Decreasing Retinal Layer Thickness with Increasing Diabetes Duration is Independent of Diabetic Retinopathy Severity and Retinal Central Subfield Thickness

Abstract

Purpose: : To evaluate retinal layer thickness differences assessed by segmentation of Spectral Domain optical coherence tomography (SD OCT) images in patients with a wide range of diabetes (DM) duration and diabetic retinopathy (DR) severity level.

Methods: : Subjects with NPDR (N=17) were grouped by ETDRS DR clinical severity and DM duration: short (=<5 yrs, N=8), moderate (20-30 yrs, N=12) and long (>50 yrs, N=6). Thickness maps (20x20^o cube) of the macula and average overall individual retina layer thickness were obtained using Spectralis OCT (Heidelberg Engineering, Germany). Segmentation analysis of retinal layers was performed using a high resolution interactive digital tablet and Matlab software: nerve fiber layer (RNFL), ganglion cell & inner plexiform layers (GCL-IPL), inner nuclear & outer plexiform layers (INL-OPL), outer nuclear layer (ONL), and photoreceptor & RPE layers (Ph-RPE). Manual segmentation correction was applied by experienced graders (average intergrader layer thickness correlation = 0.98).

Results: : Although there was no correlation between center subfield thickness (CST) & DM duration (p=0.21), individual retinal layer thickness decreased with increasing DM duration: GCL-IPL (p<0.0001), NFL (p=0.002), INL-OPL (p<0.001) and ONL (p=0.01). These findings remained statistically significant after multivariable modeling adjusted for age and gender. No significant association was detected between Ph-RPE thickness and DM duration, nor was there a correlation between any retinal layer thickness and DR severity. Total retinal thickness across every individual inner and outer zone on retinal thickness maps decreased with increasing DM duration (all p<0.0001).

Conclusions: : Retinal layer thickness decreased with increasing duration of DM (especially in the inner retinal layers) with little effect on the photoreceptor/RPE layer. The paracentral retina was more affected with increasing DM duration than central subfield thickness. Change in retinal layer thickness was not observed with changing DR severity. Such findings may be important for future studies analyzing paracentral retinal thickness or possible chronic neurodegenerative effects in patients with diabetes.

Keywords: diabetic retinopathy • imaging/image analysis: clinical