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Andrew J. Huang, Yu-Ping Han, Ying-Bo Shui, Fang Bai, Carla J. Siegfried, David C. Beebe; Impact of Corneal Endothelial Dysfunctions on Oxygen Levels in Human Eyes. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6457.
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© ARVO (1962-2015); The Authors (2016-present)
Our recent studies revealed steep oxygen gradients in the anterior segment of human eyes in vivo. To further understand oxygen consumption by corneal endothelium and its implications for oxidative stress in the anterior segment, we compared the intraocular oxygen distribution in patients undergoing cataract surgery or endothelial keratoplasty.
Patients undergoing cataract and/or endothelial keratoplasty surgery were recruited under protocol approved by the WU Human Research Protection Office. A flexible Oxylab pO2TM optical oxygen sensor (optode; Oxford Optronix) was introduced into the anterior chamber (AC) via 30-gauge corneal paracentesis. In all patients, pO2 was measured in anterior AC adjacent to central corneal endothelium, mid-AC and AC angle. In pseudophakes or eyes undergoing cataract extraction, pO2 was also measured at anterior lens surface and in posterior chamber (PC; between the lens and peripheral iris).
pO2 measurements in the AC were performed in 24 eyes. In the reference group undergoing cataract surgery only (n=15), average pO2 near the endothelial surface was 21.6 ± 1.4 mmHg (SE). Intermediate levels of pO2 were noted in mid-AC (10.5 ± 1.2 mmHg) and in AC angle (13.0 ± 1.0 mmHg). The pO2 was 3.7 ± 0.9 mmHg near the crystalline lens surface and 4.0 ± 0.8 mmHg in the PC. These findings were consistent with our previous report in eyes undergoing cataract surgery. In the endothelial keratoplasty study group (n=9), there was a significant increase in pO2 near the corneal endothelial surface (40.8 ± 2.4 mmHg, p=1.1x10-5) and a trend toward increase in the mid-AC (19.0 ± 3.8 mmHg, p=0.06). The average endothelial densities were 2494 ± 179 cells/mm2 in the reference and <500 cells/mm2 in the study group. Preoperative central corneal thickness (CCT) was 555 ± 18 µm and 699 ± 32 µm (p=0.004) in the reference and study groups, respectively. A significant correlation was noted between CCT/endothelial density and pO2 at the endothelium (r=0.009 for CCT, 1.84x10-7 for endothelium). No correlations were found with pO2 at AC angle, lens surface or PC.
Our in vivo measurements confirmed the steep oxygen gradients in healthy human eyes. Endothelial dysfunction alters the oxidative environment in the aqueous humor and may play a role in anterior segment pathologies.
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