Measurement of photoreceptor layer in glaucoma: a spectral-domain optical coherence tomography study

Abstract

Objective. To measure and compare photoreceptor layer thickness between normal and glaucomatous eyes using spectral-domain optical coherence tomography (OCT). Methods. Thirty-eight healthy normal volunteers and 47 glaucoma patients were included in the analysis. One eye from each participant was randomly selected for macula imaging by a spectral-domain OCT (3D OCT-1000, Topcon, Tokyo, Japan). The foveal and parafoveal (1.5 mm from the fovea) outer nuclear layer (ONL) and inner and outer segments (IS+OS) layer thicknesses were measured by a single masked observer. The measurements were repeated 3 times in a random sample of 30 normal eyes to determine the repeatability coefficient and intraclass correlation coefficient. Results. The measurement variabilities of photoreceptor thickness were low. The respective intraclass correlation coefficients of ONL and IS+OS thicknesses were 0.96 (95% confidence interval: 0.94-0.98) and 0.82 (95% confidence interval 0.70-0.90). While there were no differences in parafoveal ONL and IS+OS thicknesses between normal and glaucoma groups (P ≤ .410), the foveal ONL thickness was greater in glaucomatous eyes (P = .011) than in normal eyes. Conclusions. Glaucomatous damage may involve structural change in the photoreceptor layer.

Figure 1

Macular imaging with spectral-domain optical coherence tomography (a). The outer nuclear layer (ONL) thickness is defined as the distance between the posterior boundary of outer plexiform layer and external limiting membrane. The inner and outer segments (IS + OS) are defined as the distance between the external limiting membrane and the RPE. Measurements were obtained at the foveola (b) and 1.5 mm from the fovea (c). OPL: outer plexiform layer; ONL: outer nuclear layer; ELM: external limiting membrane; IS + OS: inner and outer segments; RPE: retinal pigment epithelium.