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D. C. Beebe, Y.-B. Shui, N. M. Holekamp, B. C. Kramer; The Importance of the Vitreous Gel in Protecting Against Nuclear Cataracts. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4918.
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© ARVO (1962-2015); The Authors (2016-present)
Loss of the gel structure of the vitreous body and exposure of the lens to excess oxygen have been linked to nuclear cataract formation in humans. We previously reported that vitreous humor obtained from eye bank eyes rapidly consumes oxygen in an ascorbate-dependent manner (Mangers, et al., ARVO 2006) and suggested that vitrectomy might be associated with lower rate of oxygen consumption by the vitreous (Beebe, et al. ARVO 2006). The present study determined whether there is a relationship between the gel state of the vitreous, ascorbate levels in the vitreous and oxygen consumption by the vitreous humor in patients undergoing retinal surgery.
Undiluted vitreous was removed from consenting patients before vitrectomy or from patients who had undergone a previous vitrectomy. An aliquot 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). Ascorbate levels were determined using a colorimetric method. Gel state of the vitreous was scored on a subjective scale in isolated vitreous and during vitrectomy surgery.
Vitreous humor was obtained from consenting patients undergoing an initial or follow up retinal surgery for macular hole, diabetic retinopathy or preretinal membranes. Prior vitrectomy was associated with a greater than 50% reduction in the rate of oxygen consumption by vitreous humor (p < 0.01). At the time of first retinal surgery, patients with more gel vitreous consumed oxygen at an initial rate of 0.024 µl·hr-1·ml-1 (n = 26), which was significantly faster than those with more liquid vitreous (0.014 µl·hr-1·ml-1; n = 19; p < 0.01). The rate of oxygen consumption was related to ascorbate concentration. Ascorbate levels in patients with more gel vitreous, more liquid vitreous, or with a prior vitrectomy were 1.89 mM (n = 14), 0.97 mM (n = 11) and 0.79 mM (n = 7), respectively. Ascorbate levels in patients with more gel vitreous were significantly greater than in those with more liquid vitreous (p < 0.05) or after vitrectomy (p < 0.01).
Loss of the gel structure of the vitreous body, either due to age-related degeneration or vitrectomy, is associated with decreased oxygen consumption and lower levels of ascorbate. In the absence of the vitreous gel, increased mixing of the vitreous with oxygen from the retina may accelerate the degradation of ascorbate and expose the lens to higher concentrations of oxygen, leading to nuclear cataract formation.
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