In Reply.—Dr Carney is correct in his observation that the Gee unit cannot determine the systolic pressure of the ophthalmic artery greater than 110 mm Hg. I disagree with his assumption that this represents a serious limitation of the instrument. In over 700 studies performed since July 1971, fifty-nine patients with documented unilateral carotid occlusion have been encountered. In 57 of the 59 patients, the ophthalmic systolic pressure on the side of the occlusion was below 110 mm Hg. In the two patients in whom the ophthalmic systolic pressures from both eyes exceeded 110 mm Hg, the calibrated pulse amplitude from the eye distal to the occluded artery was distinctly lower than that from the contralateral eye. Both of these patients had systemic systolic pressures in excess of 200 mm Hg. High speed recording, as suggested by Dr Carney, is not necessary for clinical application.
The design and performance