Sometimes, especially when doing an eye exam on a small child the optometrist will direct a light in the eyes. But why? 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 way light reflects off your retina is a way your optometrist is able to see whether you need vision correction.
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 we call your red reflex. The retinoscope aims light into your eye, and a reddish light reflects through your pupil and off your retina. The retinoscope measures 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 is able to focus. And if it’s apparent that you are not focusing correctly, we hold different lenses with varying prescriptions in front of the eye to determine which one will correct the refractive error. And that is precisely how we find out the prescription your glasses or contact lenses need to be.
Your retinoscopy exam is usually performed 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. Not having to read any eye charts means that a retinoscopy exam is also a very good way to accurately determine the prescriptions of those who may struggle with speech, like young children and the elderly.