Correlation of the retinopathy degree with the change of ocular surface and corneal nerve in patients with type 2 diabetes mellitus

AIM: To investigate the change of ocular surface and corneal nerve and their correlation in patients suffering from type 2 diabetes mellitus under different degrees of retinopathy. METHODS: Totally 129 type 2 diabetes mellitus patients (257 eyes) were included. They were divided into three groups: no diabetic retinopathy (NDR) group (33 cases, 66 eyes), non-proliferative diabetic retinopathy (NPDR) group (32 cases, 64 eyes), and proliferative diabetic retinopathy (PDR) group (34 cases, 67 eyes). Healthy normal individuals were enrolled as controls (30 cases, 60 eyes). Ocular Surface Disease Index (OSDI) questionnaire was completed by all subjects, and dry eye analyzer was applied to examine tear meniscus height (TMH), first tear break-up time (FTBUT), average tear break-up time (ATBUT), tear film lipid layer thickness classification, and meibomian gland loss (MGL) score. Corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD), corneal nerve fiber length (CNFL), and corneal nerve fiber tortuosity (CNFT) were examined by in vivo confocal microscopy (IVCM). The differences and correlation among these parameters were analyzed. RESULTS: Total OSDI score, TMH, FTBUT, ATBUT, tear film lipid layer thickness, MGL score, CNFD, CNBD, CNFL, and CNFT were statistically different among the four groups (P<0.05). In NDR group, CNFL was positively correlated with TMH (r=0.493, both P<0.01) and ATBUT (r=0.437, P<0.05). CNFL in NPDR group was positively correlated with TMH (r=0.642, P<0.01) and ATBUT (r=0.6, P<0.01). CNFL in PDR group was positively correlated with TMH (r=0.364, P<0.05) and ATBUT (r=0.589, P<0.01), with low negative correlation with MGL score (r=-0.331, P<0.05). CONCLUSION: With the progression of diabetic retinopathy, TMH, BUT, lipid layer thickness, CNFL, CNFD, and CNBD gradually decreased, while total OSDI score, MGL score, and CNFT increased. CNFL is correlated with TMH and ATBUT in diabetic patients.