Retinal thinning in mice with streptozotocin-induced diabetes mellitus

Abstract

Purpose: Inner retinal thinning in humans with type I diabetes mellitus (DM) has been previously described by us and others in eyes with no detectable diabetic retinopathy. We sought to compare retinal topography in vivo of wild type mice to those with diabetes mellitus using the Iowa Reference Algorithm for three-dimensional automated layer segmentation of spectral domain optical coherence tomography (OCT). We also wanted to determine whether similar findings could be replicated with ex vivo histologic ganglion cell analysis.

Methods: C57BL/6 mice (3 months) were assigned into streptozotocin-induced diabetes mellitus (DM; n=20) and age-matched control cohorts (n=10). Retinal OCT imaging was performed (Bioptigen, Morrisville, NC) at baseline, 6 weeks, and 20 weeks after induction of diabetes. Using the Iowa Reference Algorithm, mathematically enhanced for mouse OCT, average change in thickness of the combined retinal nerve fiber layer and ganglion cell layer (RNFL-GCL) and total retinal thickness were quantified and compared using two-tailed paired t-test analysis at 0, 6 weeks, and 20 weeks for each group. To evaluate the histologic characteristics of diabetic mouse retina, immunofluorescence staining were performed. The number of ganglion cells in the RNFL and GCL was determined and averaged in five peripheral regions of each section on either side under light microscopy using 200 magnification.

Results: The mean thickness of RNFL-GCL layer in DM at 20 weeks (6.24μm) was thinner (p<0.05) compared to baseline (8.85μm). The mean total retinal thickness of the DM group at 20 weeks (216.5μm) was similar to the control group (216.2μm). The mean number of ganglion cell measured per ganglion cell layer length (count/μm) in the DM group (0.0148/μm) was less than control group (0.0164/μm; p=0.006).

Conclusions: Significant decrease in inner retinal layer thickness (especially RNFL-GCL) is seen in mice after 6 and 20 weeks of streptozocin-induced diabetes mellitus using both OCT and histologic analysis. These findings suggest that neuroretinal alterations are consistently seen in early and later stages of streptozotocin-induced diabetes.

Keywords: 498 diabetes • 691 retina: proximal (bipolar, amacrine, and ganglion cells) • 551 imaging/image analysis: non-clinical