This test detects problems with pressure in the eye. Increased pressure is a sign of glaucoma. Your provider places drops in your eyes to numb the area. Then an instrument called a tonometer blows a small puff of air on the cornea. During applanation tonometry, your provider uses a flat-tipped cone that gently comes into contact with your cornea. The device measures the amount of pressure needed to flatten a portion of your cornea.