Evaluation of myopic corneal diameter with the Orbscan II Topography System

To assess the myopic corneal diameter with Orbscan II Topography System (Bausch & Lomb, Orbtek Inc., Salt Lake City, UT, USA). 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 a parts per thousand currency signaEuro parts per thousand+0.50)]; group 2 [low myopia group, spherical equivalent between -0.50 D and -3.00D (-3.00 < SE a parts per thousand currency signaEuro parts per thousand a'0.50)]; group 3 [median myopia group, spherical equivalent between -3.00 and -6.00D (-6.00 < SE a parts per thousand currency signaEuro parts per thousand a'3.00)]; and group 4 [high myopia group, spherical equivalents of -6.00D or less (a parts per thousand currency signa'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. 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). 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.