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A phoropter is an instrument used during an eye examination to measure your refractive error and determine the appropriate prescription for your eyeglasses or contacts.

The apparatus accomplishes this task using a variety of lenses. The patient looks through the phoropter at an eye chart. This chart is placed at several different locations, including optical infinity (20 feet) and at a near position (16 inches) to evaluate farsightedness.

An eye doctor will alter the lenses and settings of the phoropter while prompting the patient to provide feedback on how clear his or her vision is at each setting. The eye doctor will determine the appropriate prescription based on the patient’s feedback.

The eyeglass prescription generated by the phoropter will contain three numerical specifications for each eye: one for sphere, one for cylinder, and one for axis.

Other Uses of Phoropters

Phoropters can also be used to measure:

  • The natural resting position of the eye
  • Accommodative amplitudes
  • Accommodative leads/lags
  • Accommodative posture
  • Horizontal and vertical vergences

How Phoropters Work

Phoropters contain three major components:

  • The JCC (Jackson Cross-Cylinder) evaluates refractive errors caused by astigmatism
  • Risley prisms measure the natural resting position of the eye and vergences
  • The (+), (-), and cylinder lenses

The phoropter lenses refract light, focusing images on the patient’s retina. These lenses increase in power by 0.25 diopter increments. As the lenses are changed, the eye doctor can evaluate the spherical power, cylindrical power, and cylindrical axis needed to accommodate for the patient’s refractive error.

Phoropters contain either plus or minus cylinders. Plus cylinders phoropters are typically used by ophthalmologists, while minus cylinder phoropters are commonly used by optometrists.

To learn more about ophthalmic technology or to schedule an eye examination, please contact an eye doctor near you.

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