Evaluation of Orbscan II corneal topography in individuals with myopia

Abstract

Purpose: To evaluate Orbscan II (Bausch & Lomb, Orbtek Inc., Salt Lake City, UT) corneal topography in individuals with myopia.

Design: Retrospective, observational, consecutive, clinical case series.

Participants: One hundred forty eyes of 70 persons with myopia.

Methods: Manifest refraction results and the Orbscan II corneal topographic maps were reviewed retrospectively.

Main outcome measures: Refractive powers and the following test indices produced by Orbscan II were analyzed: anterior elevation best-fit sphere (BFS), posterior elevation BFS, maximum posterior elevation (Max PE), radius of Max PE, maximum keratometry, minimum keratometry, astigmatism, 3-mm irregularity, 3-mm mean power, 3-mm astigmatism, 5-mm irregularity, 5-mm mean power, 5-mm astigmatism, corneal diameter, pupil diameter, thinnest pachymetry, and anterior chamber depth. The correlations between right eyes and left eyes and between indices were explored.

Results: Of the 140 eyes, the mean manifest refraction was -5.27+/-2.19 diopters (D; range, -10.50 to 0.00 D), the mean Max PE was 28+/-7 mum, and the mean maximum keratometry was 44.5+/-1.5 D. Correlation coefficient analyses of Orbscan II quantitative indices combined with pattern recognition showed that there were high degrees of correlations between the right and left eyes of each individual patient. Maximum posterior elevation, corneal irregularity, and thinnest pachymetry did not vary with the degree of maximum keratometry.

Conclusions: This article provides a detailed description and analysis of Orbscan II corneal topography of a normal population with myopia. This helps in establishing normal standards in Orbscan II corneal topography that will aid in preoperative assessment in refractive surgery.