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How Retinoscopy Works

On occasion, particularly when doing an eye exam on a small child the optometrist will focus a beam of light in the eye. But why? This test is called a retinoscopy examination, and it's a basic way to assess the refractive error of your eye. By examining the reflection of light off your retina, your eye doctor can determine whether you are nearsighted, farsighted or have astigmatism, and can also measure the prescription required to correct your vision.

How well your eyes focus during the exam is the most important thing we look for. When light shines into your eye using a retinoscope, a reddish light reflects off your retina, through your pupil. This is called the red reflex. The degree at which the retinoscope's light reflects off your retina, also called your focal length, is precisely what tells us how well your eye can focus. If it's apparent that you can't focus well, we hold a variety of lenses with varying prescriptions in front of your eye to determine which one will correct the refractive error. And that is exactly how we calculate what prescription your glasses or contact lenses need to be.

The eye doctor will run your exam in a dark or dimmed room. To make your eyes easier to examine, you'll usually be told to keep your eyes fixed on something behind the doctor. Because a retinoscopy exam doesn't involve any eye charts, it's also a particularly useful way to determine the prescriptions of children or patients who have difficulty with speech.