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

Abstract

The use of rodent models of glaucoma has been essential to understand the molecular mechanisms that underlie the pathophysiology of this multifactorial neurodegenerative disease. With the advent of numerous transgenic mouse lines, there is increasing interest in inducible murine models of ocular hypertension. Here, we present an occlusion model of glaucoma based on the injection of magnetic microbeads into the anterior chamber of the eye using a modified microneedle with a facetted bevel. The magnetic microbeads are attracted to the iridocorneal angle using a handheld magnet to block the drainage of aqueous humour from the anterior chamber. This disruption in aqueous dynamics results in a steady elevation of intraocular pressure, which subsequently leads to the loss of retinal ganglion cells, as observed in human glaucoma patients. The microbead occlusion model presented in this manuscript is simple compared to other inducible models of glaucoma and also highly effective and reproducible. Importantly, the modifications presented here minimize common issues that often arise in occlusion models. First, the use of a bevelled glass microneedle prevents backflow of microbeads and ensures that minimal damage occurs to the cornea during the injection, thus reducing injury-related effects. Second, the use of magnetic microbeads ensures the ability to attract most beads to the iridocorneal angle, effectively reducing the number of beads floating in the anterior chamber avoiding contact with other structures (e.g., iris, lens). Lastly, the use of a handheld magnet allows flexibility when handling the small mouse eye to efficiently direct the magnetic microbeads and ensure that there is little reflux of the microbeads from the eye when the microneedle is withdrawn. In summary, the microbead occlusion mouse model presented here is a powerful investigative tool to study neurodegenerative changes that occur during the onset and progression of glaucoma.

Optogenetic Stimulation of the Superior Colliculus Confers Retinal Neuroprotection in a Mouse Glaucoma Model

“…Valiente-Soriano et al (2015) describe a near-perfect linear correlation between survival of Brn3a ϩ cells and preservation of retrograde axonal transport in the LP model applied here. Furthermore, comparisons between axon counts in the optic nerve and Brn3a ϩ cell numbers are lacking for the LP model, but these measurements are in excellent correspondence in the microbead model, in which elevated IOP is achieved by intracameral injection of beads (Cone et al, 2010;Chen et al, 2011;Ito et al, 2016). Together, these results demonstrate that preservation of somatic Brn3a immunoreactivity is linked with other aspects of RGC integrity.…”

A murine glaucoma model induced by rapid in vivo photopolymerization of hyaluronic acid glycidyl methacrylate

“…Furthermore, the aggregation of microbeads in the inferior (ventral) region often caused focal hemorrhage and corneal synechiae to >50% of the injected eyes (unpublished in-house observation) potentially confounding the mechanisms in neurodegeneration. Modified approaches have been reported by different groups, such as mixing the microbeads with viscoelastic solution [ 31 ] or using magnetic microbeads and a handheld magnet [ 33 ] to prevent microbeads reflux after injection and improve the bead distribution in the anterior chamber, however, the effects were only short term and subsequent re-injection was needed for a subset of animals. A circumlimbal suture approach has recently been reported by Zhao and colleagues (2017) where circumlimbal suture was applied at 5–6 subconjunctival anchor points behind the limbus to induce chronic IOP elevation in mice [ 28 ].…”

Review of rodent hypertensive glaucoma models

“…Ito et al. () reported a gradual loss of RGC during the first 3 weeks after a single magnetic microbeads injection; the RGC loss remained stable at around 22–25% between 3 and 6 weeks possibly due to C57BL/6 mice being resistant to RGC damage. A modification to the original technique involves using a toroidal‐shaped magnet to rapidly draw the beads to the iridocorneal angle (Bunker et al.…”