A set of two prism bars, one for horizontal and one for vertical deviations, each with a rising series of prisms in one bar.
With a prism bar you measure fusional reserves and the size of a squint without changing loose prisms: you move the bar in front of the eye until the eye movement stops. For orthoptic examination in the practice.
Which orthoptic instrument measures what? Read our guide: Orthoptic instruments: what each one measures.
