Phoropter

Phoropter is a common name for an ophthalmic testing device, also called a refractor. It is commonly used by eye care professionals during an eye examination, and contains 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. It also is used to measure the patients' phorias and ductions, which are characteristics of binocularity. Phoropter is a common name for an ophthalmic testing device, also called a refractor. It is commonly used by eye care professionals during an eye examination, and contains 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. It also is used to measure the patients' phorias and ductions, which are characteristics of binocularity. 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. The patient's habitual prescription or an automated refractor may be used to provide initial settings for the phoropter. Sometimes a retinoscope is used through the phoropter to measure the vision without the patient having to speak, which is useful for infants and people who don't speak the language of the practitioner. Phoropters can also measure Heterophorias (natural resting position of the eyes), accommodative amplitudes, accommodative leads/lags, accommodative posture, horizontal and vertical vergences, and more. The major components of the phoropter are the battery of spherical and cylindrical lenses, auxiliary devices such as Maddox rods, filtered lenses, prisms, and the JCC (Jackson Cross-Cylinder) used for astigmatism measurement. The prismatic lenses are used to analyze binocular vision and treat orthoptic problems. From the measurements taken, the specialist will write an eyeglass prescription that contains at least 3 numerical specifications for each eye: sphere, cylinder, and axis, as well as pupillary distance (distance between eyes), and, rarely, prism for one or both eyes. The lenses within a phoropter refract light in order to focus images on the patient's retina. The optical power of these lenses is measured in 0.25 diopter increments. By changing these lenses, the examiner is able to determine the spherical power, cylindrical power, and cylindrical axis necessary to correct a person's refractive error. The presence of cylindrical power indicates the presence of astigmatism, which has an axis measured from 0 to 180 degrees away from being aligned horizontally. Phoropters are made with either plus or minus cylinders. Traditionally, ophthalmologists and orthoptists use plus cylinder phoropters and optometrists use minus cylinder phoropters. One can mathematically convert figures obtained from either type of phoropter to the other. Phoroptor is a registered trademark currently owned by Reichert Technologies, filed Apr 25, 1921 by DeZeng Standard of New Jersey, with the USPTO, serial number 71146698. The word was coined at that time for the newest version of their phoro-optometer. DeZeng was purchased in 1925 by American Optical of Massachusetts, who continued to market the product, but the term, often spelled phoropter, has become a genericised trademark for all brands of modern vision testers, especially since AO's main competitor, Bausch and Lomb, stopped making their Greens' Refractor in 1970s. Reichert bought AO's refracting equipment division in 1980s, and their current version is named 'Ultramatic Rx Master Phoroptor'. The history of the phoropter, as a binocular refracting device which can also measure phorias, ductions, and other traits of binocularity, as distinct from the monocular optometer, which cannot, starts in the mid-1910s, with the introduction of the Ski-optometer by Nathan Shigon, and the Phoro-optometer by Henry DeZeng. These two inventions, as they continued to improve, were accompanied by a third device, the Greens' Refractor, which entered the market in 1934. European manufacturers were working on similar devices as well.