In vivo characterization of ischemic retina in diabetic retinopathy

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Abstract
Objective: The aim of this article is to characterize pathomorphologic changes within particular layers of fluorescein angiographically 'ischemic' compared to 'nonischemic' retina in patients with diabetic retinopathy. Methods: Cross-sectional images of ischemic retinal areas were obtained using Heidelberg Spectralis optical coherence tomography (OCT). Presumed retinal ischemia was defined as focal hypofluorescence in early or early and late phase fluorescein angiography. Pathomorphologic changes on OCT were evaluated and the thickness of retinal layers measured and compared with nonischemic retina at corresponding topographic locations in a matched-pairs design based on 22 eyes (mean age 64 ± 14). Results: In all eyes, based on spectral domain-OCT cross-section images, the retina layers in ischemic retinal areas could be segmented. Total retinal thickness was significantly increased in ischemic compared to nonischemic areas (381 ± 94 µm versus 323 ± 89 µm, P = 0.005). Middle retinal layers (inner nuclear layer, outer plexiform layer, and outer nuclear layer) were significantly thickened in retinal ischemic areas (215 ± 82 µm versus 168 ± 62 µm, P = 0.002). The inner retinal layers (retinal nerve fiber layer, ganglion cell layer, and inner plexiform layer) showed a nonsignificant change (117 ± 53 µm versus 98 ± 30 µm), while the outer layers were slightly thinned (photoreceptors plus retinal pigment epithelium layer; 51 ± 9 µm versus 57 ± 8 µm, P = 0.02) in ischemic versus nonischemic retina. Conclusions: Ischemic diabetic retina seems to be thickened due to thickening of, in particular, middle retinal layers, which can be measured with high-resolution OCT.

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