A recent study has measured the corneal topography of normal and keratoconic patients using the Topographic Modelling System (TMS). The study showed that keratoconus could be characterised using three indices:1. corneal dioptric power in the central ring; 2. the difference between the central power of each eye; and 3. the difference in dioptric power at locations 3 mm above and below the visual axis. We have derived confidence intervals from these data and illustrate their use in the diagnosis of keratoconus for an individual patient. Values outside the 95 per cent confidence interval for normal corneal topography are:1. central power ≤47.00 D; 2. right‐left eye asymmetry of ≤1.00 D; and 3. superior‐ inferior asymmetry of ≤1.50 D. These indices provided a quantitative basis for the diagnosis of keratoconus in this patient, and an equivocal diagnosis was thereby
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