Measurement of Internal Carotid Artery Blood Volume Pulsations by Noncontact Ocular Photoelectric Plethysmography

The goal of this investigation is to develop a noninvasive technique to assess the patency of the internal carotid artery. A noncontact photoelectric plethysmograph was designed to measure intraocular blood volume pulsations. This technique is appropriate for an evaluation of carotid stenosis since the ophthalmic artery is a branch of the internal carotid. With this noncontact instrument a beam of light is passed from a photoelectric system through the pupil. Light is reflected from the retinal and choroidal vasculature and is detected by a photodetector. This instrument has been used successfully in a series of experiments with pigmented and albino rabbits. The results demonstrate that the instrument measures the light reflected from the intraocular vasculature by the following observations: 1) an occlusion of the ca-rotid artery causes a disappearance of the ocular pulse; and 2) the amplitude of the ocular pulse is smaller in the pigmented rabbit when compared with the albino rabbit. Ocular movement artifacts and low reflected signal amplitude (due to light absorption by the retinal pigment) may necessitate the use of signal analysis techniques in patient studies.