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Editors Selection IGR 17-4

Basic Research: Modified rodent model of elevated IOP

Comment by John Morrison on:

45711 A novel method for the induction of experimental glaucoma using magnetic microspheres, Samsel PA; Kisiswa L; Erichsen JT et al., Investigative Ophthalmology and Visual Science, 2011; 52: 1671-1675

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Rodent models of elevated IOP provide insights into mechanisms of optic nerve damage pertinent to glaucoma. Samsel et al. (610) describe a modification of the anterior chamber microbead injection model. By using paramagnetic polystyrene microspheres, the authors hope to move the beads into the anterior chamber angle with a magnet to improve delivery to the trabecular meshwork. Sixty-one Brown Norway rats received up to three unilateral anterior chamber injections of a 30 mg/mL solution of 5 μm ferro-magnetic microspheres, and the beads were drawn to the peripheral anterior chamber using a 0.45 Tesla magnet. Awake IOPs were determined using topical anesthesia and repeat injections performed when experimental eye IOP fell to within 5 mmHg of the fellow eye. Sixty-four percent of eyes demonstrated a 5 mmHg IOP rise for a minimum of seven days, and 36% showed IOP fluctuation. Mean duration of elevation following one injection was nearly 13 days. Light microscopy confirmed bead deposition in the trabecular meshwork. Retinal ganglion cell loss in a subgroup of eyes was 36.4%.

Several individual pressures exceeded 50 mmHg, and occasionally approached 60. However, these readings, obtained in animals housed in constant light to minimize circadian fluctuation and without general anesthetics that can lower IOP, represent a true reflection of the maximum extent of pressure elevation. Animals receiving microbeads without magnet application demonstrated no significant IOP increases, strongly suggesting that magnetic redistribution helps achieve a reasonable rate of pressure elevation with a relatively low number of injections. Unfortunately, clear comparisons with prior reports using non-magnetic microbeads are difficult, due to differences in microsphere sizes. Nevertheless, this is a useful modification of the microbead model that can also be applied to mice. Importantly, the magnet also clears the visual axis, allowing application of in vivo studies, such as posterior segment imaging and electroretinography to the microbead model.

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