During an eye examination, you may have had a doctor direct a beam of light into your eye, and hold various lenses in front of it. But what does this do? This is one way we determine the refractive error of your eye, and it's called a retinoscopy exam. It sounds fascinating, but by examining the reflection of light off your retina, your optometrist can assess whether you are nearsighted, farsighted or have astigmatism, and can also get a pretty good reading on the prescription required to correct your vision.
How well your eyes focus during the retinoscopy exam is really what we're looking for. When we use the retinoscope to shine light into your eye, a reddish orange 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 exactly what tells us how well your eye can focus. And if it's apparent that you can't focus correctly, that's where the lenses come in. We hold a few lenses with varying prescriptions in front of your eye to determine which one fixes the refractive error.
All this happens in a dark or dimmed room. To make your eyes easier to examine, you'll usually be told to look at something behind the doctor. Because a patient isn't required to read eye charts during a retinoscopy exam, it's also a particularly useful way to determine the prescriptions of kids who might struggle with speech, or others who might be speech-impaired.