Genetic mutations in mitochondrial DNA, vitamin depletion, alcohol and tobacco abuse, and use of certain drugs can cause derangements in efficient transport of mitochondria, which can cause a primary or secondary optic neuropathy. Nutritional optic neuropathies
A nutritional optic neuropathy may be present in a patient with obvious evidence of under-nutrition (weight loss and wasting). Months of depletion are usually necessary to deplete body stores of most nutrients. Undernourished patients often have many vitamin and nutrient deficiencies and have low serum protein levels. However, the optic neuropathy associated with pernicious anemia and vitamin B12 deficiency can even be seen in well-nourished individuals. Gastric bypass surgery may also cause a vitamin B12 deficiency from poor absorption. Patients who have nutritional optic neuropathy may notice that colors are not as vivid or bright as before and that the color red is washed out. This normally occurs in both eyes at the same time and is not associated with any eye pain. They might initially notice a blur or fog, followed by a drop in vision. While vision loss may be rapid, progression to blindness is unusual. These patients tend to have blind spots in the center of their vision with preserved peripheral vision. In most cases, the pupils continue to respond normally to light. Toxic optic neuropathies
The most recognized cause of toxic optic neuropathy is methanol poisoning. This can be a life-threatening event that normally accidentally occurs when the person mistook or substituted, methanol for ethyl alcohol.
The patient initially has nausea and vomiting, followed by respiratory distress, headache, and visual loss 18–48 hours after consumption. Without treatment, patients can go blind, and their pupils will dilate and stop reacting to light. Ethylene glycol, a component of automobile antifreeze, is a poison that is toxic to the whole body including the optic nerve. Consumption can be fatal, or recovery can occur with permanent neurologic and ophthalmologic deficits. While the visual loss is not very common, increased intracranial pressure can cause bilateral optic disc swelling from cerebral edema. A clue to the cause of intoxication is the presence of oxalate crystals in the urine. Like methanol intoxication, treatment is ethanol consumption. Ethambutol, a drug commonly used to treat tuberculosis, is notorious for causing toxic optic neuropathy. Patients with vision loss from ethambutol toxicity lose vision in both eyes equally. This initially presents with problems with colors (dyschromatopsia) and can leave central visual deficits. If vision loss occurs while using ethambutol, it would be best to discontinue this medication under a doctors supervision. Vision can improve slowly after discontinuing ethambutol but rarely returns to baseline. Amiodarone is an antiarrhythmic medication commonly used for abnormal heart rhythms (atrial or ventricular tachyarrhythmias). Most patients on this medication get corneal epithelial deposits, but this medication has also been controversially associated with NAION. Patients on amiodarone with new visual symptoms should be evaluated by an ophthalmologist. Tobacco exposure, most commonly through pipe and cigar smoking, can cause optic neuropathy.