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Abstract #9142 Published in IGR 5-2
Temporary elevation of the intraocular pressure by cauterization of vortex and episcleral veins in rats causes functional deficits in the retina and optic nerve
Grozdanic SD; Betts DM; Sakaguchi DS; Kwon YH; Kardon RH; Sonea IMExperimental Eye Research 2003; 77: 27-33
PURPOSE: To evaluate visual function in rats with chronic elevation of intraocular pressure (IOP). METHODS: Chronic ocular hypertension was induced in the left eye of 14 adult Brown Norway rats by cauterizing three vortex veins and two major episcleral veins; the right eye served as a non-operated control. A control group (n = 5) was sham operated on the left eye. Prior to surgery, the IOP was measured with a Tonopen, the pupil light reflex (PLR) evaluated with a custom-made computerized pupillometer and electroretinograms (ERGs) were recorded simultaneously from both eyes post surgically: IOP was measured on postoperative weeks 1, 3, 5 and 8, pupil light reflexes on postoperative weeks 1, 4 and 8, and ERGs on postoperative weeks 4 and 8. Sixty-five days postoperatively, rats were euthanized and optic nerves and eye globes were prepared for histological analysis. RESULTS: Seven days after surgery five of 14 rats developed significant elevation of the IOP in operated eyes (control eyes: 25.1 ± 0.5 mmHg; operated eyes: 34.1 ± 0.6 mmHg; mean ± SEM; p = 0.0004; paired t test). Elevation of the IOP was sustained at three (p = 0.002) and five (p = 0.007) weeks postoperatively. However, IOP values did not significantly differ between control and operated eyes eight weeks postoperatively (p = 0.192, paired t test). Sham operated animals showed no elevation of the IOP seven days postoperatively. When the ratio between consensual and direct PLR (PLR ratio = consensual/direct PLR; pupil of unoperated eye recorded) was examined in rats that developed IOP elevation, preoperative values were 92.2 ± 4% (mean ± SEM), one week postoperatively 65 ± 4% (significantly different from preoperative values, p > 0.05 repeated measures ANOVA with Dunnett's multiple comparison test, n = 5), four weeks postoperatively 60.6 ± 3.2% (p < 0•01, n=5). By eight weeks postoperatively, pupil responses had essentially recovered 75.4 ± 6.9% (p > 0.05, n = 5). Rats whose IOP values did not rise after surgery and sham operated rats did not develop pupil deficits four weeks postoperatively. Rats with elevated IOP displayed a significant decrease in ERG amplitudes in operated eyes at four weeks (a-waveoperated/a-wavecontrol (a-wave ratio) = 42 ± 14% (mean ± SEM); b-waveoperated/b-wavecontrol (b-wave ratio) = 43 ± 16%), but not at eight weeks postoperatively (a-wave RATIO = 88 ± 8.4%; b-wave RATIO = 82.9 ± 9%). Sham operated and rats whose IOP values remained non-elevated after surgery did not develop ERG deficits four weeks after surgery. Histological analysis did not reveal any damage in the eyes of animals with elevated IOP pressure with the exception of one rat, which still had ERG and pupil deficits at the end of the experiment. CONCLUSIONS: Development of ERG and PLR deficits are proportional to IOP elevation in the rat model of chronic ocular hypertension. Functional monitoring of the ERG and PLR are useful objective techniques for the detection of retina and optic nerve deficits.
Classification:
5 Experimental glaucoma; animal models
6.7 Electro-ophthalmodiagnosis (Part of: 6 Clinical examination methods)
