An A-scan ultrasound system is described which allows visualization along the ultrasonic path to assure alignment with the patient's visual axis. A special "sound collimator" produces a 2-mm beam from a 10-megacycle transducer which is aimed through a water column and eye cup mounted in such a way as not to cause contact deformation of the globe. Measurements are made from gated portions of the signal with an electronic interval counter and a photographic record is taken.
COLEMAN DJ, CARLIN B. A New System for Visual Axis Measurements in the Human Eye Using Ultrasound. Arch Ophthalmol. 1967;77(1):124-127. doi:10.1001/archopht.1967.00980020126027