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J. Zhu, H. Gong; Morphological Changes Contributing to Decreased Outflow Facility Following Acute IOP Elevation in Normal Human Eyes. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1639.
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© ARVO (1962-2015); The Authors (2016-present)
Collapse of Schlemm’s canal (SC) and blockage of collector channel (CC) ostia by irreversible herniations of the inner wall of SC have been observed histologically as common features in primary open angle glaucoma (POAG) eyes even fixated at 0 mmHg (Gong et al, ARVO 07). This study is to determine whether these morphological changes exist in normal human eyes following an acute elevation of intraocular pressure (IOP) and whether they are reversible when IOP is decreased from high to normal levels.
Seven human eyes were studied within 24 hours postmortem. Three eyes in the experimental group were first perfused at 45 mmHg. After a stable baseline facility measurement, the perfusion pressure was decreased to 7 mmHg. Outflow facility was recorded continuously. The other four eyes were divided into two groups perfused at either 45mmHg or 7mmHg constantly as controls. Outflow facility was also recorded continuously. After perfusion fixation, anterior segments of the eyes were processed and the frontal sections (3µm) were cut in all of four quadrants. Using a light microscope, the herniations of SC inner wall were analyzed from at least eight CC ostia per eye; the changes in the SC’s width were also examined.
In the experimental group, the outflow facility at 45 mmHg (0.076±0. 014µl/ min/mmHg, mean±SE) was significantly lower than that at 7 mmHg (0.168±0.021µL/ min/mmHg, p=0.012). There was no significant difference in the outflow facility between the experimental and control groups either at 45mmHg (p=0.405) or at 7 mmHg (p=0.213). SC was the narrowest and most severely collapsed near CC ostia in the control 45 mmHg compared to both the experimental (45mmHg-7mmHg) group and the control 7 mmHg group. The percentage of CC ostia exhibiting herniations in the experimental group (22.36±2.80, mean±SE) was much lower compared to that in the control 45mmHg group (73.06±1.66, p=0.003), while it was still higher than that in the control 7mmHg group (12.88±0.73), but had no significant difference (p=0.17).
Decreasing outflow facility following acute IOP elevation coincides with the progressive collapse of SC and an increasing number of herniations into CC ostia. These changes appeared to be reversible when IOP was decreased from 45 mmHg to 7mmHg in normal human eyes. Our data suggest that collapse of SC and increasing numbers of herniations into CC ostia may contribute to the decreasing outflow facility following acute IOP elevation in human eyes. Additional factors rather than IOP increase may be involved in irreversible herniations found previously in POAG eyes.
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