To the Editor.—The article by Sand et al (Arch Surg 110:813-818, 1975) conveys the enthusiasm often associated with exaggeration and oversight. The oversight is the failure to recognize that the Gee ocular plethysmodynamography unit cannot determine the systolic pressure of the ophthalmic artery greater than 110 mm Hg (see their Fig 6), which is often present in the hypertensive patient.
Our experience in 261 studies performed since February 1974 is that this represents a serious limitation of the instrument. To offset this limitation, we have employed measurement of the pulse amplitude and pulse delay.
In 16 cases of total occlusion of the internal carotid artery, eight patients had ophthalmic artery pressure (OAP) on the side of occlusion greater than 110 mm Hg. When upright, asymmetry was demonstrated in an additional two patients (success rate, 10 of 16). Asymmetry of pulse amplitude was present in 12 of 16 patients. Pulse