Evaluation of normal corneas using the scanning-slit topography/pachymetry system

To obtain anterior and posterior corneal shape, curvature, and thickness of normal human corneas. To provide a semiquantitative analysis of normal topography patterns of the anterior and posterior corneal surfaces.

Eighty-eight healthy corneas of 44 normal subjects were analyzed using the scanning-slit topography/pachymetry system. Anterior and posterior elevation and mean power (central and steepest spherical and cylindrical) values and pachymetry data were determined. Right eye values were submitted for primary analysis; however, a comparison between right and left eyes was made in addition to test the possible reliability of the system.

There was no significant difference between right and left corneas in 28 evaluated parameters, except for anterior central cylindrical (P = 0.005) and steepest cylindrical (P = 0.017) mean power. The anterior central spherical mean power correlated inversely with the posterior central spherical mean power (r = -0.27, P = 0.04), and the anterior steepest spherical mean power value showed inverse correlation with the mean posterior steepest spherical value (r = -0.44, P = 0.001). The mean central thickness of the cornea was 593.7 +/- 54.19 microm at the center and was 578 +/- 50.53 microm at the thinnest point, which was localized in 41% (n = 18) of the cases in the inferotemporal quadrant. An oval-shaped pattern was the most characteristic feature of the anterior and posterior elevation, mean power, and pachymetry maps.

Orbscan scanning-slit topography seems to be a reliable technique for the evaluation of normal corneas not only for anterior shape and curvature but also for a real pachymetry gradient recording.