A Study of Aqueous Humour Levels of Ascorbate and Uric Acid in Patients Undergoing Cataract Surgery

Abstract

Purpose: : Antioxidants are thought to play a role in the aetiology of cataract disease. High levels of both ascorbic acid and uric acid are found in the aqueous humour of the eye and these may have antioxidant effects and/or provide protection against UV damage. Ascorbic acid levels in these patients have been studied extensively however there is little information in the literature on the levels of uric acid in the aqueous humour of cataract patients.

Methods: : 250 patients undergoing cataract surgery at St Georges Hospital were recruited into the study following informed consent. A food questionnaire was completed prior to surgery and blood and aqueous humour was collected at surgery for measurement of antioxidants by HPLC with electrochemical detection.

Results: : Mean concentrations of ascorbate in the aqueous humour and plasma were 1.42 and 0.039 mmol/L respectively. Uric acid concentrations were 0.097 and 0.35 mmol/l respectively. There was a weak inverse correlation between the aqueous ascorbate and uric acid levels in the aqueous humour but not in plasma. There was a weak positive correlation between the ascorbate intake as assessed by food questionnaire and the plasma ascorbate level but no correlation with aqueous humour ascorbate levels.

Conclusions: : Significant concentrations of uric acid are found in the aqueous humour. Whether or not it has an antioxidant role in cataract disease is the subject of further study. Aqueous levels of ascorbate are relatively independent of ascorbate intake with little increase in aqueous levels (and presumably therefore of antioxidant activity) once a relatively low threshold of ascorbate intake has been achieved.

Keywords: aqueous • antioxidants • cataract