An improved applanation tonometer for measuring the intraocular pressure of an eye is configured for use with a conventional slit lamp. This applanation tonometer has a force sensor that senses the force applied by an applanation probe to flatten the cornea of the eye, while the cornea is viewed through the probe using the slit lamp. The force sensor generates a signal that corresponds to the applanation force and transmits the signal to a display and/or a data storage device.