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Inherited retinal dystrophies
Inherited retinal dystrophies differ by the cells affected first: in retinitis pigmentosa the rods are affected first — night blindness and a narrow field — and in macular dystrophies such as Stargardt and Best central vision is affected early; diagnosis rests on the fundus, ERG, EOG and genetic testing, and some diseases already have gene therapy.
Why it matters in the exam
Retinitis pigmentosa: night blindness in childhood or young adulthood, a visual field that shrinks to a "tunnel", and in the fundus — "bone spicule" pigment in the periphery, thin arteries and a waxy pale disc. The ERG is markedly reduced, rods more than cones. Inheritance: dominant, recessive or X-linked — the last being the most severe. Treatable complications: cystoid macular oedema (responds to carbonic anhydrase inhibitors) and posterior subcapsular cataract. Voretigene neparvovec is an approved gene therapy for biallelic RPE65 mutation.
Syndromes with RP: Usher — congenital deafness with RP, the commonest syndrome; Bardet-Biedl — obesity, polydactyly, hypogonadism and kidney disease; Refsum — phytanic acid accumulation, treated by diet; abetalipoproteinaemia — vitamin E and A deficiency, treated with supplements; Kearns-Sayre — a mitochondrial disease with progressive external ophthalmoplegia, ptosis and heart block. In a child with nystagmus and blindness from birth who presses on the eyes, think of Leber congenital amaurosis.
Stargardt disease — the commonest macular dystrophy in young people, the ABCA4 gene, recessive inheritance: reduced central vision at school age, a "beaten bronze" macula and yellowish flecks, and a "dark choroid" on angiography; avoiding vitamin A supplements is advised. Best disease — the BEST1 gene, dominant inheritance, an "egg yolk" lesion at the macula; a reduced EOG (Arden ratio below 1.5) with a normal ERG — a combination that identifies the disease. Cone dystrophy — photophobia, impaired colour vision and reduced acuity. Choroideremia — X-linked, the CHM gene.
Key points
- RP: night blindness, tunnel field, bone spicules, reduced ERG.
- Usher: RP with deafness.
- Stargardt: ABCA4, central loss in a child, dark choroid.
- Best: egg yolk, reduced EOG, normal ERG.
- RPE65 → voretigene neparvovec.
Summary table
| Disease | Gene or inheritance | Sign | Diagnostic test |
|---|---|---|---|
| Retinitis pigmentosa | AD, AR or X | Night blindness, bone spicules | Markedly reduced ERG |
| Stargardt | ABCA4, recessive | "Beaten bronze" macula, flecks | Dark choroid, genetics |
| Best | BEST1, dominant | "Egg yolk" lesion | Reduced EOG with normal ERG |
| Usher | Recessive | RP with deafness | Hearing and ERG |
| Leber congenital amaurosis | RPE65, CEP290 and others | Blindness and nystagmus from birth | Almost flat ERG |
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Sources
- AAO Clinical Statement: Recommendations on Clinical Assessment of Patients with Inherited Retinal Degenerations, 2022 — Genetic testing and follow-up
- AAO Basic and Clinical Science Course, Section 12: Retina and Vitreous, 2024-2025 — Hereditary retinal and choroidal disease
- Kanski's Clinical Ophthalmology, 9th edition (2020) — Hereditary fundus dystrophies
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.