There may be some assessments that you may have noticed at an eye exam and questioned what they measure. Having beams of light shined into your eyes may be an example. This is one way eye doctors determine the refractive error of your eye, and it's known as a retinoscopy exam. Whether you're near or farsighted, or you have astigmatism, examining the reflection of light off your retina is a way your optometrist is able to see if you need vision correction.
Basically, what we are looking for during the retinoscopy exam is checking how well your eye focuses. We do this looking for what's known as your red reflex. The retinoscope aims a beam of light into your eye, and a reddish light reflects through your pupil and off your retina. The degree at which the retinoscope's light refracts off your retina, which is what eye care professionals call your focal length, is the thing that lets us know how well your eye can focus. And if we see that you can't focus properly, we hold several prescription lenses in front of the eye to determine which one fixes your vision. This is exactly how we calculate the prescription your glasses or contact lenses need to be.
All this happens in a dark or dimmed room. To make your eyes easier to examine, you'll generally be instructed to keep your eyes fixed on an object behind the doctor. Because a retinoscopy exam doesn't require you to read eye charts, it's also a particularly useful way to determine an accurate prescription for children or patients who have difficulty with speech.