The Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study
The Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study
To describe the clinical course of keratoconus and to describe the relationships among its
 visual and physiological manifestations, including high- and low-contrast visual acuity,
 corneal curvature, slit lamp biomicroscopic findings, corneal scarring, and quality of life.

 To identify risk factors and protective factors that influence the severity and progression
 of keratoconus.
Keratoconus is a bilateral, asymmetric, chronic, progressive ectasia of the cornea
 characterized by steepening and distortion of the cornea, thinning of the apical cornea,
 corneal scarring, and treatment-related sequelae, such as abrasions from contact lenses and
 surgical complications. Patients experience distorted vision that worsens with disease
 progression. Their vision is typically corrected with spectacles early in the disease and,
 later, with rigid contact lenses. Some patients eventually undergo corneal transplantation in
 one or both eyes. Keratoconus affects people in their prime earning years and profoundly
 affects their lives.

 Previous large-scale studies of keratoconus have focused on incidence and prevalence,
 etiologies, or the clinical management of keratoconus. Few have characterized the course of
 the disease and risk factors for its progression in large samples of keratoconus patients.
 The incidence of vision-threatening corneal scarring in keratoconus is unknown. Patient's
 most frequent questions--how rapidly their keratoconus will progress, how bad their vision
 will become, whether they will need corneal surgery, how successful their contact lenses will
 be--cannot be answered on the basis of the current body of knowledge.

 The need for a prospective, observational study of keratoconus patients is great. Results
 from this study will address keratoconus patient's unanswered questions and will enable eye
 care practitioners to manage this complex ocular disease better.

 The Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study is a multicenter,
 observational study of 1,209 keratoconus patients followed for 3 years.

 Patients are examined annually. Study measures include visual acuity, patient-reported
 quality of life, manifest refraction, keratometry, photodocumentation of the cornea to
 identify central corneal scarring, photodocumentation of the flattest contact lens that just
 clears the cornea, slit lamp biomicroscopy, and corneal topography. In rigid contact lens
 wearers, the fluorescein pattern of the patient's habitual contact lenses is photodocumented.

 Patients are examined at 15 clinical centers. The clinical centers enrolled 1,209 patients in
 12 months.
Patients with keratoconus were eligible if they were at least 12 years old; had an
 irregular cornea as determined by keratometry, retinoscopy, or direct ophthalmoscopy in at
 least one eye; had Vogt's striae, Fleischer's ring, or corneal scarring characteristic of
 keratoconus in at least one eye; and planned to stay in the area for at least 3 years. They
 were ineligible if they had bilateral corneal transplants or bilateral nonkeratoconic eye
 disease (cataract, intraocular lenses, macular disease, or optic nerve disease other than
 glaucoma).