Tonometer Calibration Drift and a Cluster of Asymmetric IOPs
Over six weeks, a three-lane practice notices that 12 patients examined in lane 2 had Goldmann applanation IOP readings 4–6 mmHg higher than readings taken in lanes 1 or 3 on the same day. One patient, a 61-year-old woman with a family history of glaucoma, was started on latanoprost after a single lane-2 reading of 26 mmHg in each eye; a repeat in lane 1 two weeks later was 18 mmHg OU. The tonometer in lane 2 was last calibrated 14 months ago; practice policy says every 6 months. The calibration log has two blank entries. Staff say the lane-2 tonometer "has always been a little high" and that they adjust mentally. No patient has complained. The practice owner is on vacation; the office manager wants to wait until next month to review.
1. What immediate patient-safety actions should you take, and why can this not wait for the owner's return?
Read the worked answer
Immediate patient safety comes before the owner's vacation. I would take the lane-2 tonometer out of service, tag it, and verify calibration with the standard weight or send it for service. I would pull the records of the 12 patients and recheck IOP with a calibrated tonometer, prioritizing anyone whose management changed-especially the woman started on latanoprost. For her, I would arrange an urgent recheck, review the optic nerve and visual field, and discuss whether the original 26 mmHg was artifact. I would not tell her to stop the drop by phone without an examination, but I would make clear that a medication may have been started on a faulty reading. I would notify the medical director and risk manager the same day, start an incident report, and document the actions. The office manager's 'next month' plan is not acceptable because additional patients could be misclassified.
2. Conduct a root-cause analysis: what system failures allowed this to happen, and what fixes would you put in place?
Read the worked answer
The root cause is not 'one bad tonometer.' The calibration interval was exceeded, the log had blanks, and staff had normalized a workaround-mentally adjusting readings-which is unsafe. A just-culture review should ask why calibration was not owned, whether reminders existed, whether the practice had a second-person check, and whether staff felt safe raising the discrepancy. System fixes: assign a named calibration owner, set automatic reminders every 6 months plus a monthly verification check, require a log signature, remove any tonometer that fails, and train staff that 'adjusting mentally' is prohibited. I would audit IOP readings across lanes for several weeks and review all treatment decisions made from lane-2 readings. I would also check whether the same issue affects other equipment, such as the perimeter or autorefractor. The goal is a reliable process, not a single apology.
3. How would you disclose this to the patient who was started on latanoprost?
Read the worked answer
Disclosure should be prompt, specific, and non-defensive. I would speak with the patient privately, explain that a calibration problem was found, that her initial reading may have been falsely high, and that we are rechecking before deciding whether she needs the drop. I would apologize for the uncertainty and the extra visit, without speculating beyond the facts. I would arrange the recheck at no charge if practice policy allows, review the optic nerve and visual field, and document the conversation. If the repeat IOP is normal and there is no glaucomatous damage, I would discuss stopping the prostaglandin with the prescribing clinician and monitor. I would also explain what the practice is doing to prevent recurrence. The incident report and the medical record should be accurate but not blame an individual in the clinical note. The patient's trust depends on candor and a clear plan.