Accurate estimation of intraocular pressure is an essential aspect in the diagnosis and management of glaucomatous eye disease. Glaucoma is a progressive optic neuropathy and a leading cause of blindness in the United States. In glaucoma, vision is lost through apoptosis (programmed cell death) of retinal ganglion cells, a type of cell in the retina that transmits visual information to the brain. Diagnosis of glaucoma is usually based on a combination of progressive, characteristic vision loss (measured using visual field testing) and progressive optic nerve head damage (as detected through dilated fundus examinations or disc photography). While a high pressure inside the eye (ocular hypertension, OHT) is not sufficient for a diagnosis of glaucoma, it is the greatest single risk factor for disease onset.