6.2 Core Workflows and Decision Points

6.2 Core Workflows and Decision Points

The COA exam expects you to perform Goldmann applanation tonometry (GAT) in the correct order and to recognize the proper endpoint. Memorize the sequence as a fixed workflow.

The Goldmann applanation sequence

1. Verify the prism and calibration. Use a disinfected GAT tip set so the white line on the prism aligns with the white 0 marker on the holder (set to 0 unless astigmatism >3 D requires aligning the red mark to the flat axis).
2. Instill anesthetic and dye. Apply a topical anesthetic combined with fluorescein. Proparacaine 0.5% with fluorescein (Fluress) is the standard; it anesthetizes the cornea within ~15 seconds and supplies the dye needed to see the mires.
3. Seat the patient. Chin in the rest, forehead against the band, fixating straight ahead. Ask the patient to open both eyes wide and breathe normally; holding the breath or squeezing the lids falsely raises IOP.
4. Set illumination. Swing the cobalt-blue filter into the beam, open the slit fully, and angle the light ~60 degrees to the prism.
5. Advance the prism until it just touches the cornea; two glowing fluorescein semicircles (mires) appear.
6. Find the endpoint. Turn the force dial until the inner edges of the two semicircles just touch (forming an S or figure-of-eight). Read the dial.
7. Convert. Multiply the dial reading by 10. A dial of 1.6 = 16 mmHg.

Reading the mires correctly

A pulsation amplitude of roughly 0.25 mm of dial movement is normal arterial pulsation; read at the average.

Choosing an alternative device

GAT cannot always be used. Decision points the exam tests:

• Cannot sit at the slit lamp (bedridden, child, wheelchair) -> use the handheld Tono-Pen or Perkins.
• Irregular, scarred, edematous, or post-surgical cornea -> GAT is unreliable; the Tono-Pen samples a small area and tolerates irregularity better.
• Patient cannot tolerate contact or you need rapid screening -> non-contact air-puff tonometry, no anesthetic required.

How the handheld and non-contact devices work

The Tono-Pen is a battery-powered handheld applanation tonometer with a small strain-gauge tip covered by a disposable latex-free cover (Ocu-Film). The technician taps the tip lightly and repeatedly against the anesthetized cornea; the device averages several valid readings and displays the mean IOP along with a statistical reliability percentage. Because the sampling area is tiny, the Tono-Pen tolerates scarred, edematous, or irregular corneas far better than Goldmann and can be used with the patient lying down.

The Perkins is essentially a portable Goldmann that uses the same prism and fluorescein mires but is handheld and battery-illuminated, giving Goldmann-quality readings outside the slit lamp.

Non-contact (air-puff) tonometry directs a calibrated pulse of air at the cornea and times how long it takes to flatten a fixed area, converting that interval into mmHg. Its great advantage is that nothing touches the eye, so no anesthetic or dye is needed and cross-infection risk is minimal, which makes it ideal for screening, children, and anxious patients. Its weakness is lower precision and a tendency to read higher at the upper end of the range, so abnormal air-puff values are typically confirmed by Goldmann.

Documentation that wins the question

Record the device used, the time of day (for diurnal interpretation), and the value for each eye separately, written as OD (right) and OS (left), for example 'GAT 16 mmHg OD / 15 mmHg OS at 0930.' A bare number without the instrument and time is incomplete, because a 22 mmHg air-puff screening reading and a 22 mmHg morning Goldmann reading mean different things to the physician. The exam consistently favors the answer that produces an accurate value, names the instrument, notes the time, and keeps the cornea safe.

A clean reading documented with its instrument and time is the defensible choice, and it is also what a competent technician actually does at the chair.

Patient coaching that protects the reading

Half of a good measurement is patient handling. Before any contact device, explain that the patient will feel a light touch but no pain, that they should keep both eyes open and look straight at the target, and that they must breathe normally rather than holding their breath. Watch for the patient who anticipates the prism and pulls back or squeezes; a squeeze transmits orbicularis muscle force to the globe and inflates the reading. If you are holding the lids open, brace your fingers on the bony orbital rim, never on the globe itself, because finger pressure on the eye raises IOP directly.

Coaching also reduces the number of repeat applanations, which matters because repeatedly touching the cornea can massage aqueous out and progressively lower the apparent pressure, so you want the first reading to be the clean one. These habits convert a technically correct procedure into a clinically trustworthy number, and the exam rewards the choice that controls the patient before recording a surprising value.