Reliability of pachymetric measurements using orbscan after excimer refractive surgery.

Purpose: To assess the accuracy of pachymetric measurements using Orbscan (Bausch & Lomb, Rochester, NY) after laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK).

Design: Prospective instrument validation study.

Participants: Seventy-nine nonoperated normal eyes, 84 eyes after LASIK, and 50 eyes after PRK.

Intervention: Laser in situ keratomileusis or PRK.

Methods: Central corneal thickness was measured using ultrasound and Orbscan II. The acoustic factor (AF) was adjusted, based on the results obtained in the normal eye group, to minimize the difference between ultrasound and Orbscan pachymetric values.

Main Outcome Measures: Central corneal thickness as measured by Orbscan and ultrasound pachymeter.

Results: Using the adjusted AF, which was 0.946, the mean difference between Orbscan and ultrasonic pachymetric measurements was 0 +/- 17, 16 +/- 28, and 68 +/- 39 microm in the normal, LASIK, and PRK groups, respectively. The difference between all groups was statistically significant (P < 0.0001).

Conclusions: Orbscan pachymetric values may be underestimated and less accurate after LASIK and PRK.