The effect of an acute elevation of the intraocular pressure (IOP) on the pupil was investigated. It was shown that pupillary dilation occurred when the IOP exceeded diastolic blood pressure and that the dilation was a local phenomenon not due to changes in iris-angle architecture. The pressure necessary to dilate the pupil was shown to coincide with that pressure necessary to inhibit the filling of iris vessels with India ink injected into the arterial system. Systemically administered epinephrine reconstricted a pupil dilated by increased IOP subsequent to the systemic vasopressor response. It was concluded that the pupillary dilation noted in this study and probably that in acute angle-closure glaucoma attacks is secondary to pressure inhibition of blood flow to the iris sphincter muscle.
Charles ST, Hamasaki DI. The Effect of Intraocular Pressure on the Pupil Size. Arch Ophthalmol. 1970;83(6):729-733. doi:10.1001/archopht.1970.00990030729011