retinitis pigmentosa

retinitis pigmentosa
Name	Retinitis pigmentosa
Synonyms	RP
Field	Ophthalmology
Symptoms	Night blindness, peripheral vision loss, photopsia
Complications	Macular edema, Cataract, Glaucoma
Onset	Variable, often childhood to early adulthood
Duration	Lifelong, progressive
Types	Non-syndromic, syndromic (e.g., Usher syndrome)
Causes	Genetic mutations
Risks	Family history
Diagnosis	Electroretinography, Visual field test, Fundus photography
Differential	Choroideremia, Gyrate atrophy
Prevention	Genetic counseling
Treatment	Supportive care, Vitamin A palmitate, low vision aids
Medication	Acetazolamide (for edema)
Prognosis	Variable, often leads to legal blindness
Frequency	~1 in 4,000

retinitis pigmentosa is a group of inherited retinal dystrophies characterized by progressive photoreceptor cell death. It is a leading cause of inherited blindness worldwide, with significant clinical heterogeneity. The condition typically manifests with nyctalopia and gradual loss of peripheral vision, often progressing toward central vision loss over decades.

Signs and symptoms

The earliest symptom is typically difficulty with night vision and dark adaptation, known as nyctalopia. Patients often report progressive loss of peripheral vision, described as tunnel vision, which can lead to frequent collisions with objects. As the disease advances, involvement of the macula can cause decreased central acuity, light flashes, and impaired color discrimination. Common associated findings on examination include posterior subcapsular cataracts and Cystoid macular edema, which can further compromise vision.

Causes

The disorder is almost exclusively genetic, following autosomal recessive, autosomal dominant, or X-linked inheritance patterns. Over 100 different genes have been implicated, including RHO (rhodopsin), RPGR (retinitis pigmentosa GTPase regulator), and USH2A (usherin). Mutations in these genes disrupt critical pathways in the photoreceptor or retinal pigment epithelium (RPE). Syndromic forms occur, most notably Usher syndrome, which combines the condition with hearing loss, and Bardet-Biedl syndrome.

Pathophysiology

The primary pathology is the degeneration of rod photoreceptors, which are responsible for low-light vision, followed later by cone photoreceptor loss. Mutations lead to apoptotic cell death through mechanisms such as protein misfolding, disrupted phototransduction cascade, or impaired phagocytosis by the RPE. This results in characteristic intraretinal pigment migration visible on fundoscopy. The retinal ganglion cells and optic nerve are typically preserved until late stages.

Diagnosis

Diagnosis relies on a combination of clinical history, fundoscopic examination, and specialized testing. Key diagnostic tools include full-field electroretinography (ERG), which shows severely reduced or non-detectable rod and cone responses. Automated perimetry demonstrates progressive constriction of the peripheral visual field. Spectral-domain OCT can reveal thinning of the outer nuclear layer and loss of the ellipsoid zone. Genetic testing, often via panels or whole exome sequencing, is increasingly used for confirmation and prognosis.

Management

There is no cure; management focuses on slowing progression, treating complications, and rehabilitation. Some patients may benefit from high-dose vitamin A palmitate supplementation, though this is controversial and requires monitoring for toxicity. Oral acetazolamide can be effective for treating associated macular edema. Low vision rehabilitation includes training with optical aids, screen readers, and orientation and mobility training. Regular monitoring for cataracts and secondary glaucoma is essential. Research into voretigene neparvovec and retinal prostheses like the Argus II offers future therapeutic directions.

Prognosis

The rate of progression and final visual outcome are highly variable, depending on the genetic subtype and mode of inheritance. Most individuals experience progressive visual field loss, with many reaching legal blindness by middle age. Central vision may be preserved until later stages, but eventual macular involvement is common. The development of cataracts or glaucoma can accelerate visual decline. Life expectancy is generally unaffected in non-syndromic cases, but syndromic forms like Usher syndrome carry additional systemic implications.

Epidemiology

It is one of the most common inherited retinal diseases, with a worldwide prevalence of approximately 1 in 4,000 individuals. It affects all ethnic groups and both sexes, though the X-linked forms predominantly affect males. The prevalence of specific genetic mutations varies by population; for instance, mutations in the RHO gene are common in autosomal dominant cases in North American cohorts. Syndromic forms account for 20-30% of cases, with Usher syndrome being the most frequent association.

Category:Genetic disorders Category:Eye diseases