Retinitis Pigmentosa

Rod photoreceptors, concentrated in the peripheral and mid-peripheral retina, mediate dim-light and peripheral vision, while cones, concentrated at the fovea, mediate central and color vision. Retinitis pigmentosa (RP) is a genetically heterogeneous group of inherited retinal dystrophies causing progressive rod-then-cone photoreceptor degeneration — the most common inherited retinal dystrophy overall.¹

RP results from mutations affecting photoreceptor structural proteins, phototransduction cascade components, or retinal pigment epithelium function, causing progressive rod photoreceptor apoptosis followed by secondary cone degeneration. Because rods dominate 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.¹

The classic presenting symptom is nyctalopia (night blindness), often noticed in adolescence or early adulthood, followed by gradual, progressive constriction of the peripheral visual field. Central acuity is typically preserved until later stages.

Key differentials include other inherited retinal dystrophies (cone-rod dystrophy, choroideremia, Stargardt disease), drug-induced retinal toxicity mimicking a pigmentary retinopathy, syndromic RP (Usher syndrome, Bardet-Biedl syndrome), and congenital stationary night blindness (non-progressive, stable ERG). Syndromic RP should always be actively considered given implications for systemic care.³

Diagnosis relies on characteristic fundus findings (bone-spicule pigment, arteriolar attenuation, waxy disc pallor), visual field constriction on perimetry, and electroretinography (ERG) showing markedly reduced or extinguished rod responses, often the earliest objective abnormality preceding visible fundus changes. Genetic testing increasingly confirms the specific causative gene, important for prognosis and treatment eligibility.¹ AI-assisted analysis of retinal imaging is an emerging, actively developing tool being investigated to support diagnosis and monitoring in inherited retinal disease, though it remains a developing area rather than established standard of care.²

There is no universally curative treatment for most forms of RP. 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 therapies (such as voretigene neparvovec for RPE65-associated disease) when applicable to the patient's genotype.¹ In syndromic RP, coordinated multidisciplinary care (audiology for Usher syndrome, nephrology and endocrinology for Bardet-Biedl syndrome) is essential.³

• Night blindness is typically the earliest symptom, often preceding detectable visual field constriction
• ERG can show marked rod response reduction before visible fundus changes appear, making it a key early diagnostic tool
• Genetic testing informs prognosis, counseling, and eligibility for gene-specific therapies¹
• Always screen for syndromic associations (Usher syndrome, Bardet-Biedl syndrome) given broader systemic care implications³
• Common pitfall: attributing night blindness solely to aging or refractive error
• Common pitfall: failing to screen for systemic features of syndromic RP