Instantaneous tonometry.

Respiration and arterial pulse cause intraocular pressure to cyclically vary around a mean pressure. Both the respiratory and arterial pulse waves approximate sine waves, and we have represented the IOP cycle as the sum of sinusoidal pressure waves. A rapidly acting tonometer may record any portion of the IOP cycle. We have computed the probability that a single pressure measurement will lie within a given interval around mean IOP and the probability that the mean of several such measurements will lie within a given range of mean pressure. The probability that an IOP estimate will lie in a given range of mean IOP decreases as the IOP cycle amplitude increases but increases as the number of tonometric measurements averaged together increases.