A phoropter (compare with Phoroptor: a trademarked name by Reichert for
their range of phoropters) is an instrument commonly used by eye care
professionals during an eye examination, containing different lenses
used for refraction of the eye during sight testing, to measure an
individual's refractive error and determine his or her eyeglass
prescription. Typically, the patient sits behind the phoropter, and
looks through it at an eye chart placed at optical infinity (20 feet or 6
metres), then at near (16 inches or 40 centimetres) for individuals
needing reading glasses. The eye care professional then changes lenses
and other settings, while asking the patient for subjective feedback on
which settings gave the best vision. Sometimes a retinoscope or an
automated refractor is used to provide initial settings for the
phoropter.
