An applanation tonometer is disclosed for providing a measurement of intraocular fluid pressure inside the eye of a patient. The applanation tonometer includes a light-transmitting prism having a cornea contact tip at one end and a cornea alignment aid at the opposite end. The cornea alignment aid enables the patient to advise a vision professional when a light source of the tonometer is properly aligned with his cornea so that intraocular fluid pressure can be accurately measured. A light-blocking baffle is located at the opposite end of the prism, and a thin light-transmitting channel is formed through the baffle to lie on the longitudinal axis of the prism. In a preferred embodiment, the light baffle is at least one opaque disk, and the light-transmitting channel is a clear spot at the center of the opaque disk through which light is transmitted to the patient's cornea.