There may be various tests that you have experienced at an eye exam and wondered how they work. Having beams of light shined into your eye 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 way light reflects off your retina is one test your eye doctor can employ to see if you need eyeglasses.
In short, what we are looking for during the retinoscopy exam is checking to see how your eye focuses. We begin the exam by looking for what we call the 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, also called your focal length, is exactly what lets us know how well your eye can focus. If it becomes obvious that you aren't focusing properly, that's where the lenses come in. We hold different lenses with varying prescriptions in front of your eye to see which one will correct the refractive error. This is exactly how we calculate the prescription your glasses or contact lenses need to be.
The retinoscopy exam is generally performed in a darkened room. To make your eyes easier to examine, you'll generally be asked to keep your eyes fixed on an object behind the doctor. Because a retinoscopy exam doesn't involve any eye charts, it's also a particularly useful way to determine an accurate prescription for kids who might struggle with speech, or others who might be speech-impaired.