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In this prospective three-year longitudinal study, the authors aimed to explore the relation between retinal neurodegenerative changes and vessel closure (VC) in individuals with non-proliferative diabetic retinopathy (NPDR). The participants included 74 individuals with type 2 diabetes, NPDR, and Early Treatment Diabetic Retinopathy Study grades from 10 to 47; one eye per person. An age-matched healthy population of 84 eyes was used as control group. Participants were annually examined by colour fundus photography, spectral domain-optical coherence tomography (SD-OCT) and OCT-angiography (OCTA). VC was assessed by OCTA vessel density maps. SD-OCT segmentations were performed to access central retinal thickness (CRT) and retinal neurodegeneration considered as thinning of the ganglion cell plus inner plexiform layer (GCL + IPL). The results showed that when compared with the healthy control population T2DM individuals presented significantly higher CRT (p=0.010), GCL + IPL thinning (p=0.042), and decreased vessel density at the superficial capillary plexus (SCP) (p<0.001) and full retina (FR) (p=0.001). When looking at changes occurring over the three-year period of follow-up there were statistically significant decreases in GCL + IPL thickness (-0.438μm/year; p=0.038), foveal avascular zone circularity (-0.009; p=0.047), and vessel density in superficial capillary plexus (-0.172mm-1/year; p<0.001), deep capillary plexus (DCP) (-0.350mm-1/year; p<0.001), and FR (-0.182mm-1/year; p<0.001). A statistically significant association was identified between GCL + IPL thinning and decrease in DCP vessel density (β=0.196 [95% confidence interval: 0.037, 0.355], z=2.410, p=0.016), after controlling for age, gender, diabetes duration, HbA1c level, and CRT. The study concluded that retinal neurodegenerative changes show a steady progression during a three-year period of follow-up in eyes with NPDR and appear to be directly associated with progression in decreased vessel density including vascular closure through preferential involvement of the DCP. The results suggest that the vascular component of the retinopathy appears to initiate in the SCP with subsequent preferential involvement of the DCP with retinopathy progression. It was seen that non-proliferative DR initiates signs of damage of the neuronal tissue in the central macula, followed by failure of the microvascular response, resulting in retinal capillary closure, identified in alterations occurring in the foveal avascular zone (FAZ) and involving predominantly the SCP. Afterward, progression of the disease occurs by progressive neurodegenerative changes and involvement of the DCP, which by itself may then contribute to increased ischemic neurodegeneration and thinning of the GCL + IPL. Important conclusions drawn from this longitudinal study showed that signs of neurodegeneration and capillary closure are present since the initial stages of DR and that these alterations progressed over time. Limitations: Small study, OCTA analyses lacked an effective projection removal algorithm and the limited field examined (3mm × 3mm), prevented an evaluation of peripheral regions of the retina.

Association between neurodegeneration and macular perfusion in the progression of diabetic retinopathy: a three-year longitudinal study.
Marquesa IP, Ferreira S, Santosa T, et al.
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Sofia Rokerya

MBBS MRCOphth FRCSI, King's College University Hospital, UK.

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