This is how we measure the pressure inside the eye. The internal eye pressure is extremely important for the health of the eye. If the pressure is too high, glaucoma damage will occur. If too low, the eye deflates like a water balloon and retinal distortions and macular edema can occur. There are many ways to check the eye pressure, such as the “air puff test,” but the one used most often is called the Goldman Applanation Tonometry. This is a small plastic probe that is illuminated with a blue light. As the probe pushes on the eye it flattens a small area of the cornea. The amount of pressure required to flatten the cornea can be used to estimate the internal ocular pressure. This is a relatively accurate device, though corneal thickness can make the readings less so. This applanation tonometry is generally less aggravating then the air puff test. Another tonometry device is called the Tono-Pen. This is a handheld machine that looks like a pen. It is touched to the surface of the eye and works by a similar method. The Tono-Pen is not as accurate as other methods, but is sometimes the only way to accurately measure pressure in a person who is bedridden or who can’t get their head into a microscope.