Methanol toxicity causes blindness due to the formation of:-

Methyl Alcohol (Methanol) It is metabolized to formaldehyde (by alcohol dehydrogenase) and finally to formic acid (by aldehyde dehydrogenase). Accumulation of formic acid may result in lactic acidosis (high anion gap metabolic acidosis), blindness and death. Specific toxicity of formic acid is retinal damage leading to blindness. Fomepizole (4-Methylpyrazole) is drug of choice for methanol poisoning because it is a specific inhibitor of alcohol dehydrogenase. Folic acid or folinic acid can also be used because folate dependent systems are responsible for conversion of formic acid to CO2.