phoropter

A phoropter is a diagnostic instrument used by optometrists and ophthalmologists to determine a patient’s refractive error and to refine eyeglass or contact lens prescriptions. It consists of a frame that holds a large selection of lenses, prisms, and other optical elements, which can be rotated into the patient’s line of sight.

During an eye examination, the patient looks through the phoropter at a distant visual target while the clinician changes lenses and asks which option is clearer. This process, known as subjective refraction, is used to measure spherical power for nearsightedness or farsightedness, cylindrical power for astigmatism, and the axis of astigmatism. Prisms may also be used to assess and correct binocular alignment. The device typically includes an occluder to cover one eye and may feature fogging or dialed lens changes to control accommodation.

Modern phoropters range from conventional manual models to motorized and digital systems that can store measurements and allow faster or more precise switching between lens combinations. They are often used in conjunction with autorefractors or keratometry as part of a comprehensive refraction. Cycloplegic refraction may be performed in children to prevent accommodation from affecting results.

Phoropters are standard equipment in optometry and ophthalmology clinics and are essential for determining accurate prescriptions for spectacles or contact lenses, while minimizing patient discomfort and testing time. Proper cleaning and alignment help ensure accurate measurements.