A small hand-held electronic machine that is sometimes used to check eye pressure. While not as accurate as other methods, the Tono-Pen is useful for the bedridden and people who can’t get up to the microscope for more traditional pressure measurements. To use the Tono-Pen, the eye is numbed with anesthetic drops and the device is gently tapped against the front of the cornea. This doesn’t hurt, but feels a little odd. Sterile rubber covers (they look like rubber balloons or miniature condoms) are applied to the Tono-Pen to keep the procedure completely sterile.