Despite reducing elevated intraocular pressure (IOP) being the primary target for glaucoma treatment, nearly 40% of open-angle glaucoma patients don’t have elevated IOP. Recent studies show that glaucoma is not only a pressure-sensitive optic nerve disease; it’s also a neurodegenerative disease involving different types of light-sensitive retinal ganglion cells (RGCs). This aspect of glaucoma is not related to ocular pressure and paves the way for new research and treatment options.

What they did

According to Yvonne Ou, MD, associate professor in residence and academic director of the Glaucoma Division, Department of Ophthalmology, University of California San Francisco, retinal ganglion cells have “ON” cells that react to increases in light, and “OFF” cells that react to decreases in light. 

In one study, Ou artificially increased IOP in the eyes of mice for seven days and then allowed the IOP to return to baseline levels. During the process, Ou and her team evaluated:

• Loss and dysfunction of synapses (the gaps between nerve cells across which chemical messages are sent and received)
• Loss of density in dendrites (short branches of nerve cells allowing chemical messages to travel to the cell body)
• Radius of the receptive field (the region of visual space where changes in light intensity influence neuron activity)
• Electroretinography (ERG) amplitude (a frequency measurement of the retina’s response to light wave impulses in the ON and OFF ganglion cell pathways)

What they found

After the seven days of artificial IOP elevation and the return to baseline IOP, the research team found that, after IOP elevation:

• Synapse membrane density decreased.
• Dendrite density of RGCs remained stable.
• The radius of the receptive field increased.
• ON ganglion cells were more resilient than OFF ganglion cells after IOP elevation. 

What it means

While the ERG amplitude readings indicate that OFF ganglion cells may be more vulnerable in people with glaucoma, the resilience of ON ganglion cells suggest that their impaired function may be reversible. Since glaucoma has long been known as the leading cause of irreversible blindness, these new findings could bring hope to glaucoma patients everywhere.

*Charters, L., (2021, June 15). The 2 Faces of Glaucoma. Ophthalmology Times. https://www.ophthalmologytimes.com/view/the-2-faces-of-glaucoma