The measurement of intraocular pressure is perhaps the most important clinical parameter contributing to the diagnosis of glaucoma. This report describes the most commonly used methods of tonometry (to measure intraocular pressure). Considering the common options of Goldmann applanation tonometry (GAT), Schiotz tonometry (ST), and Tono-Pen tonometry (TP), the TP is the easiest to use in the emergency department. It is subject to some degree of inaccuracy. In the pediatric emergency department, a child with a painful eye is likely to require deep sedation to achieve an accurate measurement.