Characteristics of Macular Intra-Retinal and Choroidal Layers in Type 2 Diabetic Patients Studied with Optical Coherence Tomography

Abstract

Objective: To investigate the characteristic changes in the fine structure of the retinal and choroidal layers of type 2 diabetic patients using optical coherence tomography (OCT), and to provide an effective means for the early diagnosis and progress monitoring of diabetic retinopathy (DR). Methods: This case series study included 67 patients with type 2 diabetes at the Second Affiliated Hospital & Yuying Children's Hospital of Wenzhou Medical University from December 2015 to April 2017. The diabetic patients were divided into a diabetic without retinopathy (NDR) group of 40 cases (40 eyes), and a non-proliferative diabetic retinopathy (NPDR) group with 27 cases (32 eyes). In addition, the study enrolled 39 normal subjects (39 eyes) as a control group who were age, gender and refractive-error matched. Using RTVue-OCT, the macular region was scanned in radial mode and the 3D images of the retina and choroid were obtained from all subjects in a 6-mm area of the retina, which was divided into eight intra-layers using custom software. The 6-mm round was divided into three rings, including central, inner, and outer rings and the rings were further divided into nine regions (C, S1, T1, I1, N1, S2, T2, I2 and N2). Thickness data in each region was compared among the three groups by ANOVA. Results: There were no significant differences in the total retinal thicknesses among the three groups. The thickness of the retinal nerve fiber layer (RNFL) decreased in the NDR group in the C, N1, T1 and T2 regions compared to the control group (P<0.05). The membrane of the inner nuclear layer (INL) in the NDR group was thicker in S2 and T2, and it was even thicker in the NPDR group in the N1, I1, S2, T2, I2 and N2 regions (P<0.05) compared to the controls. The layer of the myoid and ellipsoid zone (MEZ) was thinner in the NPDR group compared to the control group in almost all regions except for the center (P<0.05). In addition, the choroid was significantly thinner in the NDR and NPDR groups in all nine areas compared to the control group. Conclusions: OCT can effectively detect the early changes in the fine structures of the macular retinal and choroidal layers. In patients with diabetes, extensive lesions in the choroid layer occur when DR has not been clinically diagnosed. It is speculated that choroidal thickness might be an effective indicator to predict early retinopathy in diabetic patients. Key words: diabetes; macula; intra-retinal layers; choroid; optical coherence tomography