Neuro-ophthalmology
This section covers neuro-ophthalmology: pupillary abnormalities, optic nerve disease, visual field defects, and ocular motor palsies. The exam tests localisation and emergency recognition.
Core rules and concepts
- A relative afferent pupillary defect indicates asymmetric optic nerve or severe retinal disease; it is tested with the swinging flashlight test.
- Optic neuritis causes painful subacute vision loss, reduced colour vision, and a RAPD; MRI brain and orbits assesses demyelination risk.
- Papilloedema is bilateral disc swelling from raised intracranial pressure; it usually preserves central vision until late.
- A third-nerve palsy with pupil involvement suggests compression, such as posterior communicating artery aneurysm, and needs urgent imaging.
- Horner syndrome causes ptosis, miosis, and anhidrosis; localisation uses cocaine or apraclonidine testing and imaging of the sympathetic pathway.
Worked example
A 30-year-old woman has two days of pain on eye movement and blurred vision in the right eye. Visual acuity is 20/60, colour vision is reduced, and there is a right RAPD. The fundus is normal. The diagnosis is retrobulbar optic neuritis. MRI shows a demyelinating lesion. Intravenous methylprednisolone may speed recovery but does not change final acuity; it is considered when vision is severely affected. She is referred for neurological assessment because white matter lesions increase the risk of multiple sclerosis.
Traps that cost marks
A pupil-involving third-nerve palsy is an aneurysm until proven otherwise; do not arrange routine review. Checking visual acuity alone misses a RAPD. Bilateral disc swelling is not papilloedema until intracranial pressure is assessed. Do not label all optic disc swelling as optic neuritis; consider ischaemic, compressive, and toxic causes.