4.1 Goldmann Applanation & Handheld Tonometry Techniques

Applanation and Handheld Tonometry

Intraocular pressure is an estimate influenced by the instrument, cornea, patient behavior, position, and technique. It supports clinical assessment but does not independently diagnose glaucoma, hypotony, perfusion failure, or a post-procedure complication.

Pre-measurement controls

Verify patient and eye, order, device identity, calibration or self-test status, clean or single-use patient-contact component, and contraindications under protocol. Explain that the patient should breathe normally, keep both eyes open, and avoid squeezing. Remove a contact lens when the method requires it. Record recent ocular surgery, trauma, corneal disease, severe pain, or infection concern and ask the clinician before contacting an unsafe surface.

The patient's head and gaze should be stable without tight collars, breath holding, Valsalva, lid pressure, or examiner fingers on the globe. Measure in the ordered position; sitting and supine results are not automatically interchangeable.

Goldmann applanation

Goldmann applanation uses a modified Imbert-Fick relationship. At a nominal 3.06 mm applanated diameter, tear-film attraction and corneal resistance are treated as approximately balancing for the instrument design. Real corneas vary, so the result is an estimate rather than a direct pressure gauge.

Use topical anesthetic and fluorescein only under the authorized method. Seat the disinfected prism correctly, begin with low force, center it on the cornea, and bring the two fluorescein semicircles into equal focus. Adjust until the inner borders meet at the instrument-defined midpoint of pulsation. Withdraw without scraping the cornea, inspect the patient as required, and prevent the used prism from contaminating clean surfaces.

Too much fluorescein or tearing can create broad mires and bias the reading; too little dye or poor illumination can make the endpoint difficult. Decentration, unequal mire size, corneal scar or edema, high astigmatism, examiner pressure on the lids, and patient squeezing also affect results. Use the model's astigmatism method and document corneal or technical limitations rather than applying a homemade correction.

Central corneal thickness and biomechanical properties can influence applanation, but a technician should not simply add or subtract a fixed number of mmHg. The clinician interprets pressure with pachymetry, optic nerve, angle, history, and other findings.

Handheld and noncontact methods

Handheld applanation devices, including Tono-Pen models, use a small contact area and multiple samples. Install the specified single-use cover, perform the model's calibration or startup check, hold the probe as directed, and accept or repeat from the displayed confidence or variability guidance. Do not use a universal quality cutoff across models.

Rebound tonometers, including iCare models, propel a lightweight single-use probe and measure its motion after brief corneal contact. Topical anesthetic is typically not required for models and uses specified by the manufacturer. Correct distance, probe alignment, patient position, disposable handling, and the model's quality display matter.

Noncontact tonometry estimates pressure from corneal deformation during an air pulse. It avoids direct corneal contact but still requires clean equipment, correct alignment, and infection-control attention to nearby surfaces and tear contamination. Blinking, anxiety, fixation loss, irregular cornea, and high or low pressure ranges can reduce reliability.

No alternative is universally interchangeable with Goldmann. A change in method can produce a change in result, so record the device and position and compare trends cautiously.

Unexpected or post-procedure readings

For an implausible value, verify eye, unit, probe or prism, calibration status, alignment, patient behavior, and display quality. Repeat only as permitted, or compare with another ordered method. Preserve both results and the reason for repetition.

Severe pain, nausea, corneal edema, a fixed pupil, sudden vision loss, profound hypotony, or absent retinal perfusion after a procedure is not a routine “recheck later” finding. Notify the clinician immediately and activate the clinic's emergency pathway. The licensed practitioner determines examination and treatment.

Documentation for longitudinal comparison

Record right and left readings separately, device and model when relevant, patient position, time, repeat values, and any factor that limits comparison. Note squeezing, poor fixation, corneal scar or edema, contact-lens issue, recent surgery, or use of a different method. If multiple readings are obtained, follow the protocol for reporting rather than selecting the most reassuring value. A meaningful trend uses comparable technique, but an urgent symptomatic value is escalated even when the prior method was different. Never hide a failed attempt or copy a previous pressure into the current visit. Clear records make later change safer to interpret.

Before accepting a pressure reading

• confirm the patient, eye, device, ordered method, and required infection-control preparation;
• position the patient and instrument without pressing on the globe or eyelids;
• inspect the measurement quality indicators and repeat only under the device and clinic protocol;
• record the value, time, eye, instrument, relevant difficulty, and any authorized repeat; and
• promptly route unexpected, asymmetric, or symptom-associated findings without independently diagnosing or changing treatment.