Also found in: Dictionary, Encyclopedia, Wikipedia.
an instrument for evaluation of vision, with lenses placed on dials in a unit that is positioned in front of the patient. See illustration.
The instrument used to measure refractive status of the eyes. It contains many lenses which are then changed in front of the eyes while the patient is looking at an eye chart. This is when the doctor usually asks, "Which is better, one or two?"
Mentioned in: Visual Impairment
An instrument for measuring the ametropias, phorias and the amplitude of accommodation of the eyes. It consists of a large unit placed in front of the patient's head in which there are three rotating discs containing convex and concave spherical and cylindrical lenses, as well as occluders, Maddox rods, pinholes, Polaroids, prisms and coloured filters. An attachment on the instrument allows sets of rotary prisms and cross-cylinders to be swung in front of each sight hole (Fig. P9). Syn. refracting unit; refractor; refractor head. See Simultantest; trial case.