Purpose-To describe baseline and longitudinal findings of the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study.Methods-The CLEK Study is an eight-year, multi-center, natural history study of 1,209 patients with keratoconus who were examined annually for eight years. Its goals are to prospectively characterize changes in vision, corneal curvature, corneal status, and vision-specific quality of life.Results-CLEK Study subjects had a mean age at baseline of 39.3 +/− 10.9 years. At study entry, 65% of the patients wore rigid contact lenses, and 14% reported a family history of the disease. Subjects exhibited a seven-year decrease in high-(2.03 letters) and low-(4.06 letters) contrast, best-corrected visual acuity, with 19% demonstrating decreases of 10 or more letters in high-contrast, best-corrected acuity and 31% of subjects demonstrating decreases of 10 or more letters in low-contrast, best-corrected acuity in at least one eye. Subjects exhibited an average eight-year increase in corneal curvature of 1.60 D in the flat corneal meridian, with 24% demonstrating increases of 3.00 D or more. The eight-year incidence of corneal scarring was 20%, with younger age, corneal staining, steeper baseline corneal curvature, contact lens wear, and poorer low-contrast visual acuity predictive of corneal scarring. Data from the National Eye Institute Visual Function Questionnaire suggest that the effect of keratoconus on vision-specific quality of life is disproportionate to its low prevalence and clinical severity.Conclusion-Although we report measures of disease severity and visual function across the CLEK sample, clinicians can begin to envisage the course of keratoconus in individual patients by determining whether factors predictive of disease progression are present in those patients.

Overnight orthokeratology is an effective means of temporarily reducing myopia. The possible mechanism of corneal remodeling through central corneal thinning is discussed.

A simple and reliable grading system for keratoconus was developed that can be largely automated. Such a grading scheme could be useful in genetic studies for a complex trait such as keratoconus requiring a quantitative measure of disease presence and severity.