Are Single Measurements of Antioxidant Activity in the Aqueous Humour of the Eye Meaningful?

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. It is not known to what extent these concentrations fluctuate over time and therefore it is difficult to gauge the significance of assays of single samples taken at the time of cataract surgery.

Methods: : As part of a larger study involving 250 individuals, 16 patients underwent cataract surgery on their second eye in the same unit and under the same surgeon (GT) as for the first. Blood and aqueous humour ascorbate and uric acid were measured on both occasions and many patients completed a second food questionnaire. Ascorbate and uric acid levels were measured by HPLC with electrochemical detection.

Results: : There was a high correlation between the ascorbate (R=0.84) and uric acid levels (R=0.77) of the first and second eye for each patient even though the time interval between operations was up to 12 months. The results of the food questionnaires (n=12) were also highly correlated for most patients (R=0.6 or 0.94 after removal of two outliers). For the small number where a significant difference was found it was not possible to determine whether this was due to seasonal variation or the impact of changing health or vision during the interval between the two operations.

Conclusions: : Aqueous humour levels of ascorbate and uric acid remain relatively unchanged over periods of up to 12 months in most cataract patients indicating that single point measurements of these antioxidants in the aqueous humour is probably a valid measure of that individuals aqueous humour antioxidant status.

Keywords: aqueous • antioxidants • cataract