An applanation tonometer and its operation involve an actuator pressing a prism with a variable and determinable force against a cornea of an eye while a source directs light to reflect from an applanation surface of the prism to a detector producing a detected light signal received by a microprocessor. Such a tonometer produces a diastolic phase signal and a systolic phase signal representing the complete intra ocular pressure experience of the eye being examined. The signal information allows combined diastolic and systolic IOP to be determined in several corroborating ways and also yields measures of ocular blood flow and tonography.