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.
Phoropters can also be used to measure:
Phoropters contain three major components:
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.