Computerized corneal tomography and associated features in a large New Zealand keratoconic population

PURPOSE: To evaluate corneal tomographic features of keratoconus and associations between risk factors and disease phenotype in New Zealand. SETTING: Departments of Ophthalmology, University of Auckland and Auckland District Health Board, Auckland, New Zealand. DESIGN: Clinic-based, cross-sectional study. METHODS: The medical records and corneal tomography of patients attending a subspecialty service were reviewed. Data included age, sex, ethnicity, ocular history, family history, atopy, and eye rubbing. Orbscan II parameters included simulated keratometry, mean power, pachymetry, location of maximum power, anterior best-fit sphere (BFS) and posterior BFS. Morphology was categorized by the Rabinowitz topography classification. RESULTS: Final analyses included 532 eyes (266 patients; 144 men) with a mean age of 29.3 years +/- 11.56 (SD). Maori and Pacific patients were overrepresented (P=.0001). Family history of keratoconus was associated with a lower mean corneal power (P=.01) and greater pachymetry (P=.03). Comparing patients with family history and patients with atopy, showed differences in thinnest-point pachymetry (mean: family history, 340 +/- 15 mu m; atopy 381 +/- 8 mu m) (P=.0218). Keratoconus was classified as severe (58.3%) or moderate (33.8%) on mean keratometry. Axial keratometric maps were predominantly asymmetric bow-tie (29%), round (18%), or inferior steepening (17%). Anterior elevation maps were classified as spur (49.3%), island (24%), irregular ridge (15%), or other (11.3%). Eighteen patients (12.5%) had complete enantiomorphism. CONCLUSIONS: Advanced keratoconus was largely asymmetric and differences in tomographic phenotype were associated with differing etiologic risk factors. Maori and Pacific ethnicities were overrepresented in this population.