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Retinitis Pigmentosa and Inherited Chorioretinal Dystrophies

CHRONIC — Retina

Symptoms

  • nyctalopia (night blindness): the earliest and most consistent symptom
  • tunnel vision: progressive loss of peripheral visual field over decades
  • photophobia: sensitivity to bright lights, often appearing as cones become involved
  • central vision loss: typically occurs late in the disease course
  • shimmering lights (photopsias): common in the mid-peripheral field

Clinical Findings

Classic fundus triad

  • bone-spicule pigmentation: pigment clumps along vessels in the mid-periphery
  • attenuated arterioles: threadlike narrowing of the retinal blood vessels
  • waxy disc pallor: a yellowish-pale appearance of the optic nerve head

Imaging & electrophysiology

  • full-field erg: defining test; rod responses are extinguished or severely reduced
  • oct: shows loss of the "ellipsoid zone" (photoreceptors) starting from the periphery
  • autofuorescence: often shows a "hyperautofluorescent ring" surrounding the macula

Associated ocular signs

  • posterior subcapsular cataract: nearly universal in adult patients
  • cystoid macular edema (cme): present in 20–40% of cases; a treatable cause of blurring
  • vitreous cells: fine pigmented "dust" often visible even before bone spicules

Etiology

Pathophysiology

  • primary degeneration of rod photoreceptors followed by secondary cone loss

Genetics

  • extremely heterogeneous: >100 causative genes identified
  • inheritance: autosomal recessive (most common), dominant, or x-linked (most severe)

Syndromic forms

  • usher syndrome: rp + sensorineural hearing loss
  • bardet-biedl: rp + obesity + polydactyly + renal issues
  • kearns-sayre: rp + external ophthalmoplegia + cardiac heart block (potentially fatal)

Red Flags

  • mandatory usher screen: every pediatric patient with RP needs audiology testing
  • treatable blurring: check for cme on oct; it often responds to topical drops
  • kearns-sayre: any patient with ptosis/eye movement limits needs an urgent ekg
  • vitamin a safety: avoid in stargardt/abca4 disease as it accelerates vision loss

Investigations

Clinical & functional

  • goldmann visual fields: superior to automated perimetry for tracking the ring scotoma
  • baseline erg: to distinguish rp from stationary night blindness

Laboratory & genetic

  • genetic testing: now standard of care to identify candidates for gene therapy
  • syphilis serology: "pseudo-rp" can be caused by late-stage syphilis
  • metabolic screening: phytanic acid (refsum) or lipid panels if syndromic signs exist

Treatment

Medical management

  • topical dorzolamide (cai): first-line treatment for cystoid macular edema
  • vitamin a palmitate (15,000 iu): controversial; may slow progression in non-smokers
  • gene therapy: voretigene neparvovec (luxturna) is fda-approved for biallelic rpe65

Surgical & supportive

  • cataract surgery: can provide significant improvement if the macula is functional
  • tinted lenses: help with photophobia and improve contrast in bright environments
  • low-vision aids: magnifiers, telescopes, and digital assistive technology

Clinical Pearl

Ring scotoma, bone spicules, attenuated vessels, and waxy disc pallor on exam with extinguished ERG is classic RP — but always obtain genetic testing, because gene therapy for RPE65 (Luxturna) is now a reality.

Differential Diagnosis

  • • syphilis (the "great masquerader")
  • • cancer-associated retinopathy (car)
  • • phenothiazine toxicity (thioridazine/chlorpromazine)
  • • congenital rubella (salt-and-pepper fundus, but normal erg)

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