A Frog Just Got an Eye Pressure Test The eye pressure test that uses a tiny probe with a white plastic tip is called rebound tonometry. It works on a simple principle: the way an object rebounds after a quick contact depends on the stiffness of what it touches. In this test, the probe gently taps the cornea for just a split second, then bounces back. The machine measures both the speed and distance of that rebound. If the intraocular pressure (IOP) is high, the cornea resists indentation and pus