The association between visual acuity and central retinal thickness in retinitis pigmentosa

PURPOSE. To determine whether visual acuity is related to central retinal thickness in patients with retinitis pigmentosa. METHODS. Visual acuities were measured with Early Treatment Diabetic Retinopathy Study (ETDRS) charts and optical coherence tomography (OCT3) was used to calculate retinal thicknesses and grade third high-reflectance bands in 162 patients with the typical forms of retinitis pigmentosa who had Snellen visual acuities of 20/20 to 20/200, minimal to no cataracts, and no visible macular cysts. Sixty-five patients were retested within 2 months to estimate the intervisit variability of retinal thickness measurements. RESULTS. ETDRS acuity was best related to retinal thickness measured at fixation and as the average value over the central 1 mm by a second-order polynomial (r(2) = 0.38 and P < 0.001 in both cases). Acuity was maximal for intermediate retinal thickness and appeared to decline for both lesser and greater retinal thicknesses. By linear regression, the decline in acuity for decreasing retinal thickness was steeper in eyes with an absent third high-reflectance band than for eyes with a partially distinct band. No decline was noted in eyes with an intact band. Assessment of intervisit variability of retinal thickness measurements showed 98% confidence limits of +/- 17 mu m at fixation and +/- 11 mu m for the central 1 mm. CONCLUSIONS. Both retinal thinning ( due to cell loss) and retinal thickening ( due to presumed edema) appear to be associated with lower visual acuity in patients with typical retinitis pigmentosa. The definition of the OCT third high-reflectance band may help to predict which patients are more likely to lose visual acuity as retinal thickness declines. An increase or decrease in retinal thickness of more than 17 mu m at fixation or 11 mu m over the central 1 mm at follow-up can be considered a significant ( P < 0.01) change in these patients.