|Title||REPEATABILITY OF VISUAL ACUITY MEASUREMENT IN KERATOCONUS|
|Author, Co-Author||Karla Zadnik, Larry Davis, Timothy McMahon, Julie Schornack, Mae Gordon, The Study Group|
Southern Hem III
|Abstract|| PURPOSE. The Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study is an observational study designed to document the progression of keratoconus across the course of the disease. We believe that measurement repeatability must be evaluated in the specific context of a new study as these estimates can have a marked impact on sample size. In particular, the repeatability of visual acuity measurement in a disease such as keratoconus, in which vision is often unstable, is undocumented.
METHODS. The CLEK Study's visual acuity measurement methods were evaluated for their keratoconus-specific repeatability at 15 Participating Clinics across the US. One hundred nine of the 1,210 enrolled CLEK Study patients were seen for a Repeat Visit at their Participating Clinic with either their original clinician or a different clinician. The patients underwent the full battery of tests included in the CLEK Study examination at both the Baseline and Repeat Visits, including Bailey-Lovie high and low contrast visual acuity measured with the patients' habitual correction and high contrast visual acuity measured with the manifest refraction in place.
RESULTS. Entrance high contrast visual acuity, performed with the patient's habitual correction, showed an absolute mean difference of 5.2 letters +/- 6.0 (sd)) with an intraclass correlation coefficient of 0.826. Low contrast acuity at entrance showed an absolute mean difference of 6.0 ± 6.0 letters with an intraclass correlation coefficient of 0.818. High contrast visual acuity with manifest refraction showed an absolute mean difference of 7.00 ± 6.30 letters with an intraclass correlation of 0.844 coefficient.
CONCLUSIONS. We have shown repeatability of visual acuity measurement to be reasonable in the context of a longitudinal study of keratoconus patients. Supported by NIH-NEI grants U10 EY10419, EY10069, and EY10077.
|Affiliation of Co-Authors||The Ohio State University College of Optometry, University of Missouri-St. Louis School of Optometry, University of Illinois-Chicago Department of Ophthalmology, Southern California College of Optometry, Washington University Medical School|