Intraocular Pressure and Glaucoma Assessment
Goldmann applanation
Anesthetize with proparacaine, stain with sodium fluorescein, and align the mires so their inner edges just touch, the standard endpoint. Calibrate the tonometer and record the time and instrument used. Normal is roughly 10 to 21 mmHg, but the number is not a diagnosis: central corneal thickness, curvature, and astigmatism all bias the reading. Thin corneas underestimate and thick corneas overestimate pressure, so pachymetry is needed to interpret the value.
Alternatives and angle assessment
Tonopen, iCare rebound, Perkins, and Schiotz are acceptable alternatives with different sources of error. Gonioscopy is the only way to assess the angle: identify Schwalbe's line, trabecular meshwork, scleral spur, ciliary body band, and grade with the Shaffer system (IV open through I closed). Indentation gonioscopy distinguishes appositional from synechial closure.
Worked example
Pressure is 26 mmHg in a cornea measuring 490 micrometers. Because a thin cornea underestimates true pressure, the corrected value is higher, perhaps 29 to 30 mmHg, making the case more concerning rather than less. Repeat the measurement, examine the angle, and image the disc.
Traps
Not calibrating, or not confirming the 1 to 2 mm mire endpoint. Pressing on the globe during measurement. Using anesthetic without fluorescein. Treating a single reading as a diagnosis. Failing to document which instrument was used.