Retinal thickness profile of individuals with diabetes

To examine the retinal thickness profiles of individuals with and without diabetic retinopathy (DR).

Full retinal thickness in the central zone, overall and hemisphere thicknesses of the parafovea and perifovea, ganglion cell complex (GCC) thickness and retinal nerve fibre layer (RNFL) thickness were assessed in 185 individuals using spectral domain optical coherence tomography (88 individuals with diabetes but no DR, 55 with DR, and 42 non-diabetic controls). The DR group comprised of 60% of participants with very mild non-proliferative diabetic retinopathy (NPDR) (representing microaneurysms only) and 40% with mild NPDR (hard exudates, cotton-wool spots, and/or mild retinal haemorrhages). Regression analysis was performed to determine the factors associated with retinal tissue thickness, taking into account, age, sex, presence of DR, duration of diabetes, HbA1c levels and type of diabetes.

The mean (S.D.) of the overall parafoveal thickness was 306 (16) in the DR group and 314 (14) in the control group (p = 0.02). The mean (S.D.) of the superior hemisphere parafoveal thickness was 309 (16) in the DR group and 318 (14) in the control group (p = 0.02). The mean (S.D.) of the inferior hemisphere parafoveal thickness was 303 (17) in the DR group and 311 (15) in the control group (p = 0.02). There were no significant differences in retinal thickness between groups in the central zone (p = 0.27) or perifovea (p > 0.41). Neither the overall nor the hemisphere RNFL (p > 0.75) and GCC thickness (p > 0.37) were significantly different between the groups. Regression analysis revealed that parafoveal thickness in diabetic individuals was reduced in association with presence of DR (B = -5.9 μm, p = 0.02) and with advancing age (B = -4.5 μm, p = 0.004, for every 10 year increase in age) when adjusted for sex, duration of diabetes, HbA1c levels and type of diabetes.

The inner macula is thinner in the presence of clinical signs of diabetic retinopathy and is compounded by advancing age. The influence of any macular oedema or that by cotton-wool spots could not be ruled out and may still confound these results.