There are a few tests that you have seen at an eye exam and wondered how they work. Having beams of light shined into your eye could be one of them. This test is a retinoscopy examination, and if you struggle with accurate vision, this is a preliminary way the eye doctor might find out. Whether you're near or farsighted, or you have astigmatism, examining the way light reflects off your retina is one test your optometrist can employ to see if you need eyeglasses.
How well your eyes are able to focus under the circumstance we create during the retinoscopy exam is really what we're looking for. We shine light into your eye because we are looking for what's known as your red reflex. The retinoscope aims light into your eye, and a red or orange light reflects through your pupil and off your retina. The retinoscope measures your focal length, or in other words, to measure the angle at which light refracts off your retina which tells us how well your eye focuses. And if we notice that you can't focus well, that's where the lenses come in. We hold up several lenses with varying prescriptions in front of the eye to see which one corrects the error. This is precisely how we calculate what prescription your glasses or contact lenses need to be.
Your eye doctor will perform your exam in a dark room. To make your eyes easier to examine, you'll generally be asked to focus on something behind the doctor. Unlike eye examinations you may have had, you won't be asked to read letters off charts. This means that a retinoscopy exam is also a very good way to accurately determine the prescriptions of the speech-impaired, or young children.