RETINITIS PIGMENTOSA

• Primary pigmentary retinal dystrophy predominantly affects rods more than cones
• Sporadic >Autosomal recessive > Autosomal dominant > X-linked recessive
• X-linked cases are most severe
• Incidence 5 per 1000 people
• Males more affected
• Invariably bilateral 

Signs and Symptoms 

• Night blindness or nyctalopia is the characteristic feature — due to degeneration of rods
• Light threshold of peripheral retina is increased. Dark adaptation is not affected until very late
• Tubular vision in advanced cases
• Retinal pigmentary changes resembling bone corpuscles — typically perivascular
• Attenuation (narrowing) of retinal arterioles
• Optic disc becomes pale and waxy — consecutive optic atrophy
• Annular or ring shaped scotoma is the typical visual field defect
• Later only central vision is left (tubular vision)
• ERG is subnormal or abolished (scotopic affected before photopic; b wave affected before a wave)
• EOG – absence of light peak 

Syndromes associated with Retinitis pigmentosa

• Refsum’s syndrome: peripheral neuropathy, cerebellar ataxia
• Usher’s syndrome: labyrinthine deafness
• Laurence-Moon-Biedl: syndromeobesity, hypogenitalism, polydactyly, mental deficiency
• Cockayne’s syndrome: progressive infantile deafness, dwarfism, mental retardation, nystagmus, ataxia
• Hallgren’s syndrome: vestibulo-cerebellar ataxia, congenital deafness, mental deficiency
• Friedrich’s ataxia, Kearns-Sayre syndrome 

Atypical forms of retinitis pigmentosa

• Retinitis pigmentosa sine pigmento: all features of RP except visible pigmentary changes in the fundus
• Sectorial RP: involvement of one sector of retina
• Pericentric RP: pigmentary changes are confined to an area immediately around macula
• Retinitis punctata albescens: innumerable discrete white dots scattered over the fundus without pigmentary changes