Optometer (ophthalmic instrument)

The optometer was a device used for measuring the necessary spherical and/or cylindrical corrections to be prescribed for eyeglasses, from the middle of the 18th century until around 1922, when modern instruments were developed.

"Phoropter" is one of several generic names for modern instruments containing an optometer for each eye (battery of lenses for determination of optical error), combined with prisms and other attachments for measuring binocularity.

[5] In the middle of the 19th century, doctors tested for optical error using single hand-held lenses, held one at a time in front of the patient's eye, or in a trial frame.

In the later part of the 19th century, the United States, Germany, France and the UK were actively inventing numerous mechanical optometers, to speed up the process of bringing lenses before the patients' eyes.

Optometer was the generic name for devices, crude and simple, with rotating batteries of sphere and cylinder lenses placed in front of each eye, one at a time; so there was no testing for binocularity.