During some eye exams, you may have had a doctor ask you to look straight in front of you while shining a strong light into your eye. But why? Such as test is used to help test the refractive error of your eye, and it's known as a retinoscopy exam. It sounds fascinating, but by looking at the reflection of light off your retina, the optometrist can determine whether you are nearsighted, farsighted or have astigmatism, and can also measure the prescription you would need to correct your vision.
In short, what we are looking for during the retinoscopy exam is checking how well your eye focuses. We do this 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 other words, to measure the precise angle of refraction of light off your retina. And this is what tells us how well your eye focuses. And if we see that you can't focus correctly, that's when we use a set of lenses. We hold up a variety of lenses with varying prescriptions in front of your eye to see which one rectifies your vision.
All this happens in a dark room. To make your eyes easier to examine, you'll usually be told to look at something behind the doctor. Because a retinoscopy exam doesn't require you to read eye charts, it means that it's also a really great way to determine the prescriptions of children or patients who have difficulty with speech.