Neuro-ophthalmology
Neuro-ophthalmology tests whether you can localise a lesion from a pupil, a field and a fundus. Classic questions involve optic neuritis, ischaemic optic neuropathy, papilloedema, pupil abnormalities and ocular motor palsies.
Core rules
- Relative afferent pupillary defect: use the swinging flashlight test; a positive RAPD indicates asymmetric optic nerve or extensive retinal disease. It is absent in bilateral symmetric disease.
- Optic neuritis: unilateral painful subacute visual loss, dyschromatopsia, RAPD, a swollen disc in a third, and a normal or swollen nerve on imaging. Multiple sclerosis risk is stratified by MRI lesions; intravenous methylprednisolone speeds recovery but does not change final acuity.
- Non-arteritic anterior ischaemic optic neuropathy: sudden painless altitudinal field loss, sectoral disc oedema, a small cup, age over 50. There is no proven treatment; manage vascular risk factors.
- Giant cell arteritis: age over 50, headache, jaw claudication, scalp tenderness, raised ESR and CRP. Give intravenous or high-dose oral steroid immediately and arrange temporal artery biopsy within two weeks.
- Papilloedema: bilateral disc swelling with preserved acuity and an enlarged blind spot; investigate with neuroimaging and lumbar puncture.
- Third nerve palsy: pupil involvement suggests compression, classically a posterior communicating artery aneurysm; pupil-sparing palsy is more often microvascular. Fourth nerve palsy causes vertical diplopia worse on reading; sixth nerve palsy causes horizontal diplopia.
Worked example
A 62-year-old man has sudden drooping of the right lid, a dilated right pupil and an eye that is down and out. Because the pupil is involved, this is a compressive third nerve palsy until proved otherwise. You arrange urgent CT or MR angiography for a posterior communicating artery aneurysm; you do not wait for a microvascular recovery trial, which would be appropriate only for a pupil-sparing palsy in a diabetic patient.
Traps
Attributing a pupil-involving third nerve palsy to diabetes, missing giant cell arteritis in an elderly patient with a swollen disc, and diagnosing papilloedema without checking blood pressure and medications.