Accuracy of Orbscan Pachymetry Measurements and Ultrasonic Pachymetry before and after LASIK with Orbscan II$^{\circledR}$ Topography

Purpose : To assess the the accuracy and variability in pachymetry measurements obtained by Orbscan and ultrasonic pachymeter in laser in situ keratomileusis (LASIK). Methods : Thirty two eyes of 16 patients before LASIK were measured by ultrasonic pachymeter and Orbscan. Thirty eyes of 16 patients that had LASIK were measured by ultrasonic pachymeter and Orbscan postoperatively. The theoretical residual corneal thickness was compared to measurements by both instruments in eyes that had LASIK procedures. Results: The ultrasound pachymeter measurements (543.824.2 ,urn) were thicker than the Orbscan pachymetry measurements, (541.224.9 ,urn) by mean of 2.77.4,urn (SD), preoperatively. But this is not statistically significant (p>O.05). Postoperatively, the ultrsound measurements were consistent with theoretical residual corneal thickness, 461.837.4,urn versus 467.930.71 ,urn (p=O.064), while Orbscan measurements were statistically less than the theoretical residual corneal thickness, 433.248.75 ,urn versus 464.3233.4,urn (p