Vitamin C levels in human tears.

Human tears, collected using the Schirmer strip method, were analyzed by high-performance liquid chromatography for vitamin C (ascorbic acid). In "basal" tears, the levels of ascorbic acid ranged from 3.9 to 23 mg/dL (220 to 1310 mumol/L); lower values correlated with higher tear flow rates. In reflex tears, induced by brief ammonia inhalation, the ascorbic acid level fell dramatically and appeared to reach a minimum level around 2 mg/dL (110 mumol/L). Even the low level in reflex tears, however, was consistently higher than plasma levels. Ascorbic acid in tears has a potential anti-inflammatory role.