Ocular Hypertension Model Induced by Episcleral Vein Cauterization for Screening Retinal Ganglion Cells Neuroprotection Therapies in Brown Norway Rats

Abstract

Purpose : The purpose of the study was to demonstrate an ocular hypertension (OHT) model by episcleral vein cauterization in Brown Norway rats as a way of screening new therapies for retinal ganglion cells (RGC) neuroprotection, by evaluating intraocular pressure (IOP) elevation and RGC loss over 12 weeks.

Methods : Cauterization of three episcleral veins was performed in one eye per animal in male Brown Norway rats (n=24). The cauterized eye was designated as the OHT eye and the untreated eye as the non-OHT eye. IOP measurements were obtained in both eyes pre-cauterization (week 0), weekly and pre-sacrifice and, 8 animals were sacrificed at the end of 4, 8 and 12 weeks. Both eyes were enucleated and fixed overnight in 4% paraformaldehyde fixative at 4 ± 2°C. Retinas were dissected out and processed for immunohistochemistry using anti-Brn-3a (primary antibody) and Alexa Fluor 594 (secondary antibody). RGCs staining was imaged using fluorescence microscopy and quantified using Image J. IOP elevation in the OHT eye was calculated as the IOP difference between the non-OHT eye and the OHT eye per animal and averaged across all animals (Mean ΔIOP) at each time-point. Percent RGC loss in the OHT retinas was calculated considering the RGC counts in each non-OHT eye to be 100%.

Results : The mean ΔIOP at Week 4 (n=24), 8 (n=16) and 12 (n=8) was 8.83, 16.78 and 15.59 (mmHg) respectively. One-way ANOVA comparing the IOP measurements taken at all the time-points revealed a statistically significant increase (p=.00) in IOPs taken at Week 5 and time-points after (Weeks 6-12) compared to week 4 and time-points before (Weeks 0-3). The overall percent RGC loss at 12 weeks in the OHT retinas was 35.5 ± 5.22 (mean ± SD) %. Paired t-test comparing the mean RGC count showed a statistically significant decrease 1018.4 ± 145.9 (mean ± SD) cells/mm² (p=.00) in the OHT eyes compared to the non-OHT eyes at 12 weeks.

Conclusions : Episcleral vein cauterization can be validated as a successful model for inducing Ocular Hypertension (OHT) in Brown Norway Rats. The model can be used for potentially screening or testing therapies for RGC neuroprotection after 4 weeks, when the increase in intraocular pressure stabilizes and is maintained at least until 12 weeks.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.