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J. Ho, H. Gong; Potential Role of a Short Scleral Spur in the Pathogenesis of Primary Open Angle Glaucoma. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3292.
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To determine if there is a significant difference in scleral spur length between primary open angle glaucoma (POAG) eyes and age-matched normal eyes. Secondly, to understand the potential role that scleral spur length may play in the pathogenesis of POAG.
Anterior segments of 11 POAG and 17 age-matched normal eye-bank eyes were fixed by immersion in Karnovsky’s fixative and processed for light and electron microscopic analysis. Three µm radial sections were cut and stained using 1% Toluidine blue. Light microscope images of the sections were then taken. Scleral spur length, ratio of the length of trabecular meshwork (TM) insertion into scleral spur to posterior length of the TM, and percent of Schlemm’s canal (SC) collapse were measured using Universal Desktop Ruler (Version 2.9.1124, AVPSoft). An electron microscopic examination of scleral spurs in POAG and normal eyes was conducted. Correlation of scleral spur length in POAG eyes versus their age at diagnosis of the disease was plotted. Finally, a mathematical analysis of an existing model was conducted to estimate the distances of POAG and normal scleral spur movement in vivo, and to determine if those distances would be sufficient to keep the SC open.
Average scleral spur length was significantly shorter in POAG (0.159 ± 0.036 mm, Mean ± SD) compared to normal eyes (0.206 ± 0.041 mm), p< 0.01. A higher percent of SC collapse was found in POAG (54.31 ± 38.67%) than in normal eyes (9.55 ± 23.63%), p< 0.01. The ratio of posterior TM insertion into scleral spur to posterior meshwork length was significantly greater in normal (0.765 ± 0.126), compared to POAG eyes (0.552 ± 0.160), p< 0.01. Fewer collagen bundles were seen in POAG scleral spurs compared to those in normal eyes by electron microscopy. A positive correlation (r= 0.832) was found between scleral spur length versus age at diagnosis of POAG. Mathematical analysis showed that scleral spur movement in POAG eyes was less than sufficient to maintain the stiffness of the TM to prevent the collapse of SC.
A shorter scleral spur is associated with a higher percent of SC collapse and an earlier age at diagnosis of POAG. Our data suggests that the shorter scleral spurs found in POAG eyes may be insufficient to hold the SC open, thus predisposing it to collapse, which may contribute to increased outflow resistance and intraocular pressure in POAG eyes.
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