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D.C. Beebe, N.M. Holekamp, Y.–B. Shui; Evidence That Increased Intraocular Oxygen Causes Nuclear Cataracts . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4638.
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Purpose: Previous studies showed that long–term, intermittent exposure to hyperbaric oxygen causes increased nuclear opacification and nuclear cataracts. The lens is normally in a hypoxic environment. Breakdown of the vitreous body is a major risk factor for nuclear cataracts. In those over 50, surgical vitrectomy is associated with a very high incidence (> 60%) of nuclear cataracts within two years. Avoiding vitrectomy during retinal surgery prevents nuclear cataract formation. The present study tested whether vitrectomy increases the exposure of the lens to oxygen. Methods: Procedures were approved by the Washington University Human Studies Committee. Patients who were undergoing retinal surgery for a variety of conditions and who provided informed consent were enrolled. O2 levels were measured just posterior to the lens equator and in the mid–vitreous cavity in sixty–nine eyes of sixty–six patients using a fiberoptic O2 optode (Oxford Optronics). Measurements were made at the beginning of the surgical procedure before the infusion was turned on and immediately after surgery. Results: Five eyes were excluded due to retained lens fragments after cataract surgery (2), rare retinal indications for retinal surgery (2) and because the infusion was turned on before making a measurement (1). For the included patients, O2 levels were higher posterior to the lens equator than in the mid–vitreous (11.1 ± 0.6 mm Hg vs. 8.9 ± 0.6 mm Hg, P < 0.0001). Similar values were found for a subset that excluded patients in which O2 levels might have been altered by preexisting ocular disease or exposure to O2 during surgery (8.7 ± 0.6 and 7.1 ± 0.5 mm Hg; P < 0.0001). O2 levels were much higher immediately after surgery (> 70 mm Hg; P < 0.0001 both locations). Compared to breathing < 60% O2, breathing > 90% O2 during surgery greatly increased O2 levels behind the lens and in the mid–vitreous (21.9 and 17.8, respectively; P < .0001). Eight patients who had a prior vitrectomy (mean time after initial vitrectomy 10 months, range 3 – 20 months) were matched on the basis of age, retinal diagnosis, phakic state, type of anesthesia and presence or absence of diabetes to patients receiving their first vitrectomy. For the control group, O2 levels were 10.3 ± 0.6 and 8.4 ± 0.7 mm Hg behind the lens and in the mid–vitreous, respectively. In patients with prior vitrectomy the values were significantly higher (12.9 ± 0.5 and 13.3 ± 0.8; P < 0.02 and 0.003, respectively). Conclusions: The increase in oxygen near the lens immediately after vitrectomy and for months after surgery is consistent with the hypothesis that increased exposure of the lens to oxygen causes nuclear cataracts.
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