Relationship between the corneal surface and the anterior segment of the cornea: An Asian perspective

PURPOSE: To determine the values for the anterior best-fit sphere (BFS) and posterior BFS in an Asian population using the Orbscan II (Bausch & Lomb) slit-scanning Placido disk corneal topographer. SETTING: Hospital-based refractive surgery center. METHODS: This prospective nonrandomized study comprised of 1 eye of 724 subjects. The eyes were measured with the Orbscan II. Default settings were used to generate relative elevation maps. Anterior BFS, posterior BFS, mean keratometry (K-mean), spherical equivalent (SE), horizontal white-to-white size (WTW), and anterior chamber depth (ACD) were analyzed. RESULTS: The mean spherical equivalent (SE) in the 724 eyes was -5.32 diopters (D) +/- 2.88 (SD). The anterior BFS and posterior BFS were normally distributed, with a mean of 43.05 +/- 1.37 D and 52.43 +/- 2.03 D, respectively. The regression equation of anterior BFS and posterior BFS was posterior BFS = 0.443 + 1.208 anterior BFS (r(2) = 0.667, P<.01). The ratio of posterior BFS to anterior BFS was 1.22 +/- 0.03. The anterior BFS was significantly correlated to posterior BFS (P<.01), K-mean (P<.01), and horizontal WTW (P<.01) but not to SE (P =.28). The posterior BFS was significantly correlated to K-mean (P<.01) and the horizontal WTW (P<.01) but not to SE (P =.70). CONCLUSION: There was a close relationship between the various corneal parameters, which is significant in refractive surgery and intraocular lens calculation and design.