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

Purpose

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).

Setting

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

Methods

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.

Results

The mean patient age was 32.4 ± 15.2 years. 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 μm at baseline to 343 ± 61 μm 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.

Conclusion

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