A large number of toxic substances can produce impaired vision. Methyl alcohol causes sudden and permanent blindness. Chronic visual loss from optic neuritis develops in malnourished patients with a high tobacco consumption (Tobacco-alcohol amblyopia). The mechanism producing this disorder is uncertain, tobacco contains cyanide which in high dosage can dapnage the optic nerves. Pathology
Damage involves the papillomacular bundle within the optic nerves, chiasma and optic tracts. Retinal ganglion cells in the macular region are also affected. Clinical features
- The condition slowly develops over weeks.
- Vision in each eye becomes hazy and blurred.
- Colour vision (red/green discrimination) is involved early. s 1 s.. Macula Examination
- Bilateral involvement.
- Reduced visual acuity.
(a central field defect spreading from blind spot to macula and i most easily detected with a red target).
- Fundal examination is normal, though optic atrophy will occur eventually.
- Coexistent Wernicke Korsakoff syndrome or polyneuropathy are common. Treatment
Vitamin B supplementation, including B12, should be administered. B12 possesses the capacity for cyanide detoxification. Recovery is poor if visual loss is well established.
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