I’ve noticed warnings on a lot of poisonous substances if taken internally may cause blindness. I was curious by what mechanism does this actually take place. This question was spurred when I witnessed this guy accidentally spray carb cleaner in both his eyes, he started screaming within about two seconds and I got him water and flushed his eyes before he went to the hospital. I was reading the warnings on the back of the bottle when I noticed the caution about possible blindness if swallowed.
A quick wiki search does not answer the qustion, which I expect has different answers based on toxic substance (methanol, ‘wood alcohol’ destroys the optic nerve), but this is interesting, typical GI ingenuity
I stand to be corrected, but I don’t believe the specific mechanism by which methanol causes blindness is known.
What is known is that methanol is toxic specifically to two parts of the Central Nervous System - the retina (in the back of the eye) and the putamen (a structure deep in the brain involved with movement and motor learning, and likely also with learning in a more general sense).
When the body breaks down methanol, formic acid (like in ants) is formed. Formic acid screws up energy production by a mechanism that’s not been fully worked out (IIRC). It acts like a weak version of cyanide in this regard.
Since retina cells, like cells everywhere else, get their energy from their mitochondria, and perhaps also because the retina is VERY active metabolically, it’s believed that formic acid damage to the mitochondria underlies methanol-induced blindness. Things are made worse by the fact that when the mitochondria aren’t working properly, acid is formed. This is in addition to the acid load of the formic acid itself. Too much acid in cells leads to their death. So, several mechanisms, at least.
BTW, death from methanol poisoning, when it occurs, is usually due to too much acid in the blood (again from the formic acid itself, and from acid produced when the body’s mitochondria are damaged (i.e. anaerobic respiration)).
Of course, all this doesn’t explain why retina cells (and putamen cells) seem to be the only ones damaged by formic acid.
ETA: the breakdown of methanol to formic acid is carried out by the same enzyme that breaks down ethanol (i.e. booze). So, by giving ethanol to someone who’s ingested methanol, you compete for the body’s limited supply of that enzyme thereby decreasing production of the deadly formic acid from methanol.
I meant to say that organs from people who die from methanol poisoning can be, and are, successfully transplanted into other people. In other words, methanol poisoning is quite specific to the brain and leaves the other organs intact.