Normal eye pressure is between 12 and 22 millimeters of mercury, state the Glaucoma Research Foundation. The method of measuring eye pressure is called tonometry and is done with a device called a tonometer.
Tonometry involves numbing the eyeball with anesthetic drops and then using the tonometer device to lightly push on the cornea, according to MedicineNet. The device measures the resistance to this pressure.
Eye pressure higher than 22 mmHg is considered ocular hypertension, states the Glaucoma Research Foundation. This is not the same as glaucoma, but it is a risk factor for developing glaucoma. High intraocular pressure can damage the optic nerve and cause blindness over time.