4.2 Tonometer Disinfection, Calibration & Post-Procedure IOP Monitoring

Tonometer Disinfection, Calibration & Post-Procedure IOP Monitoring

Reusable applanation prisms contact tears and the corneal surface. They can transfer adenovirus, herpes viruses, bacteria, fungi, or other material if the workflow is incomplete. Cleaning, disinfection, rinsing, drying, storage, and calibration are distinct steps.

Cleaning and disinfection

After use, move the prism into the designated dirty area without touching clean supplies. Inspect it for cracks, chips, crazing, or surface damage. Remove visible mucus and fluorescein using the cleaning method allowed by the manufacturer. Organic material can reduce disinfectant action.

CDC guidance for reusable tonometer tips includes immersion for 5 to 10 minutes in either 5,000 ppm available chlorine or 70% ethyl alcohol, followed by thorough rinsing and air drying. However, chemical compatibility matters: repeated exposure to a chemical not approved in the device instructions can damage a prism and create a patient-safety problem. Follow the current manufacturer instructions and facility infection-control policy. If the approved device process differs or a disposable tip is used, follow that validated workflow.

Do not equate “alcohol” products. CDC notes that 70% isopropyl alcohol is not effective against adenovirus for tonometer disinfection. A quick surface wipe also lacks the required contact time. Household bleach concentrations vary, so prepare a chlorine solution by measured concentration under policy rather than memorizing a universal household dilution. Label the solution, observe its specified usable life, and never mix chlorine with ammonia or acids.

Rinse as directed to prevent chemical keratitis, allow the prism to dry, inspect it again, and store it in a protected clean area. Hand hygiene and clean gloves prevent recontamination.

Model-specific calibration

Calibration verification checks the instrument; it does not repair it. Use the instructions for the exact model and serial configuration. The Haag-Streit AT 900 instructions call for a monthly check and after suspected damage. With its test weight, verify the measuring-drum positions 0, 2, and 6.

For that model, the allowable drum ranges are:

• position 0: −0.05 to +0.05;
• position 2: 1.95 to 2.05;
• position 6: 5.9 to 6.1.

Because the clinical scale is read by multiplying the drum value by ten, the permitted error is not identical at every point: the position-6 band is wider than at position 2. Do not generalize one ±0.5 mmHg claim to all three checks or to another manufacturer.

Perform the check exactly as the instructions describe, without forcing the feeler arm. Record date, device identifier, test points, results, initials, and action. If the unit fails, label and remove it from clinical use and route it for authorized service. Do not compensate by mentally adding a correction to patient readings.

Post-procedure pressure and perfusion checks

An intravitreal injection can cause a transient IOP rise. The clinic's protocol may call for gross vision, symptoms, optic-nerve or retinal-artery perfusion assessment, and tonometry. Confirm the ordered method and avoid touching a fresh injection site.

Immediately alert the physician for no-light-perception vision, severe pain, nausea with a firm eye, corneal edema, marked pressure elevation, or absent retinal-artery perfusion. The clinician determines whether observation, pressure-lowering medication, anterior-chamber paracentesis, or another intervention is indicated. A technician should not independently perform an invasive treatment.

Steroid exposure can cause delayed ocular hypertension, so document the agent, date, IOP method, and trend. Gas or silicone oil may also affect pressure. A measurement is only useful when the prism is clean, the device passes calibration, technique is sound, and the result is routed appropriately.

Reading the result in context

A pressure value is not self-interpreting. Record the device, eye, time, topical anesthetic or dye when applicable, patient position, repeated values, and factors that may affect technique. Lid squeezing, breath-holding, Valsalva, corneal edema, scar, irregular astigmatism, contact lenses, recent surgery, and poor centration can alter a reading. Do not apply a universal numerical correction for corneal thickness.

When readings are unexpected, check eye identity, instrument status, tip or cover, alignment, and patient behavior. Repeat only within protocol, compare with another approved method when ordered, and route the result. The licensed clinician decides whether the value represents glaucoma, a post-procedure spike, artifact, or another condition.

Documentation after cleaning or a failed check

Record the device or prism identifier, product and concentration, contact time, rinse and drying steps when required, operator, date, and any integrity concern. If a calibration check is outside the manufacturer's tolerance, label the instrument out of service, prevent patient use, and follow the service pathway. Do not compensate for drift by mentally adjusting patient readings. After repair or replacement, complete the required function check before clinical return.