Conflicting Intraocular Pressure Readings at a Glaucoma Follow-up
Mrs. Delgado, 58, returns for a 6-month glaucoma follow-up. She uses latanoprost nightly and reports no visual complaints. The workup order is noncontact tonometry, then Goldmann applanation by the technician, then physician examination. Noncontact tonometry reads 29 mmHg OD and 27 mmHg OS; a repeat reads 30 mmHg and 26 mmHg. During the first attempt she held her breath, and her shirt collar was tight. Goldmann applanation with a calibrated tonometer, 0.5% proparacaine, and fluorescein strips reads 18 mmHg OD and 17 mmHg OS. The mires are slightly thick and overlapping. Central corneal thickness is 545 µm OD and 550 µm OS. Her previous Goldmann readings over 3 years have ranged from 16 to 19 mmHg. The physician is running 45 minutes behind, and the room is busy. The technician must decide which pressure to report and whether any additional checks are needed before the patient is dilated.
1. Which IOP values should the technician treat as most credible, and what factors explain the discrepancy?
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Goldmann applanation is the more credible measurement here, but it is not automatically 'correct.' The noncontact readings of 26–30 mmHg conflict with three years of Goldmann values in the 16–19 mmHg range and with a cornea that appears normal. Noncontact tonometry is sensitive to breath-holding and Valsalva, which raise IOP, as well as a tight collar, blinking, poor fixation, and an irregular tear film. The first reading was taken during a breath-hold, so the 29–30 mmHg values are suspect.
Goldmann can also be falsely high when the fluorescein mires are thick or overlapping, as noted here, so the 18/17 mmHg may be slightly high rather than low. Central corneal thickness of 545–550 µm is near average and does not explain a large discrepancy. The correct approach is not to average the two instruments or report the higher number. Repeat the Goldmann after improving technique, then report both sets of readings with the conditions documented.
2. What specific steps should the technician take to verify the Goldmann reading before recording it?
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First confirm that the tonometer is calibrated and the prism is clean; a dirty or damaged prism distorts the mires. Check corneal anesthesia and dry the inferior cul-de-sac if tears are pooling, then apply a controlled amount of fluorescein so the mires are thin and barely touching. Have the patient sit back, loosen the collar, breathe normally, and look at a distance target with the eyes wide but not squeezed. Retract the lids against the orbital rim and never press on the globe. Center the mires, take at least two readings, and repeat if they differ by more than 2–3 mmHg. Inspect for corneal edema or epithelial disruption. Compare with the fellow eye and prior readings. If the repeat remains in the high teens, record it; if it rises toward the noncontact values, escalate to the physician rather than dismissing it.
3. What should be documented and communicated to the physician, and what should not be said to the patient?
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Document both noncontact and Goldmann values, the time, patient position, breath-holding and collar issues, mire quality, tonometer calibration status, corneal thickness, and the prior range. Note that noncontact tonometry was repeated and that Goldmann was repeated after technique adjustment. Flag the discrepancy clearly for the physician rather than resolving it silently.
Tell the patient only that you are repeating the pressure check and that the doctor will review the results. Do not say she has glaucoma, that her drops are failing, or that one machine is 'wrong.' Do not change or advise stopping medication. If the physician is delayed, keep the record available and give a verbal handoff so the discrepancy is not lost.