Visual sensitivity loss in the central 30° of visual field is associated with diabetic peripheral neuropathy

Abstract

Impaired central vision has been shown to predict diabetic peripheral neuropathy (DPN). Several studies have demonstrated diffuse retinal neurodegenerative changes in diabetic patients prior to retinopathy development, raising the prospect that non-central vision may also be compromised by primary neural damage. We hypothesise that type 2 diabetic patients with DPN exhibit visual sensitivity loss in a distinctive pattern across the visual field, compared with a control group of type 2 diabetic patients without DPN. Increment light sensitivity was measured by standard perimetry in the central 30° of visual field for two age-matched groups of type 2 diabetic patients, with and without neuropathy (n = 40/30). Neuropathy status was assigned using the neuropathy disability score. Mean visual sensitivity values were calculated globally, for each quadrant and for three eccentricities (0-10°, 11-20° and 21-30°). Data were analysed using a generalised additive mixed model (GAMM). Global and quadrant between-group visual sensitivity mean differences were marginally but consistently lower (by about 1dB) in the neuropathy cohort compared with controls. Between-group mean differences increased from 0.36 to 1.81dB with increasing eccentricity. GAMM analysis, after adjustment for age, showed these differences to be significant beyond 15° eccentricity and monotonically increasing. Retinopathy levels and disease duration were not significant factors within the model (p = 0.90). Visual sensitivity reduces disproportionately with increasing eccentricity in type 2 diabetic patients with peripheral neuropathy. This sensitivity reduction within the central 30° of visual field may be indicative of more consequential loss in the far periphery.