Purchase this article with an account.
C. J. Siegfried, Y.-B. Shui, M. B. Wilkins, N. M. Holekamp, J. H. Hou, F. Bai, D. C. Beebe; Oxygen Levels and Distribution in the Anterior Chamber: Impact of Cataract Surgery and Vitrectomy. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1671.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Previous studies suggest that oxidative stress plays a role in glaucoma development and that the lens may protect the outflow system from oxidative damage post-vitrectomy (Chang, AJO 2006). To explore the balance of oxidants and anti-oxidants in the anterior segment, we measured levels and distribution of oxygen (pO2) and ascorbic acid (AsA) in patients undergoing intraocular surgery.
Consenting patients undergoing cataract and/or glaucoma surgery were included. An Oxylab pO2TM optical oxygen sensor (Oxford Optronix) was introduced via 30G corneal paracentesis. In all patients, pO2 was sampled in the anterior chamber (AC) angle, mid-AC, and near corneal endothelium. In pseudophakes and eyes undergoing lens extraction, the probe was introduced into the posterior chamber (PC; between lens and peripheral iris) and near the anterior lens surface. Aqueous humor samples were collected and AsA measured by colorimetric analysis.
92 patients participated. In the reference group (eyes undergoing initial surgery), pO2 was highest adjacent to cornea (22.1 ± 1.1 mmHg; ± SE), and decreased in a linear gradient to 3.1 ± 0.4 mmHg near the lens surface. pO2 was also low in the PC (3.8 ± 0.6 mmHg). An intermediate pO2 was measured in the AC angle (13.6 ± 1.0 mmHg). In the subgroup of eyes with prior pars plana vitrectomy scheduled to undergo cataract extraction (n=10), there was a significant increase in pO2 in the PC (6.5 ± 1.0 mmHg; p=0.02) and a trend toward increased oxygen in the AC angle (17.8 ± 4.3 mmHg). A significant increase in pO2 at the anterior lens surface (p=0.002) and in the PC (p=0.038) was noted in pseudophakes. Multivariate analysis revealed a strong correlation of pO2 in the PC and the AC angle in all eyes (p<10-4). A significant inverse relationship (p=0.03) was noted between central corneal thickness (CCT) and AC angle pO2 levels. AsA levels in diabetics were significantly lower than non-diabetics.
These in vivo measurements are the first to define oxygen gradients in the anterior segment of the human eye. The effect of vitrectomy and lens extraction on pO2 levels in the PC and AC angle suggest an important influence of both vitreous and the natural lens in regulating oxygen distribution/metabolism within the eye and provide further evidence for the importance of these structures and of oxygen distribution in the development of glaucoma. The inverse relationship between CCT and pO2 may account for the increased risk of glaucoma in persons with thinner corneas, a previously unexplained association.
This PDF is available to Subscribers Only