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Home » Resources » Clinical Studies » Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study, The

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Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study, The

Purpose | Background | Description | Patient Eligibility | Recruitment Status | Current Status | Results | Publications | Resource Centers | NEI Representative

Purpose

Background

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. Patients' 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 patients' unanswered questions and will enable eye care practitioners to manage this complex ocular disease better.

Description

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.

Patient Eligibility

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).

Patient Recruitment Status

Completed. As of June 15, 1996, 1,209 patients were enrolled. Enrollment began June 1, 1995. Patients will be examined annually thereafter.

Current Status of Study

Ongoing.

Results

None.

Publications

Fink BA, Barr JT, Edrington TB, Pierce GE, Schechtman KB, Rah MJ, Flom R, Zadnik K, the CLEK Study Group: A comparison of two methods of evaluating cornea-to-contact lens base curve fluorescein patterns in keratoconus. Optom Vis Sci 78: 589-598, 2001.

Szczotka LB, Barr JT, Zadnik K, the CLEK Study Group: A summary of the findings from the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study. Optometry 72: 574-587, 2001.

McMahon TT, Anderson RJ, Joslin CE, Rosas GA, the CLEK Topography Analysis Group: Precision of three topography instruments in keratoconus subjects. Optom Vis Sci 78: 599-604, 2001.

Raasch TW, Schechtman KB, Davis LJ, Zadnik K, the CLEK Study Group: Repeatability of subjective refraction in myopic and keratoconic subjects: results of vector analysis. Ophthalmic Physiol Opt 21: 376-383, 2001.

Zadnik K, Barr JT, Edrington TB, Nichols JJ, Wilson BS, Siegmund K, Gordon MO, the CLEK Study Group: Corneal scarring and vision in keratoconus: a baseline report from the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study. Cornea 19: 804-812, 2000.

Barr JT, Zadnik K, Wilson BS, Edrington TB, Everett DF, Fink BA, Shovlin JP, Weissman BA, Siegmund K, Gordon MO, the CLEK Study Group: Factors associated with corneal scarring in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study. Cornea 19: 501-507, 2000.

Barr JT, Schechtman KB, Fink BA, Pierce GE, Pensyl CD, Zadnik K, Gordon MO, the CLEK Study Group: Corneal scarring in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study: baseline prevalence and repeatability of detection. Cornea 18: 34-46, 1999.

Edrington TB, Szczotka LB, Barr JT, Achtenberg JF, Burger DS, Janoff AM, Olafsson HE, Chun MW, Boyle JW, Gordon MO, Zadnik K, CLEK Study Group: Rigid contact lens fitting relationships in keratoconus. Optom Vis Sci 76: 692-699, 1999.

Zadnik K, Barr JT, Edrington TB, Everett DF, Jameson M, McMahon TT, Sterling JL, Wagner H, Gordon MO, the CLEK Study Group: Baseline findings in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study. Invest Ophthalmol Vis Sci 39: 2537-2546, 1998.

Edrington TB, Szczotka LB, Begley CG, Burger DS, Wilson BS, Barr JT, Zadnik K, Gordon MO, CLEK Study Group: Repeatability an dagreement of two corneal curvature assessments in keratoconus: keratometry and the first definite apical clearance lens (FDACL). Cornea 17: 267-277, 1998.

Davis LJ, Schechtman KB, Begley CG, Shin JA, Zadnik K, the CLEK Study Group: Repeatability of refraction and corrected visual acuity in keratoconus. Optom Vis Sci 75: 887-896, 1998.

Gordon MO, Schechtman KB, Davis LJ, McMahon TT, Schornack J, Zadnik K, the CLEK Study Group: Visual acuity repeatability in keratoconus: impact on sample size. Optom Vis Sci 75: 249-257, 1998.

Barr J, Gordon MO, Pellican K, Zadnik K, Edrington TB, Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study Group: A corneal scarring photodocumentation and reading method. J Refract Surg 12: 492-500, 1996.

Edrington TB, Barr JT, Zadnik K, Davis LJ, Gundel RE, Libassi DP, McMahon TT, Gordon MO: A standardized rigid contact lens fitting protocol for keratoconus. Optom Vis Sci 73: 369-375, 1996.

Gundel RE, Libassi D, Davis LJ, McMahon TT, Edrington TB, Zadnik K, Barr JT, Gordon MO: Feasibility of fitting contact lenses with apical clearance in keratoconus. Optom Vis Sci 73: 729-732, 1996.

Zadnik K, Gordon MO, Barr JT, Edrington TB, Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study Group: Biomicroscopic signs and disease severity in keratoconus. Cornea 15: 139-146, 1996.

Resource Centers

Chairman's Office
Karla Zadnik, OD PhD
The Ohio State University
College of Optometry
338 West Tenth Avenue
Columbus, OH 43210-1240
Telephone: (614) 292-6603
Fax: (614) 292-4705
E-mail: zadnik.4@osu.edu
http://www.optometry.ohio-state.edu/CLEK/

Coordinating Center
Mae O. Gordon, PhD
Washington University Medical School
Department of Ophthalmology and Visual Sciences
Division of Biostatistics
Campus Box 8203
660 South Euclid Avenue
St. Louis, MO 63110-1093
Telephone: (314) 362-3716
Fax: (314) 747-1325
E-mail: mae@wubios.wustl.edu

CLEK Photography Reading Center
Joseph T. Barr, OD MS
The Ohio State University
College of Optometry
338 West Tenth Avenue
Columbus, OH 43210-1240
Telephone: (614) 292-9511

NEI Representative

Donald F. Everett, MA
National Eye Institute
National Institutes of Health
Executive Plaza South, Suite 350
6120 Executive Boulevard
Rockville, MD 20892
Telephone: (301) 496-5983
Fax: (301) 402-0528

Last Updated: 11/2/01



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