BIOMECHANICS OF OCULAR PNEUMOPLETHYSMOGRAPHY

A mathematical analysis of ocular pneumoplethysmography is presented, based on the physiological, anatomical, and biomechanical properties o f the eye. Ocular pneumoplethysmography is a clinical procedure involv ing elevation of intraocular pressure, by application of a suction cup to the sclera, to a level that exceeds ophthalmic artery systolic pre ssure. As decay in intraocular pressure is allowed, return of retinal artery pulsations indicates ophthalmic artery systolic pressure. We ob tain a quantitative relationship between increase in intraocular press ure and applied vacuum, and compare the theoretical predictions with e xperiments on rabbits in which a variable descending vacuum was applie d to bilateral scleral eyecups. The bilateral intraocular pressures we re simultaneously recorded from cannulae in the respective vitreous bo dies, and the pressures at which return of ocular pulsations were obse rved were correlated with the scleral vacuums. Regression lines were c alculated for three serial determinations in each animal, with two gro ups of animals distinguished by the inner diameter of the eyecups used . The theoretical results indicate that the relationship between intra ocular pressure increase and applied vacuum is independent of Young's modulus, and depends primarily on the ratio of the diameter of the vac uum cup to the diameter of the eye.