Purpose. The multicenter Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study is a prospective, observational study of 1,209 keratoconus patients. We report on the correlation of corneal scarring with clinical and patient-reported variables at the baseline visit. Methods. Patients completed a questionnaire on their vision, effect of glare, contact lens wear, and work-related issues. Clinical examination included high- and low-contrast visual acuity, refraction, assessment of corneal scarring by the clinician and by photography, and measurement of corneal curvature. The correlation of central corneal scarring with visual acuity and patient-reported variables was analyzed using multiple regression analysis and generalized estimating equations. Results. High- and low-contrast visual acuity with habitual and optimal correction is reduced in scarred eyes. Multiple regression analyses controlling for age, contact lens wear, and disease severity show that central scarring is associated with poorer visual acuity and increased patient-reported symptoms of glare. Restrictions on day-to-day activities do not appear to be associated with corneal scarring above and beyond the effects of keratoconus alone. Conclusions. Corneal scarring in keratoconus is significantly associated with decreased high- and low-contrast visual acuity.