TNF-Alpha Levels in Tears: A Novel Biomarker to Assess the Degree of Diabetic Retinopathy

We assess the level of tumour necrosis factor alpha (TNF-alpha) in tear fluids and other serumparameters associated with diabetes in
different degrees of diabetic retinopathy.We have performed a prospective, nonrandomized, observational study. Study population
consisted of 16 healthy subjects (controls) and 32 type 2 diabetic patients: 16 affected by proliferative diabetic retinopathy (PDR)
and 16 with nonproliferative retinopathy (NDPR, background/preproliferative). Bodymass index, urinary albumin, blood glucose,
HbA1c, and tear levels of TNF-alphawere measured in all subjects.Thevalue of glycaemia, microalbuminurea, and Body mass index
in diabetic retinopathy groups were higher than those in control group ( < 0.05). Glycemia in NPDR: 6.6mmol/L (range: 5.8–
6.3); in PDR: 6.7mmol/L (range: 6.1–7.2); in control: 5.7mmol/L (range: 4.9–6.1); microalbuminurea in NPDR: 10.6mg/L (range:
5.6–20); in PDR: 25.2mg/L (range: 17–40); in control: 5.3mg/L (range: 2.6–10); Body mass index in NPDR: 26 Kg/m2 (range: 20.3–
40); in PDR: 28 Kg/m2 (range 20.3–52); in control: 21Kg/m2 (range 19–26).The TNF-alpha concentrations in tears increase with
the severity of pathology and were lower in control group than in diabetic subjects. In the end, the level of TNF-alpha is highly
correlated with severity of diabetic retinopathy and with nephropathy. Tear fluid collection may be a useful noninvasive method
for the detection of proliferative diabetic retinopathy.