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D.C. Beebe, N.M. Holekamp, Y.–B. Shui, B. Kramer, S. Mangers; Oxygen Consumption by Human Vitreous Humor: Implications for the Formation of Postvitrectomy Nuclear Cataracts . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4739.
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© ARVO (1962-2015); The Authors (2016-present)
Previous studies showed that loss of the gel structure of the vitreous body, either during aging or after vitrectomy, is associated with the formation of nuclear cataracts. Exposure to excess oxygen is also linked to nuclear cataract formation. The present study tested whether the metabolic activity of the vitreous humor contributes to the low oxygen levels found in the eye.
Prospectively, 0.3 ml of undiluted vitreous was removed from consenting patients undergoing vitrectomy surgery. The sample was immediately transferred to a custom–designed respirometer and oxygen consumption was measured at 35°C. using an Oxylab pO2 optical oxygen sensor (optode; Oxford Optronix, Oxford, UK). Optodes were calibrated before use and accuracy was confirmed after each measurement.
Previous results from our laboratory showed that vitreous humor obtained from eye bank eyes rapidly consumes oxygen in an ascorbate–dependent manner (N = 12; Mangers, et al., ARVO abstract submitted). Oxygen consumption did not involve cellular respiration. To test whether oxygen consumption in vitreous humor from eye bank eyes might be a postmortem artifact, a small sample of undiluted vitreous humor was obtained at the time of initial vitrectomy surgery from patients undergoing surgery for macular hole or preretinal membranes. In these samples oxygen was consumed at an initial rate of 0.86 ± 0.03 µl·hr–1·ml–1 (N = 4). We reported that prior vitrectomy was associated with an increase in the levels of oxygen around the lens (Holekamp, et al. Am J Ophthalmol 2005). Therefore, oxygen consumption was measured in the vitreous fluid of patients who had a prior vitrectomy but required a second surgery to repair a macular hole or retinal detachment. In this group, mean oxygen consumption by the fluid in the vitreous chamber was 0.31 ± 0.13 µl·hr–1·ml–1 (N = 3). The difference between the oxygen consumption by gel vitreous and the liquid present after vitreous surgery was statistically significant (p = 0.05; t–test assuming unequal variance). We are testing whether this relationship holds for a larger group of specimens.
Human vitreous humor obtained at the time of vitrectomy consumes oxygen. Oxygen consumption appears to be lower in patients who have had a prior vitrectomy. Lowered oxygen consumption in the vitreous fluid could explain the increased oxygen levels in eyes with a prior vitrectomy and the high incidence of nuclear cataracts following vitrectomy.
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