ARVO 2024 presentation: Function-Structure Relationship in the Rat Glaucoma Model​​

Summary: Examining the link between retinal function and structure in ocular hypertension is crucial for glaucoma research. The rat magnetic microbead model, mimicking glaucoma aspects, provides insights into this relationship. The study aims to examine if behavioral, functional, and morphological parameters have correlation in the rat magnetic microbead glaucoma model.​

INTRODUCTION: Examining the link between retinal function and structure in ocular hypertension is crucial for glaucoma research. The rat magnetic microbead model, mimicking glaucoma aspects, provides insights into this relationship. The study aims to examine if behavioral, functional, and morphological parameters have correlation in the rat magnetic microbead glaucoma model.​

MATERIALS AND METHODS: Elevated intraocular pressure (IOP) was induced in 13-week-old male Brown Norway rats (N=18) using intracameral unilateral injection of magnetic microbeads. There were four study groups: No treatment (N=5), Saline (N=5), Bepoptic (N=5) and Näive (N=3). Rats received b.i.d. topical treatment of Saline and Bepoptic starting on the induction day and for the whole study period. IOP was monitored using the Tonolab rebound tonometer up to Day 28 post-induction. Weekly spectral-domain optical coherence tomography (SD-OCT) imaging was performed to quantify the inner retinal thickness. Pattern electroretinography (pERG) was recorded to assess retinal ganglion cell function. Visual acuity and sensitivity were also evaluated. Animals were sacrificed on Day 28 and retinal ganglion cells were immunostained with anti-RBPMS antibody and quantified using stereology.​

RESULTS: IOP was significantly elevated by Day 6 as compared to contralateral eyes (32.4 ± 3.0 vs. 10.8 ± 0.33 mmHg) and remained significantly elevated throughout follow-up Day 21. On Day 7, the inner retinal layer thickness was already slightly decreased in microbead-injected group as compared to naïve animals (0.053 ± 0.002 vs. 0.061 ± 0.001 μm, respectively). PERG (2.9 ± 0.7 vs. 7.6 ± 1.5 μV) and optomotor responses (0.375 ± 0.065 vs. 0.685 ± 0.025 cyc/°) were also significantly decreased in the microbead-injected group as compared to naïve. On Day 28, microbead-injected group had a significant decrease in pERG amplitude (2.8 ± 0.8 vs. 7.8 ± 1.4 μV) and visual acuity (0.361 ± 0.082 vs. 0.676 ± 0.018 cyc/°). Stereological analysis of retinal wholemounts revealed that the number of RBPMS-positive cells decreased by 48.8% in the microbead-injected eyes as compared to naïve eyes (1061 ± 246 vs. 2074 ± 82 cells/mm). From all correlational analyses, only visual acuity and inner retinal thickness correlated on Day 7 (r=0.84, P=0.001) and Day 14 (r=0.75, P=0.007). Other parameters did not correlate significantly between each other.​

Figure 1. Intraocular pressure (left image, mean± SEM) and total numbers of retinal ganglion cells labelled with RBPMS in different treatment groups (mean± SEM).

Figure 2. Inner retina layer thickness at different timepoints (left image). Data are presented as mean ± SEM. *** P <0.001. Visual acuity over the time course of the study (right image). Data are presented as mean ± SEM and were compared by Šídák’s multiple comparisons test, * P < 0.05, ** P < 0.005​.

CONCLUSIONS:
1. Visual acuity correlates with decreased inner retinal thickness on Day 7 and Day 14 post-injection in the rat magnetic microbead model.​
2. Bepoptic topical treatment did not exert functional and morphological protection of retinal ganglion cells.

Authors:  Kernius Mickevičius | Tomas Paulauskas | Robertas Čėsna | Marius Dragašius | Justina Urbanavičiūtė | Symantas Ragauskas | Giedrius Kalesnykas

Keywords: Glaucoma, IOP, RGCs, pERG, Optomotor testing