[Comparison of two experimental models of glaucoma in rabbits]

Objective: to compare two models of experimental glaucoma by induction of ocular hypertension in rabbits.

Materials and methods: Sixteen New Zealand female rabbits, 2-3 kg were used. Model A (n=6): cauterization of episcleral and perilimbar veins of the right eye (RE) with surgical electrocautery. Model B (n=10): Injection of ?-chymotrypsin in posterior chamber of RE. Intraocular pressure (IOP) was measured before and after the induction of ocular hypertension (OHT), once a week at the same time of day for 40 days, with a manual tonometer. The animals were euthanized by CO2 inhalation. In both models the control was the IOP of the left eye (LE). The mean and standard error (SE) values of IOP, expressed in mmHg, were compared statistically by applying Student's t-test with a significance level of p<0.05.

Results: The IOP in LE (control) of model A: was 12.9±1.05 and in model B: 12.9±1.09. There were no significant differences between the models. Model A: The IOP increase in RE was 14.7% (14.8±1.4) with respect to LE. A significant increase in IOP was observed within the first 24 hours: 23.5±1.9 (p<0.05) compared to the control eye. There were no significant differences with subsequent controls. Model B: The increase in IOP in RE was 129.1% (29.6±3.4) with respect to LE. In all cases an increase was observed from Day 1 (p<0.05). The IOP peak in RE was evidenced on Day 25: 35±3.4 (p<0.05). The increase in IOP induced by model B was significantly higher (p<0.01) than in model A. There was loss of ganglion cells of the retina in both models, but the following anatomo-pathological changes were observed only in model B: buphthalmos, subluxation of the lens and increased excavation of the papilla.

Conclusion: This study indicates that model B is the most appropriate method to induce a rapid, controlled increase of IOP in rabbits and, more importantly, that this increase may be sustained over extended periods of time. This model could be useful for evaluating the efficacy of new ocular drug delivery systems and for further studies of the physiopathology of glaucoma.