By direct ophthalmic artery perfusion studies in enucleated cat eyes, volume changes in the intraocular vascular bed were determined after alterations in ophthalmic artery perfusion pressure. Vascular distensibility curves obtained in this manner indicate that the resistance to distension of the intraocular vascular bed increases as its volume increases. A semilogarithmic relationship exists between volume changes in the intraocular vascular bed and alterations of perfusion pressure in the ophthalmic artery. The slope of this relationship, termed the "coefficient of vascular rigidity," is constant at intraocular pressures between 10 and 40 mm Hg. Levarterenol (Levophed) bitartrate does not measurably affect vascular distensibility as measured in this study.
Best M, Blumenthal M, Galin MA. Distensibility of the Intraocular Vascular Bed. Arch Ophthalmol. 1970;84(5):630-634. doi:10.1001/archopht.1970.00990040632015