Investigative Procedures and Diagnostic Imaging
What this domain tests
Investigations questions test when to order a test, how to interpret it and how to recognise artefacts. Structure-function correlation is a recurring theme.
Core tests
- Visual field: Humphrey 24-2 or 30-2; check fixation losses, false positives and false negatives before interpreting.
- OCT: macular thickness and RNFL; useful for AMD, diabetic maculopathy and glaucoma progression.
- Fundus photography and FFA for vascular disease; B-scan when media are opaque; A-scan for axial length.
- Topography and pachymetry for keratoconus and refractive planning; gonioscopy for angle assessment.
- Optical biometry measures axial length for IOL calculation and is preferred when media are clear.
Field patterns
- Arcuate defect: glaucoma.
- Bitemporal hemianopia: chiasmal lesion.
- Homonymous hemianopia: retrochiasmal lesion.
- Central scotoma: macular or optic nerve disease.
Worked example
A patient has a bitemporal field defect on repeated reliable testing. Reasoning: the defect respects the vertical midline and involves both temporal fields, localising to the optic chiasm. Request neuro-imaging and refer; do not attribute it to glaucoma.
Traps
Interpreting a field with high fixation losses; calling an artefact a defect; using A-scan when a B-scan is needed; failing to repeat an inconsistent test.