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Hana Levkovitch-Verbin, Harry A. Quigley, Keith R. G. Martin, Danielle Valenta, Lisa A. Baumrind, Mary Ellen Pease; Translimbal Laser Photocoagulation to the Trabecular Meshwork as a Model of Glaucoma in Rats. Invest. Ophthalmol. Vis. Sci. 2002;43(2):402-410.
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purpose. To develop and characterize a model of pressure-induced optic
neuropathy in rats.
methods. Experimental glaucoma was induced unilaterally in 174 Wistar rats,
using a diode laser with wavelength of 532 nm aimed at the trabecular
meshwork and episcleral veins (combination treatment group) or only at
the trabecular meshwork (trabecular group) through the external limbus.
Intraocular pressure (IOP) was measured by a tonometer in rats under
ketamine-xylazine anesthesia. Possible retinal vascular compromise was
evaluated by repeated fundus examinations and by histology. The degree
of retinal ganglion cell (RGC) loss was assessed by a masked,
semiautomated counting of optic nerve axons. Effects of laser treatment
on anterior ocular structures and retina were judged by light
results. After the laser treatment, IOP was increased in all eyes to higher than
the normal mean IOP of 19.4 ± 2.1 mm Hg (270 eyes). Peak IOP was
49.0 ± 6.1 mm Hg (n = 108) in the combination
group that was treated by a laser setting of 0.7 seconds and 0.4 W and
34.0 ± 5.7 mm Hg (n = 46) in the trabecular group.
Mean IOP after 6 weeks was 25.5 ± 2.9 mm Hg in glaucomatous eyes
in the combination group compared with 22.0 ± 1.8 mm Hg in the
trabecular group. IOP in the glaucomatous eyes was typically higher
than in the control eyes for at least 3 weeks. In the combination
group, RGC loss was 16.1% ± 14.4% at 1 week (n = 8, P = 0.01), 59.7% ± 25.7% at 6 weeks (n= 88, P < 0.001), and 70.9% ± 23.6% at
9 weeks (n = 12, P < 0.001). The
trabecular group had mean axonal loss of 19.1% ± 14.0% at 3 weeks
(n = 9, P = 0.004) and 24.3% ± 20.2%
at 6 weeks (n = 25, P < 0.001),
increasing to 48.4% ± 32.8% at 9 weeks (n = 12, P < 0.001). Laser treatment led to closure of
intertrabecular spaces and the major outflow channel. The retina and
choroid were normal by ophthalmoscopy at all times after treatment.
Light microscopic examination showed only loss of RGCs and their nerve
conclusions. Increased IOP caused by a laser injury to the trabecular meshwork
represents a useful and efficient model of experimental glaucoma in
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