Makindo Medical Notes

Retinitis Pigmentosa (RP) is a group of inherited retinal degenerations causing progressive loss of photoreceptor cells. Patients first develop night blindness, then tunnel vision, and in advanced stages, complete blindness. When combined with hearing loss, it is known as Usher Syndrome. Early recognition and genetic testing are crucial for counselling and emerging therapies.

About

• Group of genetic disorders causing retinal degeneration.
• Rods affected first → night blindness, then cones → central vision loss.
• Inheritance: Autosomal recessive (most common), autosomal dominant, or X-linked.
• Progression varies widely depending on the underlying gene mutation.

🔬 Aetiology

• Caused by >60 gene mutations (e.g., rhodopsin, RPE65, USH2A).
• Disrupts photoreceptor metabolism and retinal pigment epithelium (RPE) function.
• Rod cells degenerate first → nyctalopia (night blindness).
• Some cases sporadic; male predominance due to X-linked forms.

🧬 Conditions Associated with RP

• Usher syndrome: RP + congenital or progressive deafness.
• Bardet-Biedl syndrome: RP + obesity, polydactyly, renal disease, learning disability.
• Refsum disease: RP + neuropathy, ataxia, anosmia (due to phytanic acid accumulation).
• Abetalipoproteinemia: RP + neuropathy, fat malabsorption, ataxia.
• Kearns-Sayre syndrome: RP + cardiac conduction block + external ophthalmoplegia.
• Alström syndrome: RP + obesity, diabetes, hearing loss.

🩺 Clinical Features

• Night Blindness (Nyctalopia): Early symptom due to rod dysfunction.
• Peripheral vision loss → Tunnel vision: Progressive field constriction.
• Fundus exam: Bone spicule pigmentation, attenuated arterioles, optic disc pallor.
• Photopsia: Flashes of light in dim environments.
• Gradual progression → eventual central vision loss in advanced stages.

🔎 Investigations

• Electroretinogram (ERG): Reduced/absent rod and cone responses (diagnostic).
• Genetic testing: Confirms mutation, informs prognosis, family planning, and gene therapy eligibility.
• Visual field testing: Maps tunnel vision progression.
• OCT: Retinal thinning, photoreceptor loss.
• Fundus photography: Documents spicule pigmentation & optic disc changes.

💊 Management

• Vitamin A palmitate: 15,000 IU/day may slow progression (monitor for toxicity).
• Gene therapy: Luxturna (voretigene neparvovec) for RPE65 mutations approved in some centres.
• Low vision aids: Magnifiers, screen readers, mobility training.
• Retinal prostheses: Argus II (“bionic eye”) under evaluation.
• Genetic counselling: For patients and families regarding inheritance.
• Supportive: Mobility training, guide dogs, counselling.

📊 Comparison: RP vs Other Retinal Degenerations

📈 Prognosis

• Progressive vision loss over decades.
• Peripheral vision lost first; central vision retained until later life.
• Some retain functional vision into mid-life; others progress rapidly depending on mutation.

🔑 Clinical Pearls

• Always ask about hearing loss → Usher syndrome.
• Bone spicule pigmentation on fundoscopy is diagnostic.
• Vitamin A should only be started under ophthalmologist guidance (risk of hepatotoxicity).
• Gene therapy is revolutionising care in specific subtypes (e.g., RPE65).

References

• Retinitis Pigmentosa - GeneReviews
• American Academy of Ophthalmology