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 (r² = 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.