Evaluation of retinal ganglion cell loss in a hydrogel-mediated mouse model of glaucoma after 6 months of IOP elevation

Abstract

Purpose : Chronic, progressive degeneration of retinal ganglion cells (RGCs) is a hallmark of glaucoma. While thinning of the retinal nerve fiber layer (RNFL) and ganglion cell inner plexiform layer (GCIPL) can be monitored using OCT, the distribution and rate of loss of RGC soma in glaucomatous eyes remains elusive. In this study, we evaluated the pattern and degree of RGC loss in a hydrogel-mediated mouse model of glaucoma after 6 months of intraocular pressure (IOP) elevation.

Methods : Intracameral injection of a hydrogel was performed in one eye of 18-month-old mice for elevation of IOP for six months. Contralateral eyes were control. Measurement of IOP was performed using a tonometer for every 2-3 days. Retinas were then immunostained with RBPMS (RGC marker), imaged using Nikon AR, and analyzed between sup, nas, inf, and tem quadrants with central, middle, and peripheral regions as <800mm, 800-1600mm, and >1600mm from the optic nerve head, respectively. RGCs were counted using binary function of NIS-Elements AR with manual correction. Kruskal-Wallis and Wilcoxon rank sum tests were performed using Stata16.0. P-value <0.05 was considered significant. Data are in mean±sem.

Results : Average increase in IOP AUC of gel-injected eyes was 47.9±4.2% higher than contralateral control eyes (Figure 1). RGC loss was detected in all gel-injected eyes compared with the control eyes (p<0.001). There was an average 20±2% RGC loss in eyes injected with hydrogel (2370.4±324.4 RGCs/mm²), compared to contralateral control eyes (3366.8±111.5 RGCs/mm²) (Figure 2). Superior quadrants were found to have the greatest RGC loss (p<=0.003), with peripheral regions showing greatest RGC loss regardless of retinal quadrant (p<0.001).

Conclusions : This study demonstrates that our hydrogel-mediated mouse model of glaucoma is able to sustain long-term IOP elevation for up to 6 months after a single intracameral injection. RGC loss was greatest in the superior quadrant, and predominantly located in peripheral regions. Further study is needed to elucidate the relationship between RGC loss and axonal fiber loss of the optic nerve.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.

 

Figure 1. Summary of intraocular pressure profile of gel-injected and contralateral control eyes (n=6 mice) over six months. Data are in mean±sem.

 

Figure 2. Representative fluorescent images of RBPMS staining in a control (A) and gel-injected (B) eye of the same mouse. Scale bar 500µm.