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Y. Zhang, C. B. Toris, H. Gong; Morphological and Hydrodynamic Correlates in Monkey Eyes With Laser-Induced Glaucoma. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2080.
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To investigate the morphological and hydrodynamic changes of laser-induced glaucoma in cynomolgus monkey eyes.
Argon laser photocoagulation burns to the trabecular meshwork (TM) were made in one eye of each monkey (N=3), leaving the control eyes as a normotensive control. Laser treatments were repeated monthly for up to three times to establish a stable increase in intraocular pressure (IOP). At 1.3-5.8 (Mean±SE=3.7±2.3) years later, measurements were made of IOP by pneumatonometry and outflow facility (C) by fluorophotometry. Within 24 hours postmortem, eyes were perfused with Dulbecco's PBS containing 5.5mM glucose and red fluorescent microspheres (0.5µm; 0.002% ) for 30 minutes (at the last pressure measured before death minus 7mmHg) to label the hydrodymamic patterns of outflow. The eyes were perfusion-fixed with Karnovsky’s fixative at the same pressure. Radial and tangential sections to the limbus and perpendicular to the ocular surface in all quadrants were cut 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 >15 images/eye, and the average percent effective filtration length (PEFL=L/TL) was calculated for each eye. The sections with SC were then processed and examined under light and electron microscopy.
The average IOP of laser treated eyes was 62.0±3.5 mmHg, which was significantly higher than controls (22.7±4.0 mmHg, P<0.001), while the average C (0.03±0.02 µl/min/mmHg) was 13-fold lower in laser-treated eyes than controls (0.39±0.17 µl/min/mmHg, P<0.001). Laser treated eyes showed segmental distribution of tracer in the TM, while controls showed a more uniform outflow pattern, with extensive labeling along the SC. The average PEFL in controls (45.06±7.60%) was 2.9-fold larger than in laser treated eyes (15.40±7.80%, P<0.001). There was extensive pigmentation throughout the TM of laser treated eyes and most of the SC collapsed, with focal herniations of the IW and the juxtacanalicular connective tissue protruding partly into the collector channel ostia. In addition, there was an increase in the size and number of vacuoles in the herniated region. Trabecular cell division was found localized to the anterior, nonfiltering region of the TM, where it inserts into the cornea beneath Schwalbe’s line.
Reduction in the area available for outflow across the IW of SC, collapse of SC and the presence of herniations in the collector channel ostia may partly explain the IOP associated decrease in outflow facility in laser-induced glaucoma.
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