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C. J. Siegfried, Y. B. Shui, M. A. Wilkins, D. C. Beebe; Oxidant Distribution and Antioxidant Protection in Patients With Glaucoma and Cataract. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1575.
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© ARVO (1962-2015); The Authors (2016-present)
Previous studies suggest oxidative stress plays a role in development of both cataract and glaucoma. To further our understanding of the balance of oxidation control in the anterior chamber (AC), we are measuring the levels and distribution of selected oxidants and antioxidants in patients undergoing intraocular surgery.
Cataract and/or glaucoma surgical patients were recruited from an academic glaucoma practice following protocol approval by the Human Research Protection Office. Cataracts were graded preoperatively using the Lens Opacities Classification System III. To map oxygen levels in the anterior chamber, an Oxylab pO2TM optical oxygen sensor was introduced via a 30-gauge needle corneal paracentesis. In all patients, pO2 was sampled in the AC angle, in mid-AC, and near corneal endothelium. In pseudophakic patients or those undergoing cataract extraction, the probe was also introduced into the posterior chamber (between lens and peripheral iris) and just anterior to the lens surface. Aqueous humor (AH) samples were collected and analyzed for ascorbic acid (AsA) and hydrogen peroxide (H2O2) by colorimetric, electrochemical and gas chromatography/mass spectrometry (GC/MS).
In this initial study, 28 patients underwent pO2 measurements in the AC. pO2 was highest adjacent to the cornea (24.8 ± 7.6 mmHg;± SD), decreasing to 4.7 ± 2.6 mmHg near the lens. Oxygen levels were also low in the posterior chamber (5.0 ± 3.2 mmHg). Intermediate levels of pO2 occurred in the mid-AC (13.4 ± 4.0 mmHg) and in the AC angle (13.0 ± 6.2 mmHg), with the greatest absolute variation in the angle. In these preliminary data, no significant differences were detected between cataract and glaucoma patients. Our preliminary data revealed compounds in AH that interfered with colorimetric measurement of H2O2, suggesting that previous colorimetric measurement of H2O2 in AH may have been unreliable. AH analysis for AsA by colorimetric and GC/MS methods and for H2O2 by electrochemical methods are in process.
Our in vivo measurements provide the first comprehensive description of oxygen gradients in the human eye. The pO2 at the anterior surface of the lens and in the posterior chamber were substantially lower than those found in other species. The marked decrease of pO2 and greater variability in the AC angle, compared to the central cornea, suggest different factors affect oxygen levels in these locations. Determination of AsA and H2O2 levels, rates of O2 consumption by AH and the relationship of these factors in patients with cataract and glaucoma is in progress.
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