Between-eye asymmetry in keratoconus.

PURPOSE: To report baseline differences between eyes on key variables in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study cohort compared with a retrospectively assembled group of myopic contact lens wearers without ocular disease. METHODS: A total of 1,079 keratoconus patients who had not undergone a penetrating keratoplasty in either eye before their baseline visit were enrolled and examined at baseline. Records from 330 contact lens-wearing myopes were reviewed. Corneal curvature (keratometry), visual acuity, refractive error (manifest refraction), and corneal scarring were measured. RESULTS: The mean differences between keratoconic eyes are as follows (better eye-worse eye for each variable, separately). Flat keratometry: -3.59 +/-4.46 D and steep keratometry: -4.35 +/-4.41 D; high-contrast best-corrected visual acuity: 7.30 +/-6.83 letters; low-contrast best-corrected visual acuity: 8.53 +/-7.51 letters; high-contrast entrance visual acuity: 9.03 +/-8.40 letters; low-contrast entrance visual acuity: 9.43 +/-7.88 letters; spherical equivalent refractive error: 3.15 +/-3.84 D; and refractive cylinder power 1.55 +/-1.42 D. Twenty-one percent of the keratoconus patients had corneal scarring in only one eye. There is an association between patient-reported unilateral eye rubbing and greater asymmetry in corneal curvature, and between a history of unilateral eye trauma and greater asymmetry in corneal curvature and refractive error, with the rubbed/traumatized eye being the steeper eye most of the time. CONCLUSIONS: Keratoconus is asymmetric in the CLEK Study sample.