Retinitis Pigmentosa (Typical)
It is an inherited retinal dystrophy characterized by diffuse progressive dysfunction of the rod photoreceptors and subsequent degeneration of cone photoreceptors and the retinal pigment epithelium, usually bilateral and symmetrical.
Modes of inheritance:
Autosomal dominant- best prognosis
Autosomal recessive- most common
X-Linked Recessive- worst prognosis
Signs and Associations:
Functional signs:
Night blindness/ Nyctalopia - earliest
Photophobia
Visual acuity preserved till late stages
Visual Field:
Peripheral vision involvement—> Ring shaped scotoma—> Tunnel vision
Associated with keratoconus, myopia, posterior subcapsular cataract, open angle glaucoma, vitreous cells and vitreous detachment
Fundus:
Classical Triad:
Pigmentary deposits resembling bony spicules, initially in peripheral retina
Attenuation of retinal vessels
Waxy pallor of optic disc
Depigmentation and atrophy of the RPE
Macula- epiretinal membrane, cystoid macular edema, macular atrophy
Bony spicules:
Bony spicules contain pigments released by the RPE and they form only in areas of the retina where photoreceptors are missing.
In RP, the inner retina is left intact until late stages of the disease. In these cases, since the outer retina has been lost, the retinal vessels located at outer plexiform layer in the inner retina come in direct contact with the RPE.
This RPE-Retinal vessels contact causes miigration of the RPE cells occurs without fail along these vascular networks of the inner retina, starting in the interstitial space and then cuffing the vessels.
This pattern mimics the spicules in the bone and hence termed as ‘bony spicules’.
ERG:
Diminution of a and b wave amplitudes
Scotopic predominates over photopic
Syndromes commonly associated: Usher Syndrome, Bardet Biedel Syndrome, Bassen Kortzweig Disease, Refsum Disease etc.
Image from Rajan Eye Care Hospital