Keratoconus evaluation using the Orbscan Topography System

Purpose: To evaluate corneal topography in a series of keratoconus patients using the Orbscan Topography System. Setting: Department of Ophthalmology, Ruprecht-Karls-University of Heidelbe rg, Heidelberg, Germany. Methods: Seventy-one eyes of 38 patients with keratoconus were evaluated. Q uantitative topographic parameters were analyzed with special reference to the central point of the cornea, the apex (the point with maximum reading o n the anterior elevation best-lit sphere map), and the thinnest point. Eval uation included location, elevation (compared to a best-fit sphere), pachym etry, tangential curvature, and composite curvature. The mirror-image symme try between the right and left eyes of a patient was also investigated. Results: Mean patient age was 31.2 years +/- 12.2 (SD). Thirty-three patien ts (86.8%) had bilateral keratoconus and 5 (13.2%), unilateral keratoconus. Most cones (68/71) were located in the inferior temporal quadrant; 3 were above the horizontal meridian. Mean distance between the apex and the thinn est point was 0.917 +/- 0.729 mm (P < .001). The correlations between apex elevation and apex composite curvature and apex tangential curvature were h igh (r = 0.94 and r = 0.91, respectively; P < .001), In right and left eyes , there was a correlation between the apex and the thinnest point semi-meri dians (r = 0.47 and r = 0.65, respectively; P < .05) but not between the ra dii of the apex and the thinnest point (r = 0.21 and r = 0.24, respectively ). Conclusions: The Orbscan system can provide useful and accurate information in defining the morphology of keratoconus and detecting subtle topographic changes present in early keratoconus. it may also improve the results of c ontact lens fitting and surgical management. (C) 2000 ASCRS and ESCRS.