Serum and tear levels of nerve growth factor in diabetic retinopathy patients

PURPOSE: To measure serum and tear nerve growth factor (NGF) concentrations in diabetic retinopathy (DR) patients to determine whether the NGF correlated with parameters associated with DR. DESIGN: Cross-sectional comparative study. METHODS: The study enrolled 254 DR patients and 71 nondiabetic controls. Patient demographic characteristics and diabetic parameters, including blood sugar levels, HbA1c, liver and renal function, were evaluated in two separate university hospitals. Serum and tear NGF concentrations and the ratio of NGF to total protein (TP) in serum and tear fluid were determined. RESULTS: Serum and tear NGF levels were found to be higher in proliferative diabetic retinopathy (PDR) patients (98.7 +/- 12.1 ng/ml in serum, 45.6 +/- 6.3 ng/ml in tear) than in nondiabetic controls (18.5 +/- 6.1 ng/ml in serum and 8.3 +/- 4.7 ng/ml in tear) and nonproliferative diabetic retinopathy (NPDR) patients (26.6 +/- 5.1 ng/ml in serum and 8.6 +/- 4.2 ng/ml in tear; p < .001 for both serum and tear differences). Similarly, NGF levels were higher in PDR patients than in controls and NPDR patients after adjusting for possible confounding factors such as age, gender, serum blood urea nitrogen, creatinine, and diabetic parameters. In addition, the NGF-to-TP ratio for both serum and tear fluid was higher in the PDR group compared with the control and NPDR groups. NGF levels correlated well with diabetes duration, HbA1c, and blood sugar levels and diabetic nephropathy. CONCLUSIONS: NGF concentration may be a good parameter for evaluating DR status. In addition, serum and tear NGF concentrations correlated strongly, indicating that tear fluid assays may offer an effective, accurate, and noninvasive option for NGF measurement.