A 19-year-old patient was referred to the medical retina clinic. He had experienced difficulty with vision at night and hearing for as long as his mum could remember. More recently, he had increasing difficulty looking at objects in the periphery, beginning to bump into things inadvertently. The hearing loss itself was non-progressive.
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1. What are the two main ophthalmic causes of tunnel vision?
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Correct answer: Both very advanced glaucoma and retinitis pigmentosa (RP) can cause tunnel vision. The age and hypoacusis of our patient suggest the diagnosis is likely to be an RP-associated disease.
The most common cause of both deafness and blindness is Usher syndrome. Usher syndrome has three subtypes, each with variability in visual and hearing symptoms. The hearing loss is due to damage to the cochlea nerve cells.
The original definition of pre-eclampsia included non-dependent edema (ie, swelling of the hands and face), but this is no longer a prerequisite for the diagnosis.
The diagnosis of pre-eclampsia should be made only after 20 weeks’ gestation. Evidence of gestational proteinuric hypertension before 20 weeks’ gestation should raise the possibility of an underlying molar pregnancy, drug withdrawal, antiphospholipid antibody syndrome, or (rarely) a chromosomal abnormality in the fetus.
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2. What are the clinical features of retinitis pigmentosa (RP) on ophthalmoscopy?
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Correct answer:
The most common clinical signs on dilated fundoscopy include:
- Bone speculated pigmentation
- Waxy pallor of the optic disc
- Attenuation of the retinal vessels.
The following ophthalmic manifestations can also be seen:
- Optic nerve drusen (sometimes mistaken as swollen disc)
- Keratoconus
- Epiretinal membrane
- Cystoid macular oedema
- Posterior sub-capsular cataract.
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3. In which cells does the pathology reside?
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Correct answer:
The presenting features of RP are partly determined by which cell types are affected by RP. The following cells can be affected:
- Cones
- Defective central vision.
- Rods
- Difficulty in night vision (nyctalopia).
- Retinal pigment epithelium.
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4. What is the inheritance pattern?
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Correct answer:
RP is the most common inherited retinal degeneration, and over 100 genes can be affected. The condition is inherited in autosomal dominant, recessive and X-linked fashion.
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5. Why is Refsum’s disease an important RP-associated disorder to identify?
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Correct answer:
Patients with Refsum’s disease have a deficiency in phytanic oxidase, leading to a build-up of phytanic acid. Hence, Refsum’s disease is a storage disorder and subsequently exhibits neurological manifestations, such as cerebellar degeneration and peripheral neuropathy. This is the most important RP-associated disorder as one can attempt to minimise the build-up of phytanic acid by implementing a restricted diet.
