Relationship between degree of diabetic retinopathy and changes of corneal sub-basal nerve plexus in the whorl-like region

Objective

To estimate the correlation between DR and diabetic corneal nerve damage by comparing changes of corneal sub-basal nerve plexus (SNP) in the whorl-like region in different DR stages.

Methods

In this cross-sectional study, 66 eyes of 66 type 2 diabetes patients aged 50-65 years old in Shanxi Eye Hospital from September 2018 to January 2019 were included.The subjects were divided into non-diabetic retinopathy group (NDR), non-proliferative diabetic retinopathy group (NPDR) and proliferative diabetic retinopathy group (PDR) accordingly, the right eyes were enrolled.20 eyes of 20 age and gender matched age-related cataract patients were also included as control group.All the subjects underwent confocal corneal microscopy to observe the morphology of SNP in the whorl-like region and measure the nerve fiber length (NFL) in this area.Covariance analysis using disease course as the covariate was used to analyze the differences of NFL value among groups, and Spearman rank correlation analysis was used to analyze the correlation between NFL value and DR stages.The study protocol was approved by the Ethics Committee of Shanxi Eye Hospital.Written informed consent was obtained from each patient prior to entering the study cohort.

Results

The whorl-like region were observed in all the eyes.In the control group, nerve fibers were uniform in thickness, densely distributed with regular course, and most of the tested eyes had intact whorl-like structure.Nerve fibers in different DR groups all showed generally decrease in diameter and density, with increase in tortuosity, accompanied by different degrees of whorl-like structure loss.Eyes in the NDR group and NPDR group mainly showed nerve structure loss in the whorl-like center; while some eyes in the PDR group also showed nerve structure loss in the inferior and temporal of the whorl-like region.The NFL values were (21.08±4.74), (16.47±6.35), (14.95±3.90), and (11.61±3.24)mm/mm² in the control group, the NDR group, the NPDR group, and the PDR group, respectively, the overall difference was statistically significant (F=10.541, P<0.001). The NFL value in the control group was significantly higher than those in the different DR groups, the differences were statistically significant (all at P<0.01). Spearman rank correlation analysis showed that there was a significant negative correlation between NFL value and DR stages (r_s=-0.356, P=0.003).

Conclusions

Diabetic SNP damage occurs earlier than DR, and progress gradually with the development of DR; Different stages of DR are accompanied by different degrees of nerve structure loss; The structure loss begins at the whorl-like center and gradually develops to downward and the temporal side.The ophthalmologists should take the condition of ocular surface into account when treating ocular fundus diseases of diabetic patients.