Ascorbic acid concentration and total antioxidant activity of human tear fluid measured using the FRASC assay

PURPOSE. TO evaluate a novel method (FRASC) for total ferric reducing (anti oxidant) activity and ascorbic acid concentration applied to human tears, t o investigate the stability of ascorbic acid, and to determine the antioxid ant status of human reflex tears. METHODs. Linearity, sensitivity, and precision of FRASC and ascorbic acid l oss during 7 days' storage were assessed; total antioxidant activity and as corbic acid and uric acid concentrations of reflex tears from 47 healthy su bjects were measured. RESULTS. FRASC has good precision, linearity, and sensitivity. Ascorbic aci d is stable for at least 7 days at moderately acidic pH (pH 3.6) and low te mperature. Total antioxidant activity and ascorbic acid and uric acid conce ntrations (mean +/- SD) in reflex tears were 409 +/- 162, 23 +/- 9.6, and 6 8 +/- 46 mu M, respectively. Ascorbic acid and uric acid constituted around half the total antioxidant activity measured. There was a significant corr elation between uric acid and total antioxidant activity (r = 0.754; P < 0. 0001). Men had significantly (P = 0.0045) higher tear ascorbic acid concent rations than women. CONCLUSIONS. FRASC is suitable for measuring total antioxidant activity and ascorbic acid in human tears. Further clinical study is needed to investig ate the male-female difference seen, to characterize the remaining 50% anti oxidant activity, and to investigate the effects of environmental condition s, antioxidant supplementation, age, and ocular disease on tear antioxidant status.