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Eye care

What Is a Refraction Eye Exam?

The "which is clearer, one or two?" part of an eye exam, explained.

Last updated November 3, 2026 · General information only, not medical advice. Please see a licensed eye-care professional for your prescription and eye health.

Woman wearing glasses

A refraction test determines the lens power that gives you the clearest vision. It is how the SPH, CYL and AXIS values on your prescription are found.

  1. 1

    Starting point

    The examiner may use an autorefractor or retinoscope to estimate your prescription.

  2. 2

    Comparison

    You look through a phoropter at a chart and compare lens options.

  3. 3

    Refinement

    Small changes in power and axis are fine-tuned based on your answers.

A refraction measures your prescription; a comprehensive exam also checks eye health.

This article is general education, not medical advice. For any change in your vision or eye comfort, see a licensed optometrist or ophthalmologist.

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