Purpose: To identify a population of keratoconus patients with unilateral disease based on clinical findings and slit-lamp biomicroscopy and examination with a nine-ring photokeratoscope (Corneascope) and to study the topography of the clinically normal fellow eye with videokeratography. Methods: Clinical charts and Polaroid Corneascope photographs of both eyes of 200 patients with a diagnosis of keratoconus from three large cornea referral practices in the Los Angeles area were retrospectively reviewed. Patients whose clinical findings were within normal limits and whose Corneascope Polaroid photographs had concentric rings with no detectable abnormalities, consistent with a diagnosis of keratoconus in one eye, were considered unilateral: These patients were recalled to our clinic, and the topography of the apparently normal eye was studied using a Corneascope and a computer-assisted videokeratoscope, the Topographic Modeling System, on the same day. Results: Based on examination with a slit-lamp biomicroscope and the Corneascope, eight patients had unilateral disease. Videokeratography in seven of the eight fellow eyes displayed a pattern of inferior steepening suggesting "early keratoconus." All seven eyes had a positive “I — S value,” a quantitative measure, indicating increased dioptric power below the corneal apex. Conclusion: Our findings suggest that keratoconus is almost always bilateral. These data support genetic influences in the pathogenesis of this disorder. Additionally, videokeratography data presented might prove useful in the detection of early keratoconus and refining patient selection for myopic keratorefractive procedures.
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