Eyes as windows on brain pressure.

The eyes are acoustically continuous with the brain and inner ear tissues as regards matched impedances, based on tissue densities; thus, vibration of one site will be reflected in all sites. As a result, the eye reflects the acoustic properties of the brain under pressure, which can be used as a metric of intracranial pressure as demonstrated in a brain/eye balloon model. Further, the model supports the observation that vibration delivered to the eye, if of sufficient intensity, can be perceived as sound, resulting in an eye audiogram similar to that obtained conventionally by bone conduction on the mastoid or forehead. The eye can therefore be considered an acoustical window to the brain and inner ear.