Quantitative Analysis of Diabetic Macular Ischemia using Optical Coherence Tomography

Abstract

Purpose: Diabetic macular ischemia (DMI), an important category of diabetic retinopathy (DR), contributes to the pathogenesis of diabetic macular edema (DME) and, in severe cases, is a cause of irreversible visual loss in its own right. In this abstract, we analyze the optical coherence tomography (OCT) features of DMI and correlate these findings with visual acuity.

Methods: Clinical and imaging data were collected retrospectively from patients with type 2 diabetes undergoing fluorescein angiography (FA) and OCT. DMI severity was determined from FA image sets according to Early Treatment Diabetic Retinopathy Study (ETDRS) criteria. OCT image sets were obtained using spectral domain OCT (Spectralis, Heidelberg Engineering). Custom image analysis software was used for quantitative analysis. Retinal spaces quantified included retinal nerve fibre layer (RNFL), inner retina, outer retina, and total retina. Subgroup analyses were performed for eyes with DMI but without diabetic macular edema (DME).

Results: 100 patients (100 eyes) met the inclusion criteria for the study. 14.8% of eyes had severe DMI, 6% moderate DMI, 26.1% DMI, 13.6% questionable DMI, and 38.6% had no evidence of DMI. DME, defined as a foveal retinal thickness greater than 275 µm, was present in 48% of eyes. Across all eyes, mean retinal thickness at the fovea was greater in the presence of DMI, and significantly different between all ETDRS-DMI grades (p=0.02). In eyes “without DME” we observed thinning in the outer retinal layer in eyes with DMI (150.4 ± 31.4 μm) compared to eyes without DMI (167.4 ± 18.5 μm, p=0.04). RNFL thinning was associated with an increased FAZ area (r=-0.231, p=0.03), particularly in eyes “without DME”, and in the outer papillomacular quadrant (r=-0.62, p<0.001). Across the entire cohort, retinal thickness was positively correlated with reduced visual acuity (VA) (r=0.52, p=0.001). However, in eyes with DMI but without DME, retinal thickness was negatively correlated with VA (r=-0.37, p=0.004). In these eyes, a negative correlation between VA and RNFL thickness over the papillomacular area was also seen (r=-0.37, p=0.004).

Conclusions: Thinning of the RNFL and outer retina was observed eyes with DMI but without DME. These parameters showed good correlation with VA and may serve as a useful tool for monitoring DMI in clinical practice or future clinical trials.

Keywords: 499 diabetic retinopathy • 550 imaging/image analysis: clinical • 572 ischemia