Two-year interval changes in Orbscan II topography in eyes with keratoconus

To define topographic characteristics and quantitatively document changes in corneal topography parameters in relation to the progression of keratoconus over time using the Orbscan II topography system (Bausch & Lomb).

Eskisehir Osmangazi University Medical School, Department of Ophthalmology, Meselik, Eskisehir, Turkey.

This study comprised 79 eyes (79 patients) with keratoconus who had Orbscan II topography examinations at least twice with a mean interval of 24 months +/- 3.2 (SD). Topographic parameters including location radius, elevation compared to a best-fit sphere, pachymetry, mean tangential curvature, and mean spheric curvature were evaluated with special reference to the central point of the cornea, the apex, and the thinnest point. The change in each parameter was calculated using the paired t test.

The mean patient age was 31.6 +/- 14.9 (SD) [corrected] The increase in apex elevation (mean: 0.056 +/- 0.033 mm baseline versus 0.069 +/- 0.037 follow-up) (P<.02) and displacement of the location of the apex were statistically significant. The mean thinnest-point pachymetry decreased from 369 +/- 53 mum at baseline to 343 +/- 61 mum at follow-up (P = .03). The mean simulated keratometry minimum value was 48.21 +/- 5.5 diopters (D) and 54.09 +/- 6.2 D, respectively, a statistically significant increase (P = .02). The mean radius, mean elevation, mean tangential, and mean spheric curvatures of the apex did not change significantly.

The Orbscan II topography system provided useful and detailed numerical information on keratoconic corneas and documented their progression quantitatively by serial topographic analysis.