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Karthik Murali, Ramiro Ribeiro, James Weiland, Mark Humayun; Spatio-Temporal Characteristics Of Oxygen Diffusion In The Vitreous Humor. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5331.
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To investigate the spatio-temporal characteristics of oxygen diffusion in the vitreous humor of the eye with the aim of creating an in-vitro model for ocular oxygen diffusion.
A point source of oxygen was created in 3 different media: saline, enucleated pig eyes’ vitreous, and live rabbits’ vitreous. 2 platinum/Iridium (80/20) electrodes with exposed surface area of 0.3mm2 each were used to perform electrolysis under a monophasic current pulse train. The pulse amplitude was 1.5mA, pulse duration was 200 μs, and the pulse period was 10 ms. Under these conditions, 0.078 nmol of O2/min was generated. An oxygen probe was placed 0.5mm away from the oxygen producing electrode (anode) and oxygen tension was recorded over time in the aforementioned media. In the enucleated pig eyes and in the rabbit eyes, the electrodes were placed close to the optic disk.
The data collected suggests that oxygen diffusion in saline is faster than oxygen diffusion in the other two media. The oxygen tension in saline increased from 30mmHg to more than 200 mmHg in less than a minute when the oxygen source is 0.5mm away from the oxygen measuring probe. Since the oxygen probe cannot measure partial pressures above 200mmHg, there are no data points after 1 minute. In both in-vitro and in-vivo vitreous humor, the oxygen tension rises from 5mmHg to about 55mmHg over 30 minutes, when the oxygen source is 0.5mm away from the oxygen measuring probe.
The data collected suggests that in vitro tests of oxygen diffusion cannot be modeled on saline since the diffusion dynamics of oxygen in saline is very different from that of vitreous humor. Enucleated pig eyes seem to be a good model for in-vivo experiments.
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