Purpose: To establish the normal short-term range of variation in the measurement of visual acuity in patients with retinitis pigmentosa.
Methods: Sixteen patients (31 eyes) with retinitis pigmentosa, whose visual acuity ranged from 20/25 to 20/200, participated in this prospective clinical study. The best-corrected visual acuity in undilated and in dilated conditions was recorded independently by two masked observers on two visits of each patient within a 2-week interval by means of the Early Treatment Diabetic Retinopathy Study charts (The Lighthouse, Long Island City, NY).
Results: Using mixed-model analysis, a reasonable upperbound for intervisit (intraobserver) variability of 6.0 letters for the visual acuity of patients with undilated pupils and 6.3 letters for the visual acuity of patients with dilated pupils and the corresponding maximum interobserver variability of visual acuity of 5.7 letters in patients with either undilated or dilated pupils on the Early Treatment Diabetic Retinopathy Study charts were computed. The overall average interobserver and intraobserver variability in visual acuity ranged from 1.3-2.3 letters.
Conclusions: A change in visual acuity of seven letters or more on the standardized Early Treatment Diabetic Retinopathy Study charts may be considered important in patients with retinitis pigmentosa. For these patients with minor lens opacity, visual acuity measurements obtained with undilated and dilated pupils were similar. These findings help to establish guidelines for monitoring the response of visual acuity during any future therapeutic intervention trials or for determining substantial changes in visual acuity over time when the course of visual acuity loss in such patients is monitored.