A young adults presents with night blindness and tubular vision. On examination, IntraocularPressure was observed to be 18mm and the anterior segment was unremarkable. Fundoscopyshowed attenuation of aerioles and waxy pallor of the optic disc with bony corpuscles like spicules of pigmentation in mid peripheral retina. Ring scotomas were observed on perimetry. Which of thefollowing is the most likely diagnosis -

RETINITIS PIGMENTOSA This primary pigmentary retinal dystrophy is a hereditary disorder predominantly affecting the rods more than the cones. Inheritance Most common mode is autosomal recessive, followed by autosomal dominant. X-linked recessive is the least common. Incidence
It occurs in 5 persons per 1000 of the world population.
Age. It appears in the childhood and progresses slowly, often resulting in blindness in advanced middle age.
Race. No race is known to be exempt or prone to it.
Sex. Males are more commonly affected than females in a ratio of 3:2.
Laterality. Disease is almost invariably bilateral and both the eyes are equally affected. Clinical features (A) Visual symptoms 1. Night blindness. It is the characteristic feature and may present several years before the visible changes in the retina appear. It occurs due to degeneration of the rods. 2. Dark adaptation. Light threshold of the peripheral retina is increased; though the process of dark adaptation itself is not affected until very late. 3. Tubular vision occurs in advanced cases. 1. Retinal pigmentary changes. These are typicallyperivascular and resemble bone corpuscles in shape. Initially, these changes are found in the equatorial region only and later spread both anteriorly and posteriorly. 2. Retinal aerioles are attenuated (narrowed) and may become thread-like in late stages. 3. Optic disc becomes pale and waxy in later stages and ultimately consecutive optic atrophy occurs 4. Other associated changes which may be seen are colloid bodies, choroidal sclerosis, cystoid macular oedema, atrophic or cellophane maculopathy. (C) Visual field changes Annular or ring-shaped scotoma is a typical featurewhich corresponds to the degenerated equatorial zone of retina. As the disease progresses, scotoma increases anteriorly and posteriorly and ultimately only central vision is left (tubular vision). Eventually even this is also lost and the patient becomes blind. Ref : AK khurana 4/e page no 268.