In Retinitis pigmentosa, following are true except:

D i.e. ERG normal - Typical retinitis pigmentosa/primary pigmentary retinal dystrophy is hereditary disorder affecting rodes more than cones and characterized by night blindness, tubular vision, annular (ring) scotoma bony spicule pigmentation, aeriolar attenuation and waxy pallor of optic discQ. - In Retinitis pigmentosa, "the symptoms are characteristic, the most prominnent being defecive vision in the dusk (night blindness, nyctalopiaQ). But there's no such option given here. Diplopia is not seen in RP, and central scotoma is very late feature. Peripheral field contraction is an early finding on perimetry, but definitely Ring scotoma is a more chacteristic feature and a relatively early one too. So, its best to go with "Ring scotoma" as the answer here. Electroretinogram indicates the activity of retina (especially rods and cones) and is subnormal or abnormal in diseases of retina e.g. retinitis pigmentosaQ. ERG has no role in assessing the functional integrity of optic nerve and so it can't be abnormal in optic neuritisQ. Causes of Ring Scotoma Tubular Vision - Retinitis - Retinitis pigmentosa Q pigmentosa - High myopia - High myopia - Primary open - Primary open angle glaucoma angle - Aphakic spectacle glaucoma correction - CRAO with - Panretinal sparing of photocoagulation centroretinal aery Retinitis Pigmentosa It affects the photoreceptors and retinal pigment epithelium (RPE) diffusely across entire fundus but begin with initial geographic involvement in either the periphery or the macula.