Effect of sympathetic stimulation on critical closure of intraocular blood vessels.

Acute common carotid occlusion in rabbits causes a reduction in ocular blood volume and ciliary artery blood pressure. At all levels of intraocular pressure, cervical sympathetic stimulation reduces these changes. The ocidar blood volume reduction after acute common carotid occlusion is not linearly related to the absolute blood pressure change or to the lowest blood pressure reached in the ciliary artery; it is related to the effective perfusion pressure after occlusion. Effective perfusion pressure is equal to ciliary artery blood pressure minus intraocular pressure and it reflects the transmural pressure of ocular blood vessels.. The effective perfusion pressure at which the peak ocular volume change occurs after acute common carotid occlusion reflects the critical closing pressure of the ocular blood vessels. This approaches zero in the absence of sympathetic stimulation and is 10 mm. Hg or greater in the presence of sympathetic stimulation.