Investigations
This section covers ophthalmic investigations: imaging, electrophysiology, visual fields, angiography, and tissue diagnosis. The exam tests indication and interpretation rather than machine detail.
Core rules and concepts
- OCT provides cross-sectional retinal and optic nerve imaging; it is used for macular oedema, epiretinal membrane, and glaucoma progression.
- Visual fields document functional loss; reliability indices and fixation losses must be checked before interpretation.
- Fluorescein angiography shows leakage, staining, and non-perfusion; ICG angiography is useful for choroidal disease.
- B-scan ultrasound assesses the posterior segment when the view is opaque and detects intraocular foreign bodies or tumours.
- Electrophysiology includes ERG for retinal function and VEP for optic nerve pathways; temporal artery biopsy is the gold standard for giant cell arteritis.
Worked example
A 72-year-old has sudden painless visual loss, a swollen optic disc, and a raised ESR. Giant cell arteritis is suspected. High-dose intravenous methylprednisolone is started immediately, before confirmation, to protect the fellow eye. Temporal artery biopsy is arranged within 1–2 weeks; a negative biopsy does not exclude the diagnosis if clinical suspicion is high. CRP and platelet count support the diagnosis. The biopsy shows granulomatous inflammation with giant cells.
Traps that cost marks
Ordering tests without a clinical question wastes resources and delays treatment. Do not wait for biopsy before steroids in suspected arteritic ischaemic optic neuropathy. A single normal OCT does not exclude glaucoma. In opaque media, ultrasound is safer than MRI when a metallic foreign body is possible.