Magnesium may guard vision, but timing and concentration narrow the therapeutic window

Retinal ganglion cells, or RGCs, are the final connection between the eye and the brain. They collect visual information, and if these cells die, the lost connection cannot easily be repaired. This can happen in conditions like glaucoma, which affects over 70 million people worldwide, or after optic nerve injuries. One factor that damages RGCs is excessive glutamate, a chemical that carries signals between neurons.

When there is too much glutamate, it overactivates NMDA receptors, allowing calcium ions to enter the cell. Calcium is necessary for the cell, but too much of it can damage proteins, membranes, and DNA. Magnesium acts as a natural damper, partially blocking the NMDA receptor channel and limiting calcium influx. The study found that magnesium can protect RGCs by curbing dangerous calcium overload without completely cutting off information transmission.

The key was finding the right balance between protection and preserving function. The researchers built a model of a single retinal ganglion cell, incorporating sodium, potassium, and calcium channels, as well as AMPA and NMDA receptors. They tested different magnesium concentrations (0.2 to 2.5 mM) and frequencies (10, 30, 60, 80, 90, and 100 Hz).

At physiological frequencies (10-60 Hz), increasing magnesium concentration reduced calcium accumulation by 50-85% without reducing spike count. At 80 Hz, the optimal magnesium concentration was between 1.6 and 2.0 mM, reducing peak calcium concentration from 0.97 to 0.84 µM and preserving 80% of spikes. However, strong stress required a narrower protective window (0.4 mM at 80 Hz).

Timing of magnesium intervention was also crucial: pretreatment and immediate intervention achieved 100% protective efficacy, while delayed intervention resulted in significant spike loss.