Any insight on the effects of magnesium powder flash on the retina, and specifically how long of exposure causes permanent damage? thank you!

Can Damage vision: Exceedingly bright light light a powder flash can burn the retina and cause a permanent scotoma (black spot) in the vision. Eye protection is recommended whenever working with this substance. The longer the exposure, the more likely the retina is to sustain a burn. Very short exposures will leave an afterimage, which can last hours or days, but won't cause permanent damage.