Toxic damages & atrophy of optic nerve Topic 48
=conditions where exogenous poisons or endogenous (toxins rarely) damage the optic nerve
1. Tobacco Amblyopia
- Heavy smokers, drinker + deficient in proteins & vitamin B
- It is called tobacco- alcohol- amblyopia as they form a complex
Pathogenesis : (main issue is cyanide increase)
- Excessive smoking raises CN levels & excessive drinking lower sulphur rich proteins needed to detoxify thus double effect
- Ganglion cells are degenerated (near macular esp) and then degeneration of Papillo-macular bundle in the nerve
Clinical features :
- 40-60 years old , slow, bilateral visual loss
- Visual field = bilateral cenrocaecal scotomas
- Fundus can be normal
Treated with complete alcohol and smoking cessation with good prognosis
Ethyl alcohol (drinkers but not smokers, chronic)
- Similar to above but worse prognosis
Methyl alcohol amblyopia
- Acute reactions as methanol is oxidised to formaldehyde and formic acid with caused oedema + degeneration of ganglion cells of the retina → complete blindness !!
- Clinically: headache, dizziness, abdominal pain, vomiting etc.
- Characteristics odour due to formaldehyde in breath or sweat
- Feature: almost complete blindness + mild disc oedema + narrow blood vessels→ might end with optic atrophy
- Treatment :gastric lavage , fight acidosis with soda bicarb
- Ethyl alcohol prevents formaldehyde production
- dialysis to help clear the alcohol& formaldehyde from body
- Prognosis : poor , blindness often occurs , even death
Quinine
-drug may cause near total blindness in susceptible patients and deafness and tinnitus may be associated with it pupils are fixed and dilated, retinal oedema +disc pallor+ extreme thinning of retina vessels and low visual field
Ethambutol Amblyopia
- Frequently used against TB and it usually occurs in patients with associated alcoholism and diabetes
- Optic neuritis with typical central Scotoma + Papillitis
Papillitis + attenuation of vessels+ central stroma seen in patient treated with Ethambutol which is a TB medication + maculopathy (oedema of the macula)
Optic atrophy
Degeneration of the optic nerve from damage to anterior visual system (retinal ganglions to geniculate) they are divided into
- 1. Primary simple = due to lesions near optic disc not from papilloedema: m. Sclerosis, Retrobulbar neuritis, Leber’s and other hereditary types , intracranial tumours, traumatic injury and toxic amblyopias Minor changes occurs with disc appearing chalky white, edges are sharp, normal vessels, cribrosa seen.