Examination methods and diagnostics in ophthalmology
Diagnostics is the domain where examiners test sequence and interpretation rather than device names. You must know what each test measures, its reliability indices, and when a result changes management.
Vision and the front of the eye
Snellen acuity is not linear; logMAR with ETDRS letters is. A pinhole improves refractive blur but not media opacity or retinal disease. Contrast sensitivity detects subtle disease when acuity is 1.0. Amsler grid for metamorphopsia; Ishihara for red-green defects; D-15 for acquired dyschromatopsia. Pupil examination includes size, direct and consensual response, and the swinging flashlight test for a relative afferent pupillary defect.
Pressure, angle and cornea
Goldmann applanation is the reference; it reads low in thin corneas and after myopic laser surgery and high in thick corneas, so pachymetry matters. Tonopen or iCare for irregular surfaces. Gonioscopy with a mirrored lens in dim light without pressure, with indentation if the angle appears closed; grade with Shaffer. Disc assessment covers cupping, rim, haemorrhages, and OCT retinal nerve fibre layer.
Fields and imaging
Humphrey 24-2 or 30-2 for glaucoma, 10-2 for advanced or macular disease; watch fixation losses, false positives and false negatives. Pattern deviation removes cataract-induced general depression and the glaucoma hemifield test flags asymmetry. OCT quantifies macular oedema and nerve fibre layer thickness; OCT angiography shows capillary loss without dye. Fluorescein angiography phases run choroidal, arterial, arteriovenous, venous and late leakage. B-scan for opaque media; ultrasound biomicroscopy for the ciliary body and angle.
Worked example
A 62-year-old with cup-to-disc 0.8 and pressure 26 mmHg. Reasoning: you need a baseline field and OCT nerve fibre layer, gonioscopy to exclude a narrow angle, and pachymetry to know whether the pressure reading is trustworthy; the diagnosis rests on structure plus function, not pressure alone.
Traps
Accepting a field with high fixation losses; diagnosing glaucoma from cupping alone; omitting the fellow disc; using a pinhole to exclude macular disease.