Total Protein Concentration and Tumor Necrosis Factor α in Tears of Nonproliferative Diabetic Retinopathy

SIGNIFICANCE: Total protein concentration (TPC) and tumor necrosis factor α (TNF-α) concentration in tears are correlated with severity of retinopathy. However, minimal data are available in the literature for investigating tear TPC and TNF-α concentrations in Asian individuals with different severity of nonproliferative diabetic retinopathy (NPDR).

PURPOSE: This study evaluated differences of TPC and TNF-α concentrations in tears at different severity of NPDR among participants with diabetes in comparison with normal participants.

METHODS: A total of 75 participants were categorized based on Early Treatment for Diabetic Retinopathy Study scale, with 15 participants representing each group, namely, normal, diabetes without retinopathy, mild NPDR, moderate NPDR, and severe NPDR. All participants were screened using McMonnies questionnaire. Refraction was conducted subjectively. Visual acuity was measured using a LogMAR chart. Twenty-five microliters of basal tears was collected using glass capillary tubes. Total protein concentration and TNF-α concentrations were determined using Bradford assay and enzyme-linked immunosorbent assay, respectively.

RESULTS: Mean ± SD age of participants (n = 75) was 57.88 ± 4.71 years, and participants scored equally in McMonnies questionnaire (P = .90). Mean visual acuity was significantly different in severe NPDR (P = .003). Mean tear TPC was significantly lower, and mean tear TNF-α concentration was significantly higher in moderate and severe NPDR (P < .001). Mean ± SD tear TPC and TNF-α concentrations for normal were 7.10 ± 1.53 and 1.39 ± 0.24 pg/mL; for diabetes without retinopathy, 6.37 ± 1.65 and 1.53 ± 0.27 pg/mL; for mild NPDR, 6.32 ± 2.05 and 1.60 ± 0.21 pg/mL; for moderate NPDR, 3.88 ± 1.38 and 1.99 ± 0.05 pg/mL; and for severe NPDR, 3.64 ± 1.26 and 2.21 ± 0.04 pg/mL, respectively. Tear TPC and TNF-α concentrations were significantly correlated (r = -0.50, P < .0001). Visual acuity was significantly correlated with tear TPC (r = -0.236, P = .04) and TNF-α concentrations (r = 0.432, P < .0001).

CONCLUSIONS: This cross-sectional study identified differences in tear TPC and TNF-α concentrations with increasing severity of NPDR.