Phoropter

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 patient's habitual prescription or an automated refractor may be used to provide initial settings for the phoropter.

Phoroptor is a registered trademark currently owned by Reichert Technologies, filed April 25, 1921, by DeZeng Standard of New Jersey, with the USPTO, serial number 71146698.

DeZeng was purchased in 1925 by American Optical of Massachusetts, which continued to market the product, but the term, often spelled phoropter, has become a generic 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".

There is no evidence this was ever manufactured, but in 1915 he filed for a patent for a binocular version of this same optometer,[4] and called it the Ski-Optometer, so named for its usefulness in doing skiascopy .

It included a Stevens Phorometer for measuring phorias, and a disc of auxiliary spherical lenses on the back, giving it a range of -12.00 to +12.00.

To extend the range, there were clips on the front of each eye hole for the insertion of hand held sphere or cylinder trial lenses, with a mechanism to rotate the axis with the thumb.

Around 1916 Michael Woolf, also of New York City, bought him out and added his own invention,[5] an innovative battery of cylinder lenses, ranging from 0.25 to 2.00 D to the device, as well as Risley prisms for each eye.

Around 1924 the patents and rights were transferred to General Optical Company of Mount Vernon, NY, which had been making a much larger, heavier and more solidly encased instrument, called the Genothalmic Refractor, since around 1920, using Woolf's 1917 patent number, and with a user's manual dated 1921.

It weighed 7 pounds 5 ounces, and unlike all earlier devices of this kind, it hung from a horizontal mounting bar instead of being supported from the bottom.

[2] A refined and improved version of the Genothalmic Refractor was manufactured in London starting around 1932, and sold in the UK by S. R. Stearman, S. Pulzer & Son Ltd., and others, as the British Refracting Unit (B.R.U.).

There were no cylindrical lenses, so testing for astigmatism required the use of manual trial-lenses, for which there were rotating holders on the front of each eye hole, and there were stationary ones on the backs as well.

The forehead rest was removed, and the rear trial lens clips were replaced with rubber eye guards.

588, the AO Wellsworth DeZeng Phoroptor, which was slightly larger; the lenses were increased to 11/16 inch and it weighed 3 lb.

The Greens teamed up with inventor Clyde L. Hunsicker of San Francisco, who applied for a patent on October 25, 1926.

It helped put the Shigon/Woolf/Genothalmic line out of the market and forced AO to completely redesign their phoroptor from scratch, not once, but twice, (the 590 failed to compete).

As for the original Greens' Refractor, in spite of the fact that production stopped decades ago, many are still being used today, as they are virtually indestructible, and have a devoted rank who still swear by them.

[2] Starting in the mid-20th century, companies in Europe and Asia have made phoropters of their own design, as well as copied American models.

The Moeller Wedel Visutest of Germany, the Magnon RT 500 of France, and the Nikon Optester and Takagi MT3, both of Japan, are all of original design.