Phoropters

A phoropter, or refractor, is an ophthalmic instrument used during refraction to determine an eyeglass prescription. It contains a rotating array of lenses, prisms, and sometimes filters that can be positioned in front of the patient's eyes to measure refractive error and assess binocular function.

In a typical examination, the clinician asks the patient to read an eye chart while switching lenses to determine which combination yields the clearest vision. The examiner refines sphere (spherical power), cylinder (cylinder power), and axis for astigmatism, and may use prisms to evaluate eye alignment. A red-green duochrome test may help refine the final spherical power.

Phoropters can be manual, with dials and levers operated by the clinician, or electronic/automatic, where a computer suggests lens combinations and records results. Some units integrate near-vision adds, measurement of pupil distance, and software for data storage and newer workflows. Telephoropters enable remote testing in certain settings.

Phoropters are generally preferred over trial frames for efficiency and consistency, particularly for binocular balance and subjective refinement. They require patient cooperation and clear communication; some individuals, including very young children or those with cognitive challenges, may have limited ability to participate in subjective testing.

Historically, phoropters evolved from early refracting instruments designed to present a fixed set of lenses. Modern devices emphasize rapid, precise control of focus and alignment, and are standard equipment in optometry and ophthalmology clinics worldwide.