There may be various tests that you have experienced during an eye exam and asked yourself how they work. Having beams of light shined into your eyes may be an example. This test is a retinoscopy examination, and it's a basic way to assess the refractive error of your eye. Whether you're near or farsighted, or you have astigmatism, examining the reflection of light off your retina is a test your optometrist can employ to determine whether you need vision correction.
In short, what we are looking for during a retinoscopy exam is checking how accurately your eye can focus. We shine light into your eye because we are looking for what we call your red reflex. The retinoscope sends light into your eye, and a red or orange light reflects through your pupil and off your retina. We use the light to determine your focal length, or in layman's terms, it will measure the precise angle of refraction of light off your retina. And this is what tells us how well your eye focuses. And if it's apparent that you can't focus correctly, that's when we use a set of lenses. We hold different prescription lenses in front of your eye to determine which one rectifies the error. The lens power that works is the prescription you require to rectify your impairment with glasses or contact lenses.
Your eye doctor will run your exam in a dark room. To make your eyes easier to examine, you'll generally be told to keep your eyes fixed on something behind the doctor. Because a patient isn't instructed to read eye charts during a retinoscopy exam, it means that it's also a really great way to determine an accurate prescription for kids who might struggle with speech, or others who might be speech-impaired.