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an instrument for measuring the width or diameter of the pupil.
coreometer(kō″rē-ŏm′ĕ-tĕr) [″ + metron, measure]
An instrument for measuring the pupil.
1. An instrument for measuring the diameter of the pupil. There exist several types but the most common is a series of graduated filled circles whose sizes are compared with the pupil (Haab's pupillometer). It is also common to measure pupil size by photography or video after appropriate calibration of the method (Fig. P25). Syn. coreometer.
2. Although incorrectly used, it refers to an instrument for measuring the interpupillary distance (PD). These instruments are based either on using the pupil centres (e.g. Reichert PD gauge) or the corneal reflections (e.g. Essilor Corneal Reflection Pupillometer; Seiko SP-100 Pupillometer), but the latter can be used on the basis of the pupil centres as well. In the instruments using corneal reflections the subject views the image of a small illuminated target surrounding the observation aperture used by the examiner or made to appear as if it came from the observer's eye. That image is formed at infinity by a lens placed in front of the subject's eyes. The examiner moves a hair line to coincide with the centre of the corneal reflections and reads the monocular and total interpupillary distances. Syn. interpupillometer (this is the most appropriate term for this instrument); PD gauge; PD meter. See PD rule.