Latex bead injection model useful for studying retinal ganglion cell loss

A new model for latex bead injections demonstrates that this is a viable approach to increasing IOP and inducing loss of retinal ganglion cells in rats, said Rebecca M. Sappington, PhD, research fellow, Vanderbilt University, Vanderbilt Eye Institute, Nashville.

Using a model adapted from earlier designs, Dr. Sappington and colleagues injected fluorescent latex beads 15 mm in diameter into the anterior chamber of one eye and saline into the other eye in a group of adult Norway Brown rats.

Investigators used a tonometer (Tono-Pen, Reichert Inc.) to measure IOP in awake rats and used the mean of 25 measurements to calculate changes over time. They also measured axonal area and loss of axons and performed histologic examinations. They were able to elevate IOP for up to at least 5 weeks by giving the rats two injections of beads; IOP levels increased by 30% to 40% over this period. A single injection reduced IOP about 30% over 2 weeks.

Investigators also observed that a 2.5-ml injection produced a slow rise in IOP, while a 5-ml injection produced a large initial increase. In addition, after 2 weeks of elevated IOP, eyes injected with the higher dose of latex beads showed a greater reduction in distal nerve retinal ganglion cells than in proximal nerve cells. In contrast, eyes that had been given the 5-ml injection of beads showed the same pattern of axon loss in the proximal and distal nerves, Dr. Sappington said. At 5 weeks, more severe axonal loss was again found in the distal nerve than in the proximal nerve in eyes that had received the smaller injection of beads. In eyes receiving the larger injection, the loss pattern remained consistent between the two types of nerves.