amblyoscope

an instrument for measuring the angle of a squint and assessing the degree to which a person uses both eyes together. It consists of two L-shaped tubes, the short arms of which are joined by a hinge so that the long arms point away from each other. The subject looks into the short end and each eye sees, via a system of mirrors and lenses, a different picture, which is placed at the other end of each tube. If a squint is present, the tubes may be adjusted so that the short arms line up with the direction of each eye.