RNFL thinning may precede neuroretinal degeneration in diabetics

Thinning of the peripapillary inferior-temporal retinal nerve fibre layer (RNFL) may be an early sign of neuroretinal degeneration in diabetics without diabetic retinopathy (DR), a recent study has found.

Researchers performed a cross-sectional analysis of 95 type 2 diabetics, none of whom had DR. Spectral-domain optical coherence tomography (SD-OCT) was used to measured RNFL thickness. A parallel group of 91 age- and gender-matched nondiabetic controls was also included. Each participant contributed one eye for analysis.

Compared to controls, diabetics had a significantly lower inferior-temporal peripapillary RNFL thickness (p=0.042). No other SD-OCT parameter was significantly different between the two groups.

The mean duration of diabetes was 8.9±5.6 years, and the average concentration of glycated haemoglobin (HbA1c) was 7.1±1.2 percent. Stratifying patients according to HbA1c showed that superior RNFL was thinner in those with HbA1c >7 percent (p=0.049). Other SD-OCT parameters were unaffected by HbA1c.

Moreover, superior, nasal, and temporal perifoveal thickness values were all significantly lower in patients who had diabetes longer than 10 years than in those with shorter disease durations.

Correlation analysis revealed a statistically significant link among age, duration of diabetes, HbA1c, and macular measurements. No such effect was found for peripapillary SD-OCT parameters.

“[E]arly retinal neurodegeneration appears to manifest as peripapillary RNFL thinning on SD-OCT prior to the retinal and generalized vascular deterioration, and it seems to be associated with poor blood glucose control,” researchers said.