Early retinal neurodegeneration in preclinical diabetic retinopathy: a multifactorial investigation

Background/Objectives: To investigate effects of microalbuminuria (MA), diabetes duration, glycosylated haemoglobin (HbA1c) level, hypertension (HT) and/or hyperlipidaemia (HL) coexistence on retinal layers in diabetic patients without diabetic retinopathy (DR) using spectral-domain optical coherence tomography (SD-OCT). Subjects/Methods: This cross-sectional study involved 95 (45 had MA and 50 had no MA) patients with type 2 diabetes mellitus (DM) without DR and 91 age- and gender-matched non-diabetic controls. Macular and peripapillary SD-OCT measurements (Heidelberg Engineering GmbH, Heidelberg, Germany), DM duration, HbA1c levels and presence of HT and/or HL were used for statistical analyses. Results: The MA (+), MA (−) and control groups had similar age and gender distribution (p > 0.05). The differences in SD-OCT measurements among the MA (+), MA (−) and control groups were insignificant (p > 0.05). However, diabetic patients (n = 95) had significantly thinner inferior-temporal peripapillary retinal nerve fibre layer (RNFL) (p = 0.042) than in the controls (n = 91). Superior peripapillary RNFL was significantly thinner in patients with an HbA1c level > 7% (p = 0.049). However, 3 mm-nasal, temporal and superior perifoveal thicknesses were significantly lower in patients with DM duration over 10 years (p < 0.05). HT and/or HL coexistence did not lead a significant difference in SD-OCT parameters among the groups. Conclusions: In diabetic patients without DR, peripapillary inferior-temporal RNFL thinning might be an early sign of neuroretinal degeneration and it seems to be independent from vascular endothelial damage (MA). Poor metabolic control appears to lead superior peripapillary RNFL thinning, while perifoveal thicknesses tend to decrease with longer DM duration. © 2019, The Author(s), under exclusive licence to The Royal College of Ophthalmologists