Predictors of Visual Acuity Loss in Keratoconus

Abstract

Abstract: : Purpose: To identify factors that predict reduced visual acuity in keratoconus patients. Methods: The Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study is a long–term, observational investigation of 1,209 keratoconus patients. This report uses seven years of follow–up from 953 CLEK Study subjects who had penetrating keratoplasty in neither eye at baseline and who provided enough data to compute the slope of the change over time in high– or low–contrast, best–corrected acuity. Outcome measures included the aforementioned slopes and whether the number of visual acuity chart letters correct decreased by 10 letters or more in at least one eye. Results: Subjects were (mean +/– standard deviation) 40.2 +/– 11 years old, 44.4% of them were female, and 71.9% were White. The slope of the change in high– (–0.29 +/– 1.5 letters/year) and low– contrast (–0.58 +/– 1.7) best–corrected acuity over seven years translates into expected seven–year decreases of 2.03 high– and 4.06 low–contrast letters correct. High– and low–contrast decreases of 10 or more letters correct in at least one eye occurred in 19.0% and 30.8% of subjects, respectively. Significant, independent baseline predictors of reduced high–contrast, best–corrected acuity included better acuity, steeper first definite apical clearance lens (FDACL, a measure of corneal curvature), corneal scarring, and fundus abnormalities (all p<0.025). Significant, independent baseline predictors of reduced low–contrast, best–corrected abuity included better acuity, steeper FDACL, and corneal scarring (all p<0.05). Each diopter of increase from baseline FDACL predicted an increased deterioration of 0.49 and 0.63 high– and low–contrast letters correct, respectively. Conclusions: CLEK Study keratoconus patients exhibited a slow but clear decrease in high– and low– contrast best–corrected visual acuity during follow–up, with low contrast acuity deteriorating more rapidly. Better baseline best–corrected visual acuity, steeper corneas, corneal scarring, and fundus abnormalities were predictive of increased acuity decreases.

Keywords: keratoconus • visual acuity • clinical (human) or epidemiologic studies: risk factor assessment