Retinitis Pigmentosa

Overview

Retinitis pigmentosa (RP) is a genetically heterogeneous group of inherited retinal dystrophies characterized by progressive degeneration of rod photoreceptors followed by cone photoreceptors, leading to night blindness and progressive peripheral visual field loss, with central vision typically preserved until later in the disease course. RP may occur as an isolated ocular condition (non-syndromic) or as part of a broader systemic syndrome.

Epidemiology & Risk Factors

RP is the most common inherited retinal dystrophy, with inheritance patterns including autosomal dominant, autosomal recessive, X-linked, and mitochondrial forms, reflecting mutations in more than 80 identified genes affecting photoreceptor structure, phototransduction, or the visual cycle. Syndromic forms account for a meaningful minority of cases; Usher syndrome (RP with sensorineural hearing loss) and Bardet-Biedl syndrome (RP with obesity, polydactyly, renal anomalies, and other systemic features) are among the most clinically important syndromic associations to recognize, given their implications for systemic screening and genetic counseling.³

Pathophysiology

RP results from mutations affecting photoreceptor structural proteins, phototransduction cascade components, or retinal pigment epithelium function, ultimately causing progressive rod photoreceptor apoptosis followed by secondary cone degeneration. Because rods are concentrated in the peripheral and mid-peripheral retina and mediate dim-light vision, rod-predominant early degeneration explains the classic early symptom of night blindness and peripheral field loss, with central, cone-mediated vision relatively preserved until later stages when cone degeneration becomes more significant.

Clinical Presentation

The classic presenting symptom is nyctalopia (night blindness), often noticed first in adolescence or early adulthood, followed by gradual, progressive constriction of the peripheral visual field ("tunnel vision"). Central visual acuity is typically preserved until later in the disease course, when cone involvement becomes significant, though some patients develop earlier central vision loss from associated cystoid macular edema or epiretinal membrane.

Exam Findings

• Bone-spicule pigmentary deposits in the mid-peripheral retina, the classic fundoscopic finding
• Attenuated (narrowed) retinal arterioles
• Waxy pallor of the optic disc
• Posterior subcapsular cataract, a common associated finding
• Constricted visual fields on formal perimetry, corresponding to the degree of peripheral photoreceptor loss
• Markedly reduced or extinguished rod and (later) cone responses on electroretinography (ERG), often the earliest objective abnormality, preceding visible fundus changes
• In syndromic RP such as Bardet-Biedl syndrome, associated systemic findings (obesity, polydactyly, renal anomalies, developmental delay) should be actively sought³

Differential Diagnosis

• Other inherited retinal dystrophies (cone-rod dystrophy, choroideremia, Stargardt disease), distinguished by the pattern and sequence of photoreceptor involvement on ERG and imaging
• Drug-induced retinal toxicity (e.g., certain antimalarial or phenothiazine medications) mimicking a pigmentary retinopathy
• Syndromic RP (Usher syndrome, Bardet-Biedl syndrome, and others), which should be actively considered and screened for given implications for systemic care and genetic counseling³
• Congenital stationary night blindness (non-progressive, distinguished by a stable rather than progressively worsening ERG and clinical course)

Management

Diagnosis relies on the combination of characteristic fundus findings, visual field constriction on perimetry, and ERG demonstrating markedly reduced or extinguished rod responses; genetic testing is increasingly used to confirm the specific causative gene, which is important for prognosis, genetic counseling, and eligibility for gene-specific therapies (such as voretigene neparvovec for RPE65-associated disease).¹

There is currently no universally curative treatment for most forms of RP, and management focuses on supportive measures: low-vision rehabilitation, genetic counseling, management of associated complications (cataract surgery when visually significant, treatment of cystoid macular edema when present), and referral for gene-specific or emerging therapies when applicable to the patient's genotype.¹ Artificial intelligence-assisted analysis of retinal imaging is an emerging tool being investigated to support diagnosis, phenotype-genotype correlation, and disease monitoring in inherited retinal diseases including RP, though this remains a developing area rather than established standard of care.² In syndromic RP, coordinated multidisciplinary care (audiology for Usher syndrome, nephrology and endocrinology for Bardet-Biedl syndrome) is essential.³

Complications

• Progressive, eventually severe peripheral visual field constriction, with legal blindness from field loss possible even when central acuity is preserved
• Posterior subcapsular cataract requiring surgical management
• Cystoid macular edema contributing to central vision loss in a subset of patients
• Psychosocial impact of progressive, currently largely untreatable vision loss, warranting attention to patient support and low-vision resources
• In syndromic forms, associated systemic complications requiring coordinated multidisciplinary management³

Clinical Pearls

• Night blindness (nyctalopia) is typically the earliest symptom, often preceding detectable visual field constriction
• ERG can show marked rod (and later cone) response reduction before visible fundus changes are apparent, making it a key early diagnostic tool
• Genetic testing helps confirm diagnosis, informs prognosis and counseling, and determines eligibility for gene-specific therapies where available¹
• Always consider and screen for syndromic associations (Usher syndrome, Bardet-Biedl syndrome) given implications for hearing, renal, and other systemic care³
• AI-assisted imaging analysis is an emerging, actively developing adjunct for diagnosis and monitoring in inherited retinal disease, not yet an established standalone standard of care²

Common Pitfalls

• Attributing night blindness solely to normal aging or refractive error without considering RP or another inherited retinal dystrophy
• Failing to screen for systemic features of syndromic RP (hearing loss, obesity, polydactyly, renal disease), missing an important diagnosis with broader management implications
• Treating RP as a single, uniform disease rather than a genetically heterogeneous group with variable inheritance, prognosis, and treatment eligibility
• Overpromising currently available treatments as curative, rather than accurately conveying the current state of supportive and gene-specific therapy
• Overlooking genetic testing and counseling, which are increasingly central to modern RP management, prognosis, and family planning discussions