Tonometry for the COA®: Goldmann Applanation Step by Step

Tonometry is 7% of IJCAHPO’s COA® content areas effective 8/1/2025. Goldmann applanation follows a set order: numb and stain the eye per clinic protocol, view under cobalt blue light, turn the dial until the semicircles’ inner borders meet, then multiply the dial reading by 10 to get mmHg. Clinic protocol governs.

Last checked Nov 2, 2026. Confirm fees and dates with the certifying body. optical.education is independent and is not affiliated with or endorsed by IJCAHPO. Disclaimer.

This is exam study material, not clinical training. Follow your clinic’s protocol and your supervising doctor.

Why it’s on the COA

Tonometry is 7% of the COA content areas effective 8/1/2025 (checked Nov 2, 2026).

Before you start

• Drops: applanation touches the cornea, so the eye gets a topical anesthetic plus fluorescein dye, given the way your clinic’s protocol says.
• Light: cobalt blue filter in, slit open and brightness turned all the way up, with the light coming in from the side at roughly 60°.
• Patient: seated at the slit lamp with the chin resting in its cup and the forehead pressed to the bar above, eyes straight ahead.

The end point

Once the tip is on the cornea you see two green semicircles. Adjust the dial until their inner borders meet. Mire thickness, alignment and what affects the reading are covered on the applanation tonometer simulator page; practice there until the end point is automatic.

Reading and recording

The dial number × 10 is the pressure in mmHg (2.1 → 21 mmHg). Record it in mmHg for the eye you measured.

Infection control

Clean and disinfect the tip exactly as the manufacturer’s instructions and your clinic’s infection-control protocol say.

Practice questions

1. The dial reads 1.8 when the mires line up. What is the pressure?

   Show answer

   1.8 × 10 = 18 mmHg

2. What light is used to see the fluorescein mires?

   Show answer

   Cobalt blue

3. At the end point, which parts of the two semicircles meet?

   Show answer

   Their inner borders.