Background
Keratoconus is a thinning disorder of the central cornea resulting in visual distortion. It is usually treated with rigid contact lenses when spectacles no longer provide adequate vision.
The CLEK Study
The Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study was a multi-center, observational study. The CLEK Study’s purpose was to prospectively characterize vision, corneal changes, and patient quality of life findings in keratoconus and to determine the progression of changes occurring with keratoconus over time.
The CLEK Study was an eight-year study. Over 1,200 keratoconus patients were enrolled at 15 participating clinics across the United States. These patients were examined at the enrollment (between May 1995 and June 1996) and annually through 8 years of followup (the last 8-year followup was completed in August 2004).
The CLEK Study evaluated keratoconus patients’ quality of life, case history findings, contact lens wearing time, visual acuity, corneal findings, corneal scarring, corneal topography, mode of treatment, contact lens fit, rigid contact lens base curve radius just clearing the corneal apex, corneal photography, and fluorescein pattern photography.
Specific Aims
The CLEK Study had four Specific Aims, as outlined in its funding grant and the Manual of Procedures:
- Specific Aim A: General Description of the Course of Keratoconus. To describe the distribution and rate of change in best corrected high and low contrast visual acuity, corneal curvature, the proportion of patients developing incident corneal scarring, and the proportion of patients progressing to surgical intervention.
- Specific Aim B: Factors Related to Vision in Keratoconus. To characterize the association between best corrected visual acuity and visual quality of life and each of several pre-defined covariates. Acuities were measured using high and low contrast Bailey-Lovie charts. Visual quality of life was measured using the SF-36 and NEI-VFQ. The covariates of interest were corneal curvature, corneal irregularity, corneal scarring, the patient’s age, whether the patient wears spectacles or contact lenses, the type of contact lens worn, and the first definite apical clearance contact lens base curve.
- Specific Aim C: Factors Related to Disease Progression (Corneal Curvature) in Keratoconus. To characterize the relationship between corneal curvature, as measured by keratometry, and each of several pre-defined covariates. The covariates of interest were corneal irregularity, corneal scarring, the patient’s age, whether the patient wears spectacles or contact lenses, and the type of contact lens worn.”
- Specific Aim D: Factors Related to Corneal Scarring. To determine the relationship between corneal scarring, measured by a standardized photography and reading method, and each of several pre-defined covariates. The covariates of interest were corneal curvature, the patient’s age, high and low contrast best corrected an habitual visual acuity, whether the patient wears spectacles or contact lenses, the type of contact lens worn, and the first definite apical clearance contact lens base curve.
Data Monitoring and Oversight Committee
Responsibility for monitoring the conduct of the Study and for monitoring the accumulating data is assigned to the Data Monitoring and Oversight Committee. This committee provides recommendations to the Director of the National Eye Institute and to the CLEK Executive Committee regarding when findings from the CLEK Study may be released to the Study investigators, to Study patients, and to the vision community. This committee also oversees the informed consent process, major changes to the protocol, and Participating Clinic performance.
Status (August, 2005)
The last CLEK patient followup visit was completed in August, 2004, and no additional data collection is planned. Data analysis and interpretation continue, however, and a number of manuscripts are in preparation or planned.
Acknowledgements
The CLEK Study was funded by the National Eye Institute, a division of the National Institutes of Health, grants U10 EY10419, EY10069, and EY10077.