Tonometry

Normal range — roughly 10–21 mmHg, with diurnal variation of a few mmHg; highest typically in the morning. Record the TIME with every reading, plus the method and each eye ("Ta 16/18 @ 2:15 pm"). Note when glaucoma patients last took their drops — a treated 16 and a missed-dose 16 mean different things.

IOP is a risk factor, not a verdict — ocular hypertension (high pressure, healthy nerve) and normal-tension glaucoma both exist. Asymmetry of more than 2–3 mmHg between eyes is worth flagging even when both are 'normal.' The number goes to the physician — never to the patient as a diagnosis.

Central corneal thickness — thick corneas over-read, thin corneas under-read; pachymetry contextualizes every pressure.

GAT is the reference standard: anesthetic + fluorescein (combination drop or moistened strip), cobalt blue light, ×10 on the drum.

Setup — forehead firmly on the band, chin on the rest, straight-ahead gaze. Loosen tight collars; coach normal breathing (Valsalva and breath-holding raise pressure). If lids need help, brace fingers on the orbital bone — never press the globe. Contact lenses come out first.

The touch — probe meets central cornea only; no lids, no lashes.

The endpoint — turn the drum until the INNER edges of the two fluorescein semicircles just touch. Overlapping mires = too much force; separated mires = too little.

Mire troubleshooting — thick, wide mires (too much fluorescein) over-read; thin, faint mires under-read; ragged mires in dry eye need fresh blinks and a prompt re-measure; oval mires in high astigmatism (~3 D+) need the biprism rotated per its markings or two readings 90° apart, averaged.

Repeats — rapid-fire repeated applanation massages aqueous out and drifts the reading down. Take one good measurement.

Safety — defer contact tonometry and ask the physician when there's a suspected open globe, fresh abrasion, or surface infection. Warn patients not to rub the numb eye for 15–20 minutes.

Non-contact (air puff) — nothing touches the eye, no drops; ideal for screening; confirm meaningful readings by applanation.

Rebound (iCare) — a tiny bouncing probe, no anesthetic; the pediatric and home-monitoring workhorse.

Tono-Pen — small-tip electronic applanation (with anesthetic); averages several readings with a confidence percentage; the tool for scarred and irregular corneas that ruin Goldmann mires.

Schiotz — weighted-plunger indentation on a supine patient; historic, but still an exam answer.

Disinfection is the non-negotiable — tonometer tips touch tears, the classic vector for epidemic keratoconjunctivitis. Reusable Goldmann tips get a timed disinfectant soak, rinse, and dry per CDC/manufacturer protocol — or the clinic uses disposable tips. A dry wipe disinfects nothing.