Correlation between corneal and retinal neurodegenerative changes and their association with microvascular perfusion in type II diabetes

PURPOSE: The pathophysiology of diabetic neurodegeneration and microvasculopathy remains controversial. Neurosensory layer thickness and corneal nerve fibre loss represent potential biomarkers of neuropathy. The purpose of this cross-sectional study was to determine the correlation between these neurodegenerative features and their association with retinal microvascular integrity in patients with type II diabetes without retinopathy. METHODS: Nerve fibre length (NFL), density (NFD) and branch density (NBD) were assessed using corneal confocal microscopy. Spectralis optical coherence tomography (OCT) was used for peripapillary retinal nerve fibre layer (RNFL), and macular RNFL, ganglion cell (GCL), inner plexiform (IPL) and inner nuclear layer (INL) thicknesses. Parafoveal vessel density (PVD) was determined using OCT angiography. RESULTS: We analysed 118 eyes of 61 patients. Peripapillary RNFL, macular RNFL, GCL, IPL and INL were 101 ± 8, 29 ± 3, 43 ± 4, 36 ± 3 and 36 ± 3 μm. NFL, NFD and NBD were 12.3 ± 4.4 mm/mm2 , 17.8 ± 7.4/mm2 and 26.7 ± 15.2/mm2 . Corneal nerve fibre variables were neither associated with inner retinal thicknesses nor PVD. A significant positive correlation was found between macular GCL, IPL and peripapillary RNFL with deep capillary plexus PVD (p ≤ 0.05). CONCLUSION: Our results indicate that corneal and retinal neurodegeneration are independent changes early in type II diabetes and that distinct retinal, but not corneal neurodegenerative features, are associated with retinal microvascular perfusion.