1215
Refers to hereditary retinal disease disorders characterized by degeneration of rod and cone photoreceptors.
It is characterized as the gradual progressive loss of rod, and subsequently cone, photoreceptors, resulting in vision loss.
Photoreceptor loss is accompanied by inner retinal re-organization and atrophy of the retinal pigment epithelium.
Patients typically experience a defective dark adaptation, followed by progressive bilateral reduction of the peripheral vision field.
Over time the field loss progresses into the macula, and central vision is lost together with acuity.
Worldwide prevalence 1 in 4000, indicating more than 1 million affected people.
About 30-40% of cases are inherited as autosomal dominant , 50-60% autosomal recessive or 5-15% X-linked.
Patients with autosomal recessive and X-linked forms of inheritance progress most rapidly.
All isolated cases are assumed to be autosomal recessive, although new mutations, uniparental isodisomy or X-linked mutations can occur.
The autosomal dominant retinitis pigmentosa progresses more slowly and accounts for 15-20% of all cases and is caused by approximately 30 genes, of which the proline-to-histidine mutation a codon 23 missense rhodopsin (RHO) gene mutations is most prevalent in the US.
Usually confined to the eye but 20-30% of patients have associated non-ocular disease.
Usher’s syndrome is a disease of retinitis pigmentosa and hearing impairment, accounting for 20-40% of cases of recessive disease or about 10-20% of all cases.
Hearing loss can be profound and associated with vestibular ataxia, Usher’s syndrome type I, or mild to moderate and non progressive in type II disease.
Yype III Usher’s syndrome is associated with normal hearing at birth and with later years gradual hearing loss can occur with type III Usher’s syndrome.
At least 11 gene alterations associated with Usher’s syndrome leading to type I, II, or III type Usher’s syndrome.
Associated with Bardet-Biedl syndrome in which other processes are present including obesity, impaired mentation, polydactyly, hypogonadism, and renal abnormalities of calyceal cysts or calyceal clubbing, and renal failure.
Bardet-Biedl syndrome accounts for 5-6% of cases of retinitis
No approved medical therapy is available.
In most advanced cases the Argus II Retinal Prosthesis System may avoid some functional improvement.