OM t of c.iii - Vision Research Coordinating Center - Washington ...

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2/1/99 Chapter 2 Study Design page 2-3 acuity and visual quality of life and each of several pre-defined covariates. Best corrected and habitual visual acuity will be measured using high and low contrast Bailey-Lovie charts. Visual quality of life will be measured using the SF-36 and Javitt Visual Function Questionnaire. The covariates of interest are 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. We will seek to determine what measure of visual acuity—high or low contrast with best correction, habitual correction, or manifest refraction and with either eye, the better eye, or both eyes—best predicts visual quality of life. 2.2.3 Specific Aim C. Factors Related to Disease Progression (Corneal Curvature) in Keratoconus The CLEK Study will characterize the relationship between corneal curvature, as measured by keratometry, and each of several pre-defined covariates. The covariates of interest are corneal irregularity, corneal scarring, the patient’s age, whether the patient wears spectacles or contact lenses, and the type of contact lens worn. 2.2.4 Specific Aim D. Factors Related to Corneal Scarring The CLEK Study will determine the relationship between corneal scarring, measured by a standardized photography and reading method, and each of several predefined covariates. The covariates of interest are corneal curvature, the patient’s age, high and low contrast best corrected and 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. It is expected that the results of these four sets of evaluations, and the relationship between those results will lead to a better understanding of the clinical course of keratoconus and will provide the framework for new approaches to the management of keratoconus. 2.3 Rationale for Observational Study The CLEK Study Executive Committee has considered the recommendations of the National Eye Institute’s Vision Research Review Committee and has concurred that a clinical trial of contact lens fitting methods in keratoconus is premature, primarily because of the many things that are unknown about keratoconus. Data required for assumptions key to the planning and design of the clinical trial are absent, eg, the proportion of patients exhibiting visual acuity loss of clinically important magnitude, the proportion of keratoconus patients who experience contact lens intolerance, and the incidence of corneal scarring. These data are required to provide a sound basis for estimating proposed clinical trial outcome measures such as visual acuity loss, decrease in contact lens wearing time, and the occurrence of corneal scarring. Unfortunately, these variables have not been systematically studied in this population. An
2/1/99 Chapter 2 Study Design page 2-4 observational study addresses these deficiencies in our understanding of keratoconus and its course. Following the second study section review of the clinical trial and based on the reviewers’ recommendations, the CLEK Executive Committee conducted a survey in fall 1993 of all CLEK Study investigators involved in the pilot screening study. The 32 respondents (29 optometrists, 10 of whom are practicing or have practiced in ophthalmologic settings, and 3 ophthalmologists/cornea specialists) classified 10 areas of potential study in keratoconus as to their importance. Disease progression, etiology, and corneal scarring were considered very important to study by 81%, 72%, and 63% of the respondents respectively. Other high-ranking areas were corneal topography, the best method for fitting contact lenses, and visual acuity. The survey results and a subsequent series of conference calls to discuss these issues with the original clinical trial clinic investigators led the CLEK Executive Committee to the conclusion that there are important unanswered questions in keratoconus that should be studied before attempting to conduct a clinical trial of optical management methods, namely to fully describe keratoconus in the areas of its effect on vision, its progression, and its accompanying corneal changes. The need for such an observational study is underscored by recommendations from the VRRC’s two summary statements and by the recommendation of the National Advisory Eye Council in September 1993 on a previous proposal for a randomized clinical trial in keratoconus patients. The initial summary statement, from the October/November 1992 review, emphasized disease progression, stating, “Most of all, [the reviewers] felt that disease progression should be the primary focus.” Further, they identified specific parameters that should be evaluated to describe progression in keratoconus, namely, “in lens-wearing keratoconus patients, changes in visual acuity ... and lens fit are good clinical indicators of progression of keratoconus.... Given the expense of this study [the previously proposed randomized clinical trial], it seems a shame that the more important question of disease progression will not be evaluated.” These same reviewers identified a strength of the study, a randomized clinical trial, as “the development of a patient base for longitudinal studies in this population.” The second summary statement, from June 1993, called for “pilot data supporting the validity of the principal hypothesis [of the clinical trial] ... and by estimates of the sensitivity of the proposed primary variables [visual acuity loss and contact lens wearing time decrease] in the target population.” They observe that “the natural history and progression of [keratoconus] is very poorly documented. This is particularly true in patients who are not wearing contact lenses, since rather few patients go through a complete evolution of the disease process in the absence of contact lens intervention.” A more detailed request for pilot data noted, “No data was provided from trial studies of the likelihood of participants losing two lines of vision or failing to wear their contact lenses for at least ten hours a day.” Further, in September 1993 the Council Action sheet from the National Advisory
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