Impairment of vision due to methyl alcohol intoxication is abrupt in onset. And if visual functions return, it generally does so in the first six days.
- Large, symmetrical and central scotomas
- Decreased pupillary response to light.
This has prognostic significance. No patient with normally reactive pupils has suffered permanent visual loss. However, the decreased pupillary reaction may occur in patients who have had a complete recovery.
The mechanism of selective involvement of the optic nerve in methanol toxicity remains unknown.
Other drugs with proven but less devastating toxic effects on the optic nerve include
- Sulfonamides Digitalis
- Heavy metals
These above features are accompanied by
- Subnormal temperature
Despite severe acidosis, “Kussmaul Respiration” (i.e. intense hyperventilation or air hunger) is not common because of respiratory depression caused by intoxication. In moribund patients, the respiration is slow, shallow, gasping and “fish–mouth”.
Coma follows unconsciousness and death occurs from cardiorespiratory failure and is almost always preceded by blindness.
- Delirium and coma may last for 2–3 days.
- Coma induced by methanol is longer in its onset and also lasts longer than in thanol.
- Although recovery is common from drunkenness from ethanol, it is nearly always fatal in case of methanol poisoning.