A patient with rheumatoid arthritis is being treated with NSAIDs (diclofenac) for joint pain for a long time. Now the patient presents with reduced visual acuity and loss of colour vision. What is your likely diagnosis?

Ans: C (Optic neuritis) Ref: Kanski's Clinical Ophthalmology. Internet Sources and Parson's Opthalmology and A Textbook of Ophthalmology By Ahmed, pg 364Explanation:Diclofenac can rarely cause optic neuritis (in 0.12% patients).Colour vision is the function of optic nerve. So in any optic nerve pathology, colour vision is the earliest top get affected.In glaucomas and cataract, colour vision is usually unaffected or affected very late.Causes of Colour BlindnessInherited Diseaseso Cone dystrophy.o Cone-rod dystrophy.o Achromatopsia.o Blue cone monochromatism.o Leber's congenital amaurosis.o Retinitis pigmentosa.Optic NeuritisSenile macular degeneration - Most Commonly acquired cause.Pigmentary dystrophy of retina.Glaucoma.Myopia.Toxic amblyopia.Chorioretinitis.Drug induced:o Chlo require.o Indomethacin.o Phosphodiesterase type 5 inhibitors such as sildenafil.o Digoxin.o Interferon alfa.o Ethambutol.o Metronidazole.Shaken baby syndrome.Diabetic retinopathy.Vitamin A deficiency.