Evaluation of keratoconus in Asians: Role of Orbscan II and Tomey TMS-2 corneal topography

PURPOSE: To evaluate the corneal topographic patterns of Asian patients with keratoconus (KC). DESIGN: Prospective observational case-control study. METHODS: SETTING: Institutional. STUDY POPULATION: A total of 116 patients (both eyes included) with KC were recruited. The control group consisted of 70 laser in,situ keratomileusis (LASIK) candidates with myopia. Patients with previous ocular surgery and trauma were excluded. OBSERVATION PROCEDURE: Corneal topography was performed using the Tomey KC screening system (Topographic Modeling System, software version 2.4.2J, Tomey Corp, Nagoya, Japan) and Orbscan 11 corneal topography system (Bausch & Lomb Surgical, Orbtek Inc, Salt Lake City, Utah, USA). MAIN OUTCOME MEASURES: Videokeratographic variables were analyzed and the eyes were grouped into KC, KC suspect, and control groups. RESULTS: The corneal topographic patterns of 196 eyes were analyzed. The topographic patterns displayed by Tomey (TMS-2N) and Orbscan 11 were similar. The majority of eyes with KC (71.2%) and KC suspect (70%) had asymmetric bowtie patterns. Thirteen indices of TMS-2N were analyzed and the means of the indices were found to be significantly higher in eyes in the KC group than the KC suspect group (P <.001). Fourteen indices of Orbscan 11 were analyzed. Eyes in the KC suspect group had higher mean posterior elevation (46 +/- 17 mu m), 3 mm irregularity (2.44 +/- 1.36 diopters [D]), 5 mm irregularity (2.61 +/- 1.19 D) and had thinner corneas (mean 504.4 +/- 40.4 mu m) than normal eyes (26 8 mu m, 1.05 +/- 0.37 mu m, 1.38 +/- 0.39 mu m, and 554.0 +/- 25.0 mu m, respectively). CONCLUSION: Corneal topography pattern recognition combined with quantitative diagnostic indices is useful for the screening and classification of KC with the Orbscan 11 being more sensitive in screening for KC than TMS-2N.