Deepening of the anterior chamber may impair the aqueous outflow system in guinea pigs

Abstract

Purpose : Myopia is a refractive condition that increases the risk of glaucoma. Studies have shown that the risk of developing glaucoma, especially primary open angle glaucoma (POAG), is more pronounced in high myopes. We hypothesized that excessive myopic eye growth may cause structural changes of the outflow system, leading to IOP elevation. Methods : Myopia was induced in healthy albino guinea pigs (n=24) by form deprivation (FD). A translucent plastic diffuser goggle was attached and randomly assigned to one of the guinea pig eyes. The ocular parameters including axial length (AXL), anterior chamber depth (ACD) and vitreous chamber depth (VCD); refractive error (Rx) and IOP were monitored regularly. After 3 to 8 weeks of FD, both eyes were removed and outflow facility was measured using constant flow method with perfusion system (iPerfusion). Results : The treated eyes became significantly more myopic (-4.63±0.67D, P<0.01), elongated (0.23±0.04mm, P<0.01) and with higher IOP (0.73±0.29mmHg, P=0.02) than fellow control eyes. In general, the IOP correlated well with the outflow facility (r=-0.40, P=0.05). Pearson correlation analysis revealed that myopic refraction was significantly correlated with axial elongation, but not with IOP and outflow facility. However, when the correlations in both eyes were studied together, intraocular change of ACD (δACD) was found to correlate moderately and significantly with δIOP (r=0.40, P<0.01) and outflow facility (r=-0.39, P=0.01). Conclusions : Axial elongation in albino guinea pigs correlated well with changes in the IOP and outflow facility. Specifically, eyes with deepened ACD showed significantly higher IOP and lower outflow facility. It indicated that ACD deepening may cause structurally changes that lead to gradual blockage of the aqueous outflow system and elevation of IOP.