An Investigation of the Effect of Cataract Surgery and Vitrectomy on the Antioxidant Status of the Aqueous Humour and Vitreous Through the Quantification of Glutathione

Abstract

Purpose: : The cumulative effects of oxidative stress in the eye over a lifetime can lead to cataract formation and age-related macular degeneration. Glutathione is an important natural free-radical scavenger in the eye. The goal of the study is to use the ratio of oxidized/total glutathione as a marker for oxidative stress and quantify its presence within the aqueous humor and vitreous of patients with different ocular status such as previous cataract surgery and vitrectomy.

Methods: : Aqueous humor and vitreous samples from sequential subjects set to undergo pre-scheduled eye surgery were collected upon the initiation of the surgical procedure. They were analyzed using reverse-phase high-performance liquid chromatography (RP-HPLC) for the quantitative presence of glutathione.

Results: : There were 56 eyes of 56 patients (31 male and 25 female) in this prospective study. The average age was 65. Thirty-six eyes had no previous surgery. Eight eyes had undergone cataract surgery, 5 eyes had vitrectomy and 7 had a combination of the two. Comparing aqueous samples of oxidized glutathione (GSSG)/total glutathione in eyes with no previous surgery and in vitrectomized eyes, it was 15% and 4% respectively (p=0.02). In 12 cases, samples were taken concurrently from both the aqueous humor (AC) and the vitreous (VH). In these patients, the percentage of GSSG to total glutathione was 43% in VH vs. 19% in AC (p= 0.01). The axial length correlation with the ratio of GSSG/total glutathione was 0.43. Age did not correlate with the oxidized glutathione ratio.

Conclusions: : A higher ratio of oxidized (GSSG) to reduced (GSH) glutathione is an indication of more demand for its role as antioxidant in reducing oxygen radicals and hence of greater exposure to oxidative stress. The vitreous oxidized glutathione ratio is higher than that of the aqueous humor in all our samples. There is also a higher ratio of oxidized to reduced glutathione within the aqueous humor of eyes with no previous surgery compared to vitrectomized eyes. Both findings are surprising given the previous data from oxygen sensor measurements. Possible mechanisms for these findings will be discussed.

Keywords: cataract • oxidation/oxidative or free radical damage • vitreoretinal surgery