Outer retinal layers as predictors of visual acuity in retinitis pigmentosa: a cross-sectional study

Abstract

Purpose: To evaluate the integrity of the outer retinal layers-outer nuclear layer (ONL), external limiting membrane (ELM), ellipsoid (EZ), and interdigitation band (IZ)-using spectral-domain optical coherence tomography and estimate their effect on visual acuity in retinitis pigmentosa (RP).

Methods: A cross-sectional study was performed in the Ophthalmology Department of Hospital de Braga, Portugal. Patients with RP followed in the Hospital de Braga during January to August 2017 were included. Exclusion criteria were lack of data, macular edema due to RP, and concomitant retinal, optic nerve, or corneal disease that could interfere with visual acuity. Age, sex, time from diagnosis, phakic status, ONL thickness, and presence or absence of foveal ELM, EZ, and IZ were correlated to the best-corrected visual acuity (BCVA).

Results: Forty-eight eyes were analyzed. There was a strong and positive correlation in BCVA between both eyes (p < .001*). ONL thickness was decreased in 95.8%. The EZ was the most absent layer (79.2%), followed by IZ (70.8%) and ELM (45.8%). A positive family history (p = .04*) and increased time from diagnosis (p = .037*) correlated with worse BCVA. A thicker ONL (p = .001*) and the presence of subfoveal ELM (p < .001*), EZ (p < .001*), and IZ (p = .02*) are correlated with better BCVA. There was a strong and positive correlation between the number of layers affected and a lower BCVA (p < .001). The presence of EZ was a significant predictor of BCVA (p = .02*).

Conclusions: The status of the outer retinal layers seems to influence BCVA. The status of the EZ was the most important predictor of BCVA but the ONL, ELM, and IZ may have a cumulative effect in the progression of visual loss.

Keywords: Ellipsoid band; External limiting membrane; Interdigitation band; Outer nuclear layer; Retinitis pigmentosa; SD-OCT.