Results of this retrospective study should prompt ophthalmologists to carefully evaluate patients with clinical or subclinical peripheral neuropathy or autonomic dysfunction.
Researchers used OCT to evaluate the relationship between retinal thickness and peripheral nerve conduction and autonomic nerve function in diabetic patients. The results showed that peripheral nerve conduction and autonomic nerve function were closely related to the ganglion cell-inner plexiform layer (GC-IPL) thinning, suggesting that a thinner GC-IPL can be an early sign of diabetic neurodegeneration
Though structural and functional degeneration of retinal ganglion cells has been shown to play a part in the development of diabetic retinopathy, the exact pathogenesis remains unclear. Retinal neurodegeneration and diabetic peripheral neuropathy (DPN) are believed to be initiated by similar hyperglycemia-activated pathways. However, DPN onset is difficult to diagnose due to its varied and vague systemic symptoms.
This cross-sectional study enrolled 160 subjects, aged 55 to 75 years, with diabetes without diabetic retinopathy or mild nonproliferative diabetic retinopathy. Parafoveal retinal thickness and GC-IPL thickness were measured in 6 macular regions. Peripheral nerve involvement was assessed with nerve conduction studies in the peroneal and posterior tibial motor and sural nerves. Subjects were divided into 3 groups: no neuropathy, probable neuropathy and definite neuropathy. Using diagnostic criteria of cardiac autonomic neuropathy, the authors evaluated autonomic nerve function, and classified patients as no/mild dysfunction, moderate dysfunction or severe dysfunction.
The authors found that average GC-IPL thickness was significantly lower in subjects categorized as definite neuropathy compared to the probable and no subgroups (75.2 ± 4.2 mm vs 78.8 ± 5.0 and 82.0 ± 5.8 mm, respectively, P=0.002). Similarly, patients with severe autonomic dysfunction showed the lowest mean GC-IPL thickness compared to those with moderate and no/mild dysfunction (76.6 ± 5.9 mm vs 81.8 ± 3.9 and 82.2 ± 6.6 mm, respectively, P=0.005). However, the mean retinal thickness of parafovea (1–3 mm) was not significantly related.
After correcting for other factors, regression modeling confirmed that both measures of peripheral nervous system health were significantly positively correlated with GC-IPL thickness.
The findings of the study suggest that evaluation of GC-IPL thickness is a reliable early predictor for diabetic neuropathy. Due to its retrospective design, this study was not able to investigate changes in the measured variables over time, and unknown factors could have confounded results. The authors plan to conduct a prospective epidemiologic study of retinal neurodegeneration to reveal correlations with possible epigenetic factors such as family, pharmacological and clinical history.