Ocular rigidity: Review of measurement methods and its implications in clinical practice

Ocular rigidity is a parameter that characterizes the biomechanical behavior of the eye. Different measurement techniques have been adopted to quantify this parameter. Invasive measurements in experimental animals have provided initial information on the pressure‐volume relation, followed by manometric volumetric and tonographic techniques used in cadaver and living human eyes. Schiotz tonometry with different weights has been employed as a non‐invasive method of quantifying ocular rigidity. Other surrogate measures of ocular rigidity have also been used, incorporating fundus pulsation amplitude and choroidal blood volume. In order to approximate the pressure volume relationship, a variety of different mathematical formulations have been employed. Based on available data, ocular volume, age, intraocular pressure, arterial pressure and ocular blood volume have been identified as parameters that affect ocular rigidity. Moreover, there is mounting evidence in the literature that ocular rigidity may be implicated in the pathogenesis of ocular disease. However, its exact role as well as the underlying pathogenetic mechanisms remain to be elucidated.