Lorin P. McRae

Oculoplethysmography: An adjunct to arteriography in the diagnosis of extracranial carotid occlusive disease☆

A four and a half year study documents that oculoplethysmography, in conjunction with carotid phonoangiography, fulfills the criteria of an effective noninvasive adjunct to arteriography in the diagnosis of extracranial carotid occlusive disease. The risk and expense of unnecessary arteriographic studies can be reduced and accuracy of arteriographic technics and interpretations can be enhanced by routine application of oculoplethysmography.

Noninvasive detection and evaluation stroke-prone patients.

Multiple perplexities plague the physician in evaluating the patient at risk for stroke because of stroke symptoms, carotid bruits, positive family history, constitutional diseases associated with high incidence of strokes, or age. Current interest in the development of noninvasive diagnostic techniques for evaluating peripheral vascular insufliciency is equaled by interest in the noninvasive detection of surgically remediable, extracranial, carotid occlusive disease.1 An aging population coupled with improved techniques for preventing strokes by carotid endarterectomy further enhances the need for noninvasive, simple, safe, reliable, outpatient techniques to detect the presence of carotid occlusive disease before the onset of a stroke. This need is emphasized by the fact that approximately 25% of frank strokes due to extracranial carotid occlusive disease develop without antecedent cerebral ischemic symptoms.’ The detection of a carotid bruit alerts the astute physician to the possibility of an internal carotid stenosis. But detection of such a bruit does not explain its hemodynamic significance, allow serial follow-up of progressive stenosis, differentiate between external and internal carotid bruits (the former may be as high as 10% of carotid bruits), nor detect the severe stenoses (>85% narrowing) for which the bruit has disappeared. The cost and risk of arteriography are significant deterents to its use for routine screening, for serial follow-up of insignificant carotid lesions, and for studying marginal surgical candidates with a small likelihood of carotid occlusive disease.3

Pressure and volume measurements from the eye for detecting possible arterial obstruction.

Detection and evaluation of functionally significant carotid occlusive disease are effectively achieved by noninvasive pressure and/or volume measurements from the eye. Ocular arterial blood pressure is measured by applying either direct compression or suction to evaluate intraocular pressure to the point of arterial collapse. Carotid blood flow is evaluated as it affects ocular volume waveforms, which result from the difference between pulsatile arterial flow and relatively constant venous flow.The relationship between noninvasive measurements from the eyes and carotid blood flow can be predicted using simple models of the cervical-cerebral circulatory system. Proper models verify clinically observed correlations between pressure and volume measurements from the eye and the underlying carotid occlusive disease. Electrical analog circuits provide a method for varying model parameters to simulate abnormalities, producing waveforms with good similarity to waveforms recorded from patients with known vascular or ophthalmic pathology.Further model refinements can be contributed by interested investigators. By using the improved models the strengths and weaknesses of current tests and techniques can then be better defined. Techniques that have been widely used for screening and evaluating potential stroke patients can thereby be modified to give improved functional analysis of these patients.