Doppler ultrasound of orbital vessels.

The techniques of doppler ultrasound have been applied to blood vessels within the orbit. The doppler frequency shifts of ultrasonic pulses scattered from blood cells moving within orbital vessels are a measure of velocities rather than the amount of blood flow. The doppler signal from the ophthalmic artery behind the globe is responsive to changes in ocular blood flow. Blood flow can also be detected at the optic nerve head, and from the coats of the eye adjacent to the nerve head. Flow rate in the ophthalmic artery is reduced following retrobulbar anaesthesia. The source of the pulsatile retrograde flow signal which can be detected in some cases of internal carotid stenosis is located in the region of the ophthalmic artery.