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L. Camras, M. Johnson; Osmotic Effects On Outflow Facility In Bovine Eyes . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1861.
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Recent studies have shown that in both bovine and human anterior segment perfusions, outflow facility (C) is decreased when the perfusion fluid is hypotonic and increased when it is hypertonic [IOVS 40: 1695–1701; IOVS 38(10):2165–71]. We examined this phenomena in whole bovine eyes.
Eyes were kept on ice and arrived at the laboratory within 4–12 hours of sacrifice. Each pair of bovine eyes was perfused with an isotonic solution (300 mOsm) as a control in one eye and an experimental solution (450 mOsm, 240 mOsm, or 150 mOsm) in the contralateral eye. The eyes were perfused at constant pressure of 10 mmHg for at least 150 mins. Both baseline facility (Co measured at 30–50 minutes after the start of perfusion) and wash–out rate were determined. Then, these data were analyzed statistically using a two–sided student t–test.
No consistent effect of osmotic pressure on outflow facility was seen. Hypotonic solutions showed an increase in facility as compared to controls contrary to the finding in perfused human anterior segments, but the effect was small and at best marginally statistically significant. Hypertonic solutions did show an increased outflow facility but this was not a statistically significant result. No effect was seen on wash–out rate.
Contrary to reported results in human and bovine anterior segment perfusions, changes in osmotic pressure had little if any significant effect on outflow facility in enucleated bovine eyes. This may be due to differences between enucleated eyes and perfused anterior segments, or there may have been acute changes in outflow facility (earlier than 30–50 minutes) that are not seen in longer perfusions. If the latter, this might imply that trabecular meshwork cells can quickly self–regulate their volume following an osmotic challenge.
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