General Medical Information

Intraocular Pressure

Jean Edwards Holt

Measurement of intraocular pressure (IOP) should be a part of every general physical examination. The examiner can estimate IOP digitally by placing the tips of the index fingers on the patient’s closed eyelids. All but gross abnormalities remain undetected when this technique is used. Tonometry is estimation of IOP with an instrument. It can be performed with an indentation technique or an applanation technique. The former is used in the general screening process and performed with a Schiotz tonometer. With the patient in a recumbent position, a drop of topical anesthetic is instilled into each eye. The patient is instructed to look straight ahead with both eyes open. Assistance in holding the eyelids open, with pressure on the orbital bones only, may be needed. The plunger is gently placed on the center of the patient’s cornea, and the corresponding scale reading is recorded. The test should require only 1 to 2 seconds of contact with the cornea. Normal IOP usually is 15 ± 3 mm Hg, with an upper limit of 22 to 23 mm Hg.