Neurodegeneration of the retina in type 1 diabetic patients

The degeneration of retinal neurons and glial cells has recently been postulated in the pathogenesis of diabetic retinopathy. Optical coherence tomography (OCT) allows to perform qualitative and quantitative measurements of retinal thickness (RT) with identification of individual retinal layers.

We compared RT, retinal nerve fiber layer (RNFL) thickness, and ganglion cell layer (GCL) thickness obtained by OCT in type 1 diabetic patients with and without clinically diagnosed retinopathy.

The study included 77 consecutive patients with type 1 diabetes (39 men, 38 women; median age, 35 years [interquartile range (IQR), 29-42]; median disease duration, 10 years [IQR, 9-14]) and 31 age- and sex-matched controls. We measured RT in the fovea, parafovea, and perifovea, as well as RNFL and GCL thickness. We divided diabetic patients into 2 subgroups, i.e., those with diabetic retinopathy and without retinopathy.

We observed thicker perifoveal retina (P = 0.05), mean RNFL (P = 0.002), inferior RNFL (P <0.0001), and superior and inferior GCL (P = 0.05 and P = 0.04, respectively) in diabetic subjects compared with the control group. We detected retinopathy in 23 diabetic patients (29%). Compared with patients without retinopathy, subjects with retinopathy had thinner parafoveal retina (P = 0.05), mean RNFL (P = 0.002), inferior and nasal RNFL (P = 0.002, P = 0.03), superior (P = 0.05) and inferior GCL (P = 0.006). Significant correlations were found between duration of diabetes and nasal RNFL thickness (r = -0.32, P = 0.004) and parafoveal RT (r = -0.47, P <0.001).

The results might suggest the loss of intraretinal neural tissue in type 1 diabetic patients with retinopathy. Neurodegeneration in diabetic retinopathy is closly associated with disease duration.