Static and dynamic measurements of the pressure-volume relationship in living and dead rabbit eyes

Abstract

Measurements of the relationship between intraocular pressure and volume were made in eyes of living and dead rabbits. The measurements were made with a newly developed apparatus that controls intraocular pressure by servo means and meters the volume of fluid passing to or from the eye through a cannula connection to the eye. After establishing steady-state conditions the static pressure-volume relationship was determined by measuring the volume changes resulting from step changes in pressure. The dynamic pressure-volume relationship was determined by measuring the oscillatory volume changes of the eye in response to small sinusoidal pressure variations above and below the selected mean intraocular pressures. The pressure-volume relationship measured by dynamic means differs significantly from that measured by static means, a difference we ascribe to the viscoelastic nature of the eye coats. Using either measurement method, the pressure-volume relationship in the living rabbit eye differs significantly from that in the dead rabbit eye, a difference we attribute to the effect of the intraocular vascular system. Based on these results, we estimated the error that may occur in calculating the facility of outflow from tonographic data when the effects of blood volume and viscoelastic changes are neglected. The error was found to be relatively small.