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Y. Zhang, Z. Lu, T. Freddo, H. Gong; Hydrodynamic and Morphological Changes During Washout in Monkey Eyes. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1613.
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To better understand the physiology of the washout effect in monkey eyes in order to exploit it as a means of reducing IOP in human eyes with glaucoma.
Eight enucleated monkey eyes were used in this study. Within 24 hours postmortem, eyes were perfused with Dulbecco's PBS containing 5.5mM glucose at 15mmHg for long-duration (180 minutes) or short-duration (30 minutes, n= 4 for each group). The eyes were perfused with red fluorescent microspheres (0.5µm; 0.002% v/v) to trace the hydrodynamic patterns of outflow, and then were perfusion-fixed with Karnovsky’s fixative at the same pressure. Radial and frontal sections in all quadrants were prepared and confocal images were taken along the inner wall (IW) of the Schlemm’s canal (SC). The total length (TL) and the tracer-decorated length (L) of IW were measured in >16 images/eye, and the average percent effective filtration length (PEFL=L/TL) was calculated for each eye. The sections with SC were processed and examined under light and electron microscopy. The TL of IW and the length exhibiting separation (SL) in juxtacanalicular connective tissue (JCT) were measured. The average percent separation length (PLS= SL/TL) was calculated.
Outflow facility increased 150% [1.46±0.70µl/min/mmHg (mean±SE), p<0.01] from baseline facility (0.58±0.20µl/min/mmHg) after 180 minutes perfusion to induce washout. No significant increases were found in outflow facility after 30 minutes perfusion (0.44±0.16µl/min/mmHg) compared to baseline (0.62±0.21µl/min/mmHg, p=0.46). A more uniform tracer pattern was seen in long-duration perfusion eyes than in short-duration perfusion eyes. The average PEFL in long-duration eyes (83.37±4.13%) was 3.4-fold larger than in short-duration eyes (24.19±8.42%, P<0.001). The JCT region appeared distended in long-duration eyes compared with short-duration eyes. The connections between JCT cells and between JCT cell and matrix were lost in expansion regions. The PLS in JCT region was 2.3-fold larger in long-duration eyes (77.4±3.2%) than that in short-duration eyes (33.5±5.3%, p<0.001).
Increasing outflow facility during washout coincides with an increase in available area for aqueous humor outflow. These hydrodynamic changes are likely driven by morphologic changes associated with a decrease in cell-cell and cell-matrix connections in the JCT region.
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