Evaluation of myopic corneal diameter with the Orbscan II Topography System.

BACKGROUND

To assess the myopic corneal diameter with Orbscan II Topography System (Bausch & Lomb, Orbtek Inc., Salt Lake City, UT, USA).

METHODS

Four hundred sixty-two eyes of 231 myopic patients and 129 emmetropic eyes were measured with the Orbscan II system. Eyes were divided into four groups according to the spherical equivalent(SE) as follows: group 1 [emmetropic group, spherical equivalents between -0.50 D and +0.50 D (-0.50<SE ≤ +0.50)]; group 2 [low myopia group, spherical equivalent between -0.50 D and -3.00D (-3.00<SE ≤ -0.50)]; group 3 [median myopia group, spherical equivalent between -3.00 and -6.00D (-6.00<SE ≤ -3.00)]; and group 4 [high myopia group, spherical equivalents of -6.00D or less (≤-6.00)]. Manifest refraction results and the Orbscan II corneal topographic maps were reviewed retrospectively. Horizontal corneal diameters (white-to-white [WTW] distance) were measured with the Orbscan II system. Subjects in different groups were matched to be comparable in terms of spherical equivalents.

RESULTS

The corneal diameter in all myopic eyes was 11.49 ± 0.36 mm. There were no significant differences between right and left eyes in the t-test for paired samples (t = -0.119, P = 0.906). Differences among four groups proved to be significant in the ANOVA (F = 4.487, P = 0.004).

CONCLUSIONS

This article provides a detailed description and analysis of Orbscan II corneal diameter of a normal myopic population. High degree of mirror image symmetry existed in myopic corneal diameter. Spherical equivalents made a difference in corneal diameter.