Study of early retinal damage in patients with impaired glucose tolerance and type 2 diabetes mellitus

Abstract

Objective To evaluate the effect of early damage to the retina caused by impaired glucose tolerance (IGT) by studying the changes in visual function and the retinal nerve fiber layer (RNFL). Methods This was a cross-sectional study. Patients who visited Cangzhou Center Hospital from June 2012 to 2013 were randomly selected to be assigned to 3 groups: the diabetes mellitus (DM) group (76 patients with type 2 diabetes mellitus for 10 to 20 years without diabetic retinopathy), the IGT group (79 patients with IGT for 3 or more years who have not yet progressed to DM) and a normal control group (80 healthy people). All groups underwent optical coherence tomography (OCT), contrast sensitivity (CS), visual acuity tests, and ophthalmoscope examination. In the DM group, patients were further checked by FFA. Differences in these results, including RNFL thickness of the optic disk and CS measurements, were statistically compared between the different groups (one-way ANOVA). In addition , the correlation of RNFL thickness and CS measurements were analyzed. Results The RNFL thicknesses of patients in the DM group were much lower than in the normal controls in an average 360° circumference (98.3±10.3,P<0.01) , in the quadrant above the optic disk (114.8±14.7,P<0.01) , beneath the optic disk (128.5±15.4,P<0.01) and in the nasal quadrant (71.4±8.6,P<0.05). No significant difference was found between the IGT group and normal control group. At the same time, there was a significant difference in CS measurements between the DM group and normal controls, including patients in their 40s at 6 c/d, 12 c/d and 18 c/d (P<0.01), in their 50s at 3 c/d, 6 c/d, 12 c/d and 18 c/d (P<0.05), and in their 60s and 70s at 3 c/d, 6 c/d, 12 c/d, and 18 c/d (P<0.05). Obvious differences were found in the IGT group for patients in their 40s at 12 c/d and 18 c/d (P<0.05), in their 50s at 6 c/d, 12 c/d and 18 c/d (P<0.05) and in their 60s and 70s at 6 c/d and 12 c/d (P<0.05). There was also a positive correlation between CS measurements at the intermediate frequency (6 c/d) and the average RNFL thickness (r=0.596,P<0.01). Conclusion Results of the present study show that a thinner RNFL and visual dysfunction appear before significant microangiopathy in the retina of type 2 DM patients. Visual function decreases in steps in patients with IGT, and this occurs earlier than a thinning of the RNFL. Key words: Diabetic retinopathy; Impaired glucose tolerance; Preclinical phase; Nerve fiber layer; Tomography, optical coherence; Contrast sensitivity