Retinal neurodegenerative changes may develop independent from corneal nerve changes in diabetic retinopathy (DR) patients, a study in the American Journal of Ophthalmology reports. The Australian research team looked at the extent of retinal and corneal neurodegeneration in type 2 diabetes patients and the association with intra-epidermal neuronal loss and diabetic peripheral neuropathy.

The investigation found corneal and intra-epidermal neuronal loss was more pronounced in advanced DR stages, indicating a positive severity correlation between DR and diabetic peripheral neuropathy.

The single-center investigation enrolled 94 type 2 diabetes patients (157 eyes) and placed them into three groups: no DR (68 patients), non-proliferative (48 patients) and proliferative DR (41 patients). Investigators used OCT and confocal microscopy imaging to measure macular and peripapillary neuroretinal layer thicknesses and corneal nerve length/density. Additionally, they performed distal leg skin punch biopsies and generated two neurological scores to determine intra-epidermal nerve fiber density and clinical diabetic peripheral neuropathy.

Among the neuroretinal layers, only the peripapillary retinal nerve fiber layer was decreased in proliferative DR (96μm) compared with the no DR group (103μm)—and only after excluding outliers.

The corneal nerves, however, were far more sensitive to DR changes. The study reported corneal nerve fiber length and density were significantly reduced in both DR groups compared with the no DR patients and moreso in the proliferative DR group than the non-proliferative DR group.

The investigators also reported the intra-epidermal nerve fiber density was statistically significantly reduced in the non-proliferative and proliferative DR eyes compared with eyes without DR.

The study noted a low correlation of intra-epidermal and corneal fiber loss for both neurological scores.

Hafner J, Zadrazil M, Grisold A, et al. Retinal and corneal neurodegeneration and its association to systemic signs of peripheral neuropathy in type 2 diabetes. Am J Opthalmol. September 19, 2019. [Epub ahead of print].