation maps by Orbscan and Sirius was 50mm and 17mm respectively, the difference of means by Orbscan and Sirius was 14.53 and 8 respectively, the limits of agreement from –8.2 to 37.3 by Orbscan and 2.4 to 13.6 by Sirius respectively. The coefficient of repeatability was 36.20% by Orbscan and 16.60% Sirius, hence Orbscan is better than Sirius.
Conclusions: There was no statistically significant differ-ence between the values measured by Orbscan IIz and Sirius (p-value 0.06). The coefficient of repeatability was 36.20% by Orbscan and 16.60% Sirius, hence Orbscan is better than Sirius. Surface irregularity has benefit to detect abnormal corneal topography with normal value about ±2 within 3mm zone or ±2.5 within 5mm zone. It is not present in Sirius but only Orbscan and this is one of advantages of Orbscan.