There may be some assessments that you may have noticed during an eye exam and asked yourself what they measure. Having beams of light shined into your eyes may be one of them. Such as test is used to help determine the refractive error of your eye, and it's called retinoscopy. Whether you're near or farsighted, or you have astigmatism, examining the reflection of light off your retina is one way your eye doctor is able to see whether you need vision correction.
How well your eyes focus during the exam is really what we're looking for. We shine light into your eye because we are looking for what we call the red reflex. The retinoscope sends light into your eye, and a reddish light reflects through your pupil and off your retina. The degree at which the light reflects off your retina, also called your focal length, is exactly what lets us know how well your eye can focus. If it's apparent that you can't focus well, that's when we use a set of lenses. We hold a variety of lenses with varying prescriptions in front of the eye to see which one fixes your vision.
All this happens in a darkened room. To make your eyes easier to examine, you'll usually be told to look at something behind the doctor. Not having to read any eye charts means that a retinoscopy exam is also a really good way to accurately determine the prescriptions of those who may struggle with speech, like young children and the elderly.