Question
A 22-year-old male with a positive family history of inherited retinal degeneration presents with gradually worsening vision, especially in dim light. On ophthalmoscopic examination, which of the following findings most strongly indicates this condition?
A. Yellowish deposits giving a “fried-egg” look near the central retina
B. Ring-shaped macular pigment changes with central sparing
C. Dark, star-like pigment clumps in the outer (peripheral) retina
D. Lipid deposits with bleeding changes mainly in the macular region
E. Diffuse abnormal new vessel formation beneath the retina
Answer
Dark, star-like pigment clumps in the peripheral retina
Detailed discussion for MRCP
Core concept
Retinitis pigmentosa (RP) is a group of inherited retinal dystrophies characterized by progressive degeneration of photoreceptors, primarily rods first → cones later.
Pathophysiology (high-yield)
- Initial degeneration: rod photoreceptors (peripheral retina)
- Later: cone involvement (central vision)
- Mechanism:
- Genetic mutations (e.g., rhodopsin, PDE6, peripherin)
- Apoptosis of photoreceptors
- Migration of retinal pigment epithelium (RPE) cells → produces pigmentation
Classic triad of RP (VERY IMPORTANT FOR MRCP)
- Bone spicule pigmentation (peripheral retina)
- Attenuated retinal vessels
- Waxy pallor of optic disc
Fundoscopy hallmark
- Black bone spicule-shaped pigmentation in the peripheral retina
- Due to RPE cell migration into the neural retina
Clinical features (stepwise progression)
- Night blindness (nyctalopia) → earliest symptom
- Peripheral visual field loss → tunnel vision
- Central vision preserved until late
- Eventually → complete blindness
Visual field defect
- Concentric peripheral loss → “tunnel vision”
Associated syndromes (very high yield)
- Usher syndrome → RP + sensorineural deafness
- Refsum disease → RP + ataxia + neuropathy + ichthyosis
- Bardet-Biedl syndrome → RP + obesity + polydactyly + hypogonadism
- Abetalipoproteinaemia → fat malabsorption + RP
- Kearns-Sayre syndrome → mitochondrial disorder
Genetics (exam favourite)
- Autosomal dominant (mild)
- Autosomal recessive (moderate)
- X-linked (severe, early onset)
Differentiating from other options
Stargardt disease
- “Scrambled egg” / pisciform flecks
- Central vision loss
- Macular involvement
Hydroxychloroquine toxicity
- Bull’s eye maculopathy
- Central ring of RPE damage
Age-related macular degeneration
- Drusen + hemorrhage
- Central retina (macula)
Choroidal neovascularization
- Seen in wet AMD, myopia
- Not typical for RP
Investigations
- Electroretinography (ERG) → reduced/absent rod response (diagnostic)
- Visual fields → peripheral constriction
- OCT → photoreceptor layer thinning
- Genetic testing
Management
- No cure
- Supportive:
- Vitamin A (controversial but exam-relevant)
- Low vision aids
- Genetic counselling
- Emerging:
- Gene therapy (e.g., RPE65 mutation → voretigene neparvovec)
Cheat Sheet
- RP = rod degeneration → night blindness first
- Fundus = bone spicule pigmentation (periphery)
- Visual field = tunnel vision
- Triad:
- Bone spicules
- Vessel attenuation
- Waxy disc pallor
- Associations:
- Usher
- Refsum
- Bardet-Biedl
- Investigation = ERG ↓ rod response
Flash Cards
Q: Earliest symptom of retinitis pigmentosa?
A: Night blindness
Explanation: Rods affected first.
Q: Classic fundoscopic finding in RP?
A: Bone spicule pigmentation
Explanation: Due to RPE migration.
Q: Which photoreceptors are affected first in RP?
A: Rods
Explanation: Peripheral retina involvement.
Q: Visual field defect in RP?
A: Tunnel vision
Explanation: Progressive peripheral loss.
Q: Syndrome: RP + deafness?
A: Usher syndrome
Explanation: Most common syndromic association.
Q: Key diagnostic test for RP?
A: Electroretinography
Explanation: Shows reduced rod response.
Q: RP + ataxia + ichthyosis?
A: Refsum disease
Explanation: Due to phytanic acid accumulation.
MCQs to test yourself
1.
A patient presents with night blindness and progressive peripheral vision loss. Fundoscopy shows pigment clumping in the retina. What is the most likely diagnosis?
A. Stargardt disease
B. Retinitis pigmentosa
C. Wet macular degeneration
D. Central serous retinopathy
Answer: B
Explanation: Classic triad + night blindness → RP.
2.
Which structure is first affected in retinitis pigmentosa?
A. Cones
B. Bipolar cells
C. Rods
D. Ganglion cells
Answer: C
Explanation: Rod degeneration → early nyctalopia.
3.
Which of the following is NOT a feature of retinitis pigmentosa?
A. Tunnel vision
B. Bone spicule pigmentation
C. Central vision loss early
D. Night blindness
Answer: C
Explanation: Central vision is preserved until late.
4.
A patient with RP also has hearing loss. What is the diagnosis?
A. Bardet-Biedl syndrome
B. Usher syndrome
C. Refsum disease
D. Kearns-Sayre syndrome
Answer: B
Explanation: RP + SNHL = Usher.
5.
Electroretinography in RP shows:
A. Increased cone response
B. Reduced rod response
C. Normal findings
D. Increased ganglion activity
Answer: B
Explanation: Rods affected first.
6.
Which gene therapy is used in RP with RPE65 mutation?
A. Ranibizumab
B. Voretigene neparvovec
C. Bevacizumab
D. Aflibercept
Answer: B
Explanation: First approved gene therapy for retinal dystrophy.
7.
Which of the following is false regarding RP?
A. It is inherited
B. It primarily affects peripheral retina
C. It causes early central vision loss
D. It leads to bone spicule pigmentation
Answer: C
Explanation: Central vision loss occurs late.
8.
Which condition is associated with phytanic acid accumulation and RP?
A. Usher syndrome
B. Refsum disease
C. Bardet-Biedl syndrome
D. Alport syndrome
Answer: B
Explanation: Refsum disease = lipid metabolism disorder.
Summary for quick exam revision
Retinitis pigmentosa is an inherited retinal dystrophy starting with rod degeneration causing night blindness and progressive peripheral field loss (tunnel vision), with the classic fundoscopic hallmark of bone spicule pigmentation in the peripheral retina along with vessel attenuation and optic disc pallor; it is associated with syndromes like Usher and Refsum disease, diagnosed by electroretinography, and managed mainly supportively with emerging gene therapy options.