Pure neuroretinal dysfunction in diabetic retinopathy occurring prior to endothelial and vascular damage

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Abstract

Purpose

To search for independent neural damage in type 1 diabetic patients, in the pre-retinopathy stage of diabetic retinopathy (DR), with preserved blood-retinal barrier (BRB) permeability.

Methods

BRB permeability was objectively measured by Vitreous Fluorometry. Neuroretinal function was assessed by standard multifocal electroretinography (mfERG) and by chromatic/achromatic contrast sensitivity (CS) (CCT-Cambridge Research Systems and Frequency Doubling Perimetry-FDT, Zeiss), in a sample of 42 patients (age=26.6±5.3years) with preserved visual acuity (VA), divided into two groups:1.With no clinical signs of DR and normal BRB permeability (n=23eyes; VA=1.11±0.15); 2.With BRB breakdown, with no clinical signs of DR or with mild nonproliferative DR (n=61eyes; VA=1.09±0.15). These data were compared with those obtained in 25 age-matched controls (27.4±5.8years). Non-parametric statistical analysis was performed at a significance level of p<0.05.

Results

Amplitude of neurophysiological responses was significantly decreased in all eccentricity rings in both patients groups, when compared with controls (p<0.0001). Changes in implicit time were also found in cases with preserved BRB (p<0.02). Impaired CS along the main chromatic axes was observed (p<0.03) and achromatic thresholds were also different between controls and both clinical groups (p<0.004). No correlation was found between the BRB permeability and the psychophysical and electrophysiological measurements (group with preserved BRB), confirming a lesion mechanism that is independent from endothelial/vascular changes.

Conclusion

Retinal neuronal changes may occur in type 1 diabetes, independently of the breakdown of the BRB or onset of vasculopathy.

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