Abstract
Purpose: :
To examine thickness values and correlations of retinal layers in eyes with normal retinae, retinitis pigmentosa (RP), and of patients with multiple sclerosis (MS).
Methods: :
Optical coherence tomography (OCT) scans were acquired from 40 normal subjects, 16 patients with RP without macular edema, and 12 patients with MS and visual complaints. High-resolution horizontal line scan passing through fovea was acquired from one eye of each patient using Spectralis HRA+OCT™. Retinal layers were segmented to allow calculation of average thickness of retinal pigment epithelium (RPE), photoreceptor layer (PRL), bipolar cell layer (BPL), and the combined ganglion cell and nerve fiber layers (GCL-NFL) in 5mm centered on the fovea (C). Spatial changes in layers’ thicknesses and contribution of each layer to full retinal thickness (FRT) were assessed in 0.5mm increments.
Results: :
In normal eyes, FRT of C was 309µm (standard deviation: SD±16) with nearly symmetric distribution on both sides of fovea (N=317µm ±16.5 and T=300µm ±16.6). RPE layer contributed to 11.5% (SD±1.2) of FRT at C, BPL to 11.5%, (SD±1.2), and GCL to 34.7% (SD±1.8). PR layer comprised the biggest contribution in RT (C=54.3% ±2.1) with the highest contribution 0.5mm on each side of foveal center (N0.5=77.3% ±4.2, T0.5=80% ±7.8). In MS, FRT at C was thinner than normal (P<0.05) in 5 patients (42%), 4 other patients (33%) showed significant focal thinning in subfields other than C, and 3 (25%) were within normal limits in all subfields and in all layers. When considering the contribution of individual retinal layers to the FRT at C, GCL-RNFL was thinner than normal in 9 patients (75%), BPL in 4 patients (33%), and PRL in 4 patients (33%) (P<0.05). The loss in retinal thickness was limited to GCL-RNFL in 5 patients (42%) and to PRL in 2 patients (17%). In RP, FRT, PRL, and RPE at C were thinner than normal (P<0.05) in 7 patients (44%), 4 other patients (25%) showed significant focal thinning of the same layers in the other subfields, and 5 (31%) did not show thinning of any layer. When considering the contribution of PRL to FRT, PRL was significantly thinner than normal in all subfields and in all patients.
Conclusions: :
The wide range of normal retinal thickness may mask structural damage of individual retinal layers in RP and MS. Contribution of individual retinal layers to the full thickness of the retina is more sensitive parameter in assessment of such degenerative diseases, which may enable early detection and subtle changes over time. Our results quatitively confirm previous reports about loss of PR being the hallmark of RP and show that thinning of GCL-NFL is the most observed damage in MS followed by PRL and BPL.
Keywords: imaging/image analysis: clinical • retinal degenerations: hereditary • photoreceptors