The effects of anesthesia, mouse strain and age on intraocular pressure and an improved murine model of experimental glaucoma

Abstract

The purpose of this study was to improve a mouse model of chronic intraocular pressure (IOP) elevation utilizing microbead injection in two strains of mice and to assess the effect of age and anesthesia on measured IOP. We compared our previous model with two modified protocols for injecting polystyrene microbeads and viscoelastic material in CD1 or C57BL/6 mice. The measured outcomes were degree of IOP elevation and production of axonal loss. The first new protocol was injection of 3µL of equal volumes of 6µm and 1µm diameter beads, followed by 2µL of viscoelastic (3+2). The second new protocol injected 4µL of the two bead mixture, then 1µL of viscoelastic (4+1). Both were compared to injection of 2µL of 6µm beads with 3µL of viscoelastic (2+3). We also compared the effects of age and of two anesthetic regimens (intraperitoneal ketamine/xylazine/acepromazine versus isoflurane gas) on measured IOP in untreated eyes of both strains. IOP was 2 mm Hg lower with intraperitoneal than with gas anesthesia in both strains (p=0.003, p<0.0001, t-test). IOP measurements were lower in untreated young (2 months) compared to older (10 months) C57BL/6 mice (p=0.001, t-test). In the experimental glaucoma mouse model, mean IOP and number of elevated IOP measurements were higher in newer protocols. Mean axon loss with the 4+1 protocol (all strains) was twice that of the 2+3 and 3+2 protocols (36% vs. 15% loss, p = 0.0026, ANOVA), and mean axon loss in CD1 mice (21%) was greater than in C57BL/6 mice (13%) (p = 0.047, ANOVA). Median axon loss in 4+1 protocol treated C57BL/6 mice expressing yellow fluorescent protein in 2% of retinal ganglion cells (RGCs) had greater median axon loss than C57BL/6 4+1 protocol treated mice (26% vs. 10%, p=0.03). The 4+1 protocol provided higher, more consistent IOP elevation and greater axonal loss. The effects of age, strain, and anesthesia on induced IOP elevation and axon damage must be considered in mouse experimental glaucoma research.

Cyp1b1 Mediates Periostin Regulation of Trabecular Meshwork Development by Suppression of Oxidative Stress

“…Figure 1 shows a modest but statistically significant elevation of IOP in Cyp1b1 Ϫ/Ϫ mice compared with that in Cyp1b1 ϩ/ϩ mice. The mean IOP of Cyp1b1 ϩ/ϩ mice was 10.14 Ϯ 0.07 mm Hg, which is consistent with the previously reported value of 10.4 Ϯ 2.9 mm Hg (42). Correspondingly, the mean IOP of Cyp1b1 Ϫ/Ϫ mice was 11.45 Ϯ 0.20 mm Hg.…”

A Magnetic Microbead Occlusion Model to Induce Ocular Hypertension-Dependent Glaucoma in Mice

“…In these studies, the intracameral injection of polystyrene microbeads, alone or in combination with a viscoelastic material, resulted in IOP elevation leading to subsequent RGC death 6,10 . However, reflux when the needle is withdrawn from the eye and dislodging of microbeads from the iridocorneal angle are common problems that arise during the procedure.…”

“…The microbead occlusion model of glaucoma, first carried out in primates 12 , rabbits 8 , and rats 4,9,11 , was recently adapted for use in mice 5,6,10 . In these studies, the intracameral injection of polystyrene microbeads, alone or in combination with a viscoelastic material, resulted in IOP elevation leading to subsequent RGC death 6,10 .…”

“…In many of these models, glaucoma is induced by disrupting aqueous humour dynamics, resulting in the elevation of IOP. Occlusion models, in which microbeads or other substances are injected into the anterior chamber of the eye to block aqueous drainage, have gained popularity in recent years partly due to their relative ease to increase IOP [4][5][6][7][8][9][10][11][12][13][14] .…”

A Laser-induced Mouse Model of Chronic Ocular Hypertension to Characterize Visual Defects

“…Anesthesia significantly altered the IOP measurement and behavioral training of mice reduced IOP variation in awake animals 9,19 . Here, the experimental animals were given a few minutes to rest and adapt to the restrained position before measurement in order to get consistent readings of IOP.…”