Phoropter

A phoropter can measure refractive error to determine an individual's spectacle lens prescription during an eye examination.

A phoropter 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.^[1]

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.

Phoropters can also measure phorias (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 JCC (Jackson Cross-Cylinder) used for astigmatism correction, Risley prisms to measure phorias and vergences, and the (+), (−), and cylinder lenses.

From the measurements taken, the specialist will write an eyeglass prescription that contains at least 6 numerical specifications (3 for each eye): sphere, cylinder, and axis and possibly pupillary distance.

A simple trial frame is used with a retinoscope to determine refractive errors. Lens of varying focal lengths may be placed in the trial frame. Trial frames, such as in this picture, are not to be mistaken for phoropters.

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.

The phoropters also include prismatic lenses which are used to analyze binocular vision and treat orthoptic problems.

Trademark

Phoroptor is a registered trademark name currently owned by Reichert Technologies, filed Apr 25, 1921 with the USPTO, serial number 71146698. The common name is refractor. The current version is named "Ultramatic RX Master Phoroptor".

See also

• Ophthalmic lens
• Ophthalmologist
• Optometrist
• Orthoptist

References

1. ^ Dictionary.com, Definition of "phoropter", American Heritage Stedman's Medical Dictionary. Retrieved 10-10-10.