Temporary elevation of the intraocular pressure by cauterization of vortex and episcleral veins in rats causes functional deficits in the retina and optic nerve

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 3 vortex veins and 2 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 weeks 1, 3, 5 and 8 post-operatively, pupil light reflexes on weeks 1, 4 and 8 post-operatively, and ERGs on weeks 4 and 8 post-operatively. Sixty five days postoperatively, rats were euthanized and optic nerves and eye globes were prepared for histological analysis. Results. Seven days after surgery 5/14 rats developed significant elevation of the IOP in operated eyes (control eyes: 25·1±0·5mmHg; operated eyes: 34·1±0·6mmHg; mean±SEM; p=0·0004; Paired t-test). Elevation of the IOP was sustained at 3 ( p=0·002) and 5 ( p=0·007) weeks postoperatively. However, IOP values did not significantly differ between control and operated eyes 8 weeks postoperatively ( p=0·192, Paired t-test). Sham operated animals showed no elevation of the IOP 7 days postoperatively. When the ratio between consensual and direct PLR (PLR ratio=consensual/direct PLR; pupil of unoperated eye recorded) was examined in rats which developed elevation of the IOP, preoperative values were 92·2±4% (mean±SEM), 1 week postoperatively 65±4% (significantly different from preoperative values, p