Role of Orbscan II in screening keratoconus suspects before refractive corneal surgery

Objective: To evaluate the relationship between videokeratographic keratoconus screening programs and Orbscan II topography. Design: Prospective, observational case series and instrument validation study. Participants: Sixty consecutive eyes with suspicious videokeratography (TMS-1, Tomey Technology, Waltham, MA) were evaluated before undergoing laser in situ keratomileusis (LASIK) surgery. A control group of 50 consecutive eyes without suspicious features by videokeratography was also evaluated. Methods: Keratoconus screening programs, using the Rabinowitz and Klyce/Maeda methods and Orbscan II (Bausch & Lomb, Claremont, CA) topographies were performed on these patients. Main Outcome Measures: Specific parameters evaluated on the Orbscan II topographies were anterior elevation, posterior elevation, and thinnest pachymetry. Results: Compared with a control group of patients without suspicious videokeratography, there was a statistically significant difference in the mean posterior elevation and mean anterior elevation in the groups with positive keratoconus testing with the Rabinowitz or Klyce/Maeda methods. For patients who met both the Rabinowitz and Klyce/Maeda criteria for keratoconus, the mean posterior elevation was 44 +/- 2.5 mum compared with a posterior elevation of 21 +/- 0.6 mum for the control group. There was no statistically significant difference in the mean thinnest pachymetry between the control group and all keratoconus suspect groups. Conclusions: Patients with positive keratoconus screening tests have higher anterior and posterior elevation on Orbscan II topography. When used in combination with videokeratography, the Orbscan II topography system may be helpful in identifying patients who are potentially at high risk for developing ectasia after LASIK.