A tonometer is a tool used to measure the pressure inside the eye to examine the health of the eyes and the optic nerve. One type of tonometer directly touches the eyeball, another only touches the eyelid, and the "air puff" tonometer makes no contact with the eye at all, but instead directs a small puff of air at the cornea before measuring the force needed to flatten it. The air puff device does not usually require the use of eye drops, and results are delivered almost immediately.