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Y.-B. Shui, C. J. Siegfried, N. M. Holekamp, M. A. Wilkins, F. Bai, J. Hou, D. C. Beebe; Oxygen Levels Around the Human Lens and Alteration After Vitrectomy or Cataract Surgery. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2542.
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Loss of the hypoxic environment around the human lens increases the risk of nuclear cataracts. Our previous study found that vitrectomy increased oxygen levels in the posterior segment. We report in vivo measurements of oxygen distribution in the anterior segment of the human eye prior to and following vitrectomy or cataract surgery.
Consenting patients undergoing vitrectomy, cataract and/or glaucoma surgery were enrolled. Oxygen measurements were made at the beginning of surgery using an Oxylab pO2TM optical oxygen sensor. Measurements were taken at 5 locations in the anterior segment: 1) near corneal endothelium; 2) in the mid-anterior chamber (AC); 3) at the anterior surface of the lens or intraocular lens implant (IOL); 4) in the AC angle and 5) in the posterior chamber (PC; in cataract surgery patients only). pO2 close to the posterior surface of the lens and in the center of the vitreous were reported previously (Holekamp, et al. Am J Ophthalmol. 2005). Surgical history, systemic diseases and oxygen inhalation were recorded.
Oxygen measurements in the anterior segment were obtained from 92 eyes and in the vitreous, from 66 eyes. Baseline values were established from eyes with no previous surgery or diabetes. The mean pO2 values (mmHg) were: 22.1 ± 1.1 (cornea); 11.5 ± 0.7 (mid-AC); 3.1 ± 0.4 (anterior lens); 3.8 ± 0.6 (PC); 11.1 ± 0.6 (posterior lens) and 8.9 ± 0.6 (center of vitreous). Prior vitrectomy was associated with significantly increased oxygen levels in the PC (p=0.02), at the posterior surface of the lens (p=0.002) and center of the vitreous (p=0.003). Prior cataract surgery was associated with increased pO2 at the anterior surface of the IOL (p=0.002) and in the posterior chamber (p=0.038).
Three findings suggest that the human lens regulates oxygen levels and oxygen metabolites in the anterior segment: 1) A lower pO2 at the anterior than at the posterior of the lens. 2) After vitrectomy, higher pO2 in the posterior chamber, but not at the anterior surface of the lens. 3) Elevated pO2 in the PC and surface of the IOL in pseudophakic eyes. Our data are consistent with the hypothesis that the lens protects structures in the anterior segment from oxidative damage after vitrectomy. Removal of the vitreous gel causes elevation of oxygen in the posterior and anterior segment. Removal of the natural lens leads to increased oxygen in anterior segment of eye, which may alter the oxidative balance in these tissues, such as the trabecular meshwork. Studies are underway to investigate this possibility.
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