Optometric Examination and Diagnostic Procedures
This domain tests technique, calibration, and interpretation: whether you know what a test actually measures, when it is unreliable, and how to combine results into a coherent assessment.
Technique determines the number
- Goldmann applanation tonometry requires fluorescein, correct mire alignment, and a calibrated instrument. Intraocular pressure is underestimated in thin corneas and overestimated in thick ones; central corneal thickness modifies interpretation, not the measurement itself.
- Non-contact tonometry is sensitive to patient cooperation and is a screening tool rather than a substitute for applanation when the pressure is borderline.
- Gonioscopy with indentation distinguishes appositional from synechial angle closure; a slit-lamp estimate of angle depth is not gonioscopy.
Interpreting tests in context
Visual field reliability indices matter: high fixation losses, false positives, or false negatives weaken the result. A single field is never diagnostic; glaucomatous change requires a repeatable pattern with structural correlation on optic nerve or retinal nerve fibre layer imaging.
Worked example
A patient has Goldmann pressure of 19 mmHg in each eye, central corneal thickness of 490 micrometres, and a suspicious neuroretinal rim. Reasoning: the measured pressure likely underestimates the true pressure because thin corneas bias applanation readings downward. The correct action is to repeat tonometry, examine the angle, obtain baseline fields and nerve imaging, and set a closer review, not to record "normal pressure" and discharge.
Traps that cost marks
- Treating one pressure reading or one visual field as a diagnosis.
- Forgetting calibration status when equipment results conflict with clinical impression.
- Performing gonioscopy without indentation and missing a closed angle.
- Comparing a patient's retinal nerve fibre layer to a normative database without checking signal quality and disc size.