Colourblindess is caused by

Ans. b (Ethambutol). (Ref. Katzung 12th/Chapter 47)Hypersensitivity to ethambutol is rare. The most common serious adverse event is retrobulbar neuritis, resulting in loss of visual acuity and red-green color blindness. This dose-related adverse effect is more likely to occur at dosages of 25 mg/kg/d continued for several months. At 15 mg/kg/d or less, visual disturbances are very rare. Periodic visual acuity testing is desirable if the 25 mg/kg/d dosage is used. Ethambutol is relatively contraindicated in children too young to permit assessment of visual acuity and red-green color discrimination.Drugs causing color vision alterationDrugs causing cataractDrugs causing retinopathyBarbituratesBusulfanChloroquineDigoxin (yellow vision)SteroidPhenothiazidesEthambutol (red-green blindness)PhenothiazidesDEC (anti-filarial)Sildenafil citrate (blue-green blindness)Miotics Thioridazone, thiazidesGold SulfonamidesChloroquine SYSTEMIC DRUGS:ADVERSE OCULAR EFFECTSOxygen> Retinopathy of prematurity.0Digitalis> Disturbances of color vision (yellow vision), scotomas, photopsia.Quinidine> Optic neuritis (rare).Thiazides> Xanthopsia (yellow vision), myopia.Carbonic anhydrase inhibitors> Ocular hypotony, transient myopia.Amiodarone> Corneal deposits.Anticholinergic agents> Risk of angle closure glaucoma due to mydriasis. Blurring of vision due to cycloplegia.Barbiturates> Extraocular muscle palsies with diplopia, ptosis, cortical blindness.Chloral hydrate> Diplopia, ptosis, miosis.Phenothiazines> Deposits of pigment in conjunctiva, cornea, lens and retina. Oculogyric crises.Amphetamines> Widening of palpebral fissure. Dilation of pupil, paralysis of ciliary muscle with loss of accommodation.Monoamine oxidase (MAO) inhibitors> Nystagmus, extraocular muscle palsies, optic atrophy.Tricyclic agents> Dilation of pupil (risk of angle closure glaucoma)0, cycloplegia.Phenytoin> Nystagmus, diplopia,0 ptosis, slight blurring of vision (rare).Neostigmine> Nystagmus, miosis.Morphine> Miosis.Haloperidol> Capsular cataract.Lithium carbonate> Exophthalmos, oculogyric crisis.Diazepam> Nystagmus.Corticosteroids> Cataract (posterior subcapsular), local immunologic suppression, causing susceptibility to viral (herpes simplex), bacterial, and fungal infections; steroid induced glaucomaFemale sex hormones> Retinal artery occlusion, retinal vein occlusion, papilledema, ocular palsies with diplopia, nystagmus, optic neuropathy, retinal vasculitis, scotomas, migraine, mydriasis and cycloplegia, and macular edema.Chloramphenicol> Optic neuritis and atrophy.Rifabutin> Uveitis.Streptomycin> Optic neuritis.Tetracycline> Pseudotumor cerebri, transient myopiaChloroquine> Macular changes, central scotomas, pigmentary degeneration of the retina, chloroquine keratopathy, ocular palsies, ptosis, ERG depression.lodochlorhydroxyquin> Optic atrophy.Sulfonamides> Stevens Johnson syndrome.Ethambutol> Optic neuritis and atrophy.Isoniazid> Optic neuritis and atrophy/ color blindness.Gold salts> Deposits in the cornea and conjunctiva.Lead> Optic atrophy, papilledema, ocular palsies.Penicillamine> Ocular pemphigoid, optic neuritis, ocular myasthenia.Chlorpropamide> Transient change in refractive error, diplopia, Stevens Johnson syndrome.Vitamin A> Papilledema, retinal hemorrhages, loss of eyebrows and eyelashes, nystagmus, diplopia, blurring of vision.Vitamin D> Band shaped keratopathy.Salicylates> Nystagmus, retinal hemorrhages, cortical blindness (rare).Indomethacin> Corneal deposits.Phenylbutazone> Retinal hemorrhages