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W. F. Abdallah, Jr., A. A. Fawzi, Jr., H. Ameri, Jr., G. Chader, Sr., M. Humayun, Jr.; Oxygenation of the Anterior Vitreous in a Rabbit Eye Model of Ischemia Reperfusion. Invest. Ophthalmol. Vis. Sci. 2009;50(13):153.
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To study the feasibility of oxygenation of the anterior vitreous using oxygen generating electrodes as a therapeutic modality for the treatment of acute retinal ischemia.
Baseline ERG and preretinal oxygen measurements were performed on normal pigmented rabbits. The intraocular pressure (IOP) of the right eye was elevated to 150mm Hg for 90 minutes through cannulation of the anterior chamber with a 25-gauge needle connected to a BSS bottle set at 140cm above the operating table. After 90 minutes, the cannula was removed, IOP was normalized, the preretinal O2 was measured and rabbits were divided into 2 groups: Oxygenation and Control. The Oxygenation group underwent vitreal oxygenation for 30 minutes using oxygen generating electrodes implanted into the anterior vitreous cavity through a pars plana sclerotomy. The control group underwent no oxygenation. Preretinal PO2 measurements were taken 30 minutes after the end of oxygenation i.e. one hour after reperfusion in both groups. Ten days after reperfusion, all rabbits underwent ERG recordings, were sacrificed and the eyes submitted for histopathology with 5x5mm slices of retinal samples subjected to superoxide dismutase (SOD) ELISA assay.
After 90 minutes of ischemia, preretinal PO2 recordings in all rabbits documented a significant reduction compared to the baseline readings (Mean: 21.6mmHg baseline; 2.5mmHg post-ischemia, p= 0.007). Following oxygenation in the oxygenation group, the preretinal O2 difference was statistically significant compared to post-ischemic PO2 values, (Mean: 13.7 mmHg 30 minutes after oxygenation, p=0.003). In the control group, the difference in preretinal PO2 one hour after reperfusion compared with the postischemic values was statistically insignificant (Mean: 5.7mmHg one hour after reperfusion , p=0.09).We compared the a-wave and b-wave amplitudes at baseline to final readings in both groups. The comparison showed a statistically significant decline of both a- and b- wave amplitudes in the control group (p-value= 0.028), while the oxygenated group showed no statistical significance (p-value= 0.678). SOD assays showed a statistically significant elevation in SOD in the control group (p-value= 0.001), and no statistical difference in the oxygenated eyes (p-value= 0.94) when compared with the contralateral normal eyes.
Short term oxygenation of the vitreous cavity in this rabbit ischemia reperfusion model was able to restore pre-retinal oxygen levels to near normal. ERG recordings, histological analysis and SOD assay pointed to preservation of the retinal structure and function in the oxygenated group compared to controls.
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