Modified model of elevated intraocular pressure causes progressive retinal ganglion cell degeneration in mice

Abstract

Purpose : An essential pathogenesis of glaucoma is a loss of retinal ganglion cells (RGCs) accompanied with glaucomatous optic disc cupping. Persistent high intraocular pressure (IOP) is one of the major risk factors for the progression of glaucoma. The purpose of this study is to develop an improved mouse model of ocular hypertension, which induces long-lasting IOP elevation and robust damage to RGCs.

Methods : Mice were anesthetized and 6.0 μl of beads mixed with hyaluronic acid was injected into the anterior chamber (mixture group). IOP was measured every 3 days with the TonoLab tonometer. Four weeks after beads injection, RGC damage was assessed in the peripheral and midperipheral retina using whole retina immunostaining with Brn-3a, a specific marker of RGCs. We compared the change of IOP and damage to RGCs in the mixture group with a well-known microbead occlusion glaucoma model, 3.0 μl injection of beads in saline solution, (original group) and eyes injected with 6.0 μl of hyaluronic acid (hyaluronic acid group), used as control eyes. All data were shown as mean ± SD.

Results : The elevation of IOP in the mixture group showed a bimodal peak during the 4-week follow up period. The first peak occurred 1-hour post beads injection, with a value of 44.69 ± 6.00 mmHg, and the second peak occurred 6-12 days post injection, with a value of 34.91 ± 5.21 mmHg. IOP in the mixture group was significantly higher than that in the original and hyaluronic acid group during the 4-week follow up period (p < 0.0001). Maximum damage to RGCs was identified in the periphery of the mixture group, with a loss of 64.1%, which is a significant decrease compared to normal eyes (p < 0.0001). A significant reduction of midperipheral RGCs was also identified, with a loss of 32.4% (p < 0.0001).

Conclusions : Injection of beads mixed with hyaluronic acid induced sustained IOP elevation and severe damage to RGCs, which was easily reproducible. Sustained elevation of IOP leads to increased damage to RGCs in the periphery, compared to those in the midperiphery. This method is useful in understanding the pathology of RGC death, which results due to elevated IOP, as it contains a marked increase in RGC cell death over the original bead occlusion model.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.