Milton Best

THE OCULAR PULSE — TECHNICAL FEATURES

Ocular techniques to study carotid occlusive disease include ophthalmodynamometry, carotid compression-tonography, and ocular pulse measurements. Studies using this latter method have been concerned primarily with the amplitude of the recorded pulse, and it has been noted that a reduction in amplitude of the ocular pulse occurs on the side of carotid occlusive disease (Castren et a2. 1964, B y n k e 1966, 1968a, 1968b, and 1969, B y n k e and Krakau 1964, Lester 1966, Bron et al. 1967, Galin et al. 1967b). Changes in the contour of the ocular pulse recordings have not received much attention although contour analysis has been of great importance in peripheral vascular disease (Winsor 1959). Ocular pulses recorded from the surface of the eye with a suction cup are similar in all respects to pulses recorded by direct cannulation and reflect the pressure changes occurring in the eye during the cardiac cycle (Lawrence et al. 1966). This report concerns itself with a consideration of the suction technique used to record ocular pulses and the effects of various physical factors upon the pulse amplitude, peak characteristics and notching.

VOLUMETRIC STUDIES OF OPHTHALMIC ARTERY PERFUSION PRESSURE AND OCULAR RIGIDITY

Although Friedenwald postulated a constant ocular pressure-volume relationship over a wide range of intraocular pressures (1937), a number of studies have indicated the variability of this relationship (Perkins & Gloster 1957, Macri et al. 1957, Ytteborg 1960, Eisenlohr & Langham 1962). One component of this variable relationship may be due to alterations that occur in scleral elasticity as the tension in the ocular coats is changed with alterations in intraocular pressure (Gloster, Perkins & Pommier 1957). In addition, changes in intraocular blood volume a t different intraocular pressures may play an important role in the pressure-volume relationship (Ytteborg 1960). Attempts to study the effect of ocular blood volume on this relationship, however, have yielded inconsistent results, perhaps because inadequate attention was paid to the measurements of perfusion pressure in the ocular vascular bed (Ytteborg 1960, Eisenlohr & Langham 1962, Pollack & Becker 1961, Best, Pola & Galin 1969). Previous studies from this laboratory using manometric techniques indicated that there is an inverse relationship between ocular rigidity and ophthalmic artery perfusion pressures between 40 and 100 mm Hg (Blumental, Best & Galin 1970). Although ocular volume changes in this study were induced with a to-

THE NATURE OF THE OCULAR PULSE

THE EYE HAS FREQUENTLY been blamed for headache, with little justification in most instances.1,2 Though refractive errors and aniseikonia are common, they are not often causes for headache. In fact, measurements of this latter state are now rarely performed. Persistent contraction of the ciliary body, however, which occurs in hyperopia and presbyopia can, particularly when associated with convergence effort, result in asthenopia and headache.

ELASTIC PROPERTIES OF INTRAOCULAR BLOOD VESSELS

The pressure‐flow relationship of the intraocular vascular bed was determined by direct perfusion of the ophthalmic artery in enucleated cat eyes. From the data obtained, pressure‐resistance, pressure‐radius, and tensionradius diagrams were constructed for the resistance vessels of the intraocular vascular bed. The results indicated that these vessels do not obey Hookes law in that Youngs modulus of elasticity increases as the radius of the vessel is increased. The shape of the elastic diagram is not affected by alterations in intraocular pressure or vasomotor tone. The addition of levarterenol bitartrate to the perfusate increases critical closing pressure and resistance but decreases circumferential tension in the vessel wall by causing a marked reduction in the radius of the vessel.

Intraocular pressure and common carotid occlusion.

A semilogarithmic relationship has been established between changes in intraocular pressure and ocular vascular volume after acute common carotid occlusion. This relationship has been used to derive a series of equations that relate the ocular blood volume change after acute common carotid occlusion and the resultant pressure changes in the intraocular vascular compartment by a theoretical constant termed the coefficient of vascular rigidity and a variable, Pco, that reflects the pressure dynamics in the carotid system after acute carotid occlusion. A method for estimating Pco in patients using multiple weight carotid compression tonography is described. Pco was found to vary from normal values in patients with chronic cerebrovascular disease.