The cornea is the clear window that makes up the front of the eye. It has a normal thickness of 540 microns and this can be measured in the office with a handheld device called a pachymeter (see pachymetry). Corneal thickness is important for a couple of reasons. When we check eye pressure using applanation tonometry (the blue light on the slit lamp microscope) we press on the eye to measure how “hard” the cornea “feels.” A thick cornea can give a falsely high pressure reading while a thin cornea can give a falsely low pressure. Thin corneas have been found to be an independent risk factor for glaucoma. Also, if you are contemplating LASIK surgery, you need to have a thick enough cornea to be a good candidate.