Chronic Ocular Hypertension Induced by Circumlimbal Suture in Rats

PURPOSE. To induce chronic intraocular pressure (IOP) elevation in rat eyes by circumlimbal suture. METHODS. Anesthetized (isoflurane) Long-Evans rats underwent unilateral circumlimbal suture implantation while the fellow eyes served as untreated controls (n = 15). A sham group (n = 8) received the same procedure except that the suture was loosely tied. Intraocular pressure, electroretinography (ERG), and optical coherence tomography (OCT) were monitored for 15 weeks, after which retinal histology and immunofluorescence staining for glial fibrillary acidic protein (GFAP) and ionized calcium binding adapter molecule-1 (Iba-1) were undertaken. RESULTS. Both IOP and ERG remained unaltered in the sham and all control eyes over 15 weeks. In the ocular hypertensive eye, IOP spiked from 17 +/- 1 to 58 +/- 3 mm Hg immediately after suture application, recovering to 32 +/- 2 mm Hg by 24 hours, and remained elevated by 7 to 10 mm Hg above baseline for 15 weeks. At week 2, there was a small reduction of ERG components involving the photoreceptor a-wave, bipolar cell b-wave, and ganglion cell-mediated scotopic threshold response (pSTR). The reduction in a- and b-wave remained stable, while the pSTR became more affected from week 8 onward (P < 0.05). By week 12, there was progressive retinal nerve fiber layer (RNFL) thinning. At week 15, GFAP expression was upregulated in inner retina and on Muller cells. The ganglion cell dysfunction was associated with RNFL thinning and cell loss in the ganglion cell layer. CONCLUSIONS. Circumlimbal suture provides a simple and cost-effective way to induce mild chronic ocular hypertension in rat eyes. This model produces preferential ganglion cell dysfunction and RNFL reduction.