On occasion, particularly when doing an eye exam on small children the eye doctor will shine a beam of light in the eyes. So what does this do? 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 reflection of light off your retina is one test your eye doctor can employ to determine if you need eyeglasses.
The most important thing your doctor is checking for during this exam is how accurately your eyes can focus. We shine light into your eye because we are looking for what’s known as the red reflex. The retinoscope sends light into your eye, and a reddish light reflects through your pupil and off your retina. We use the light to determine your focal length, or in other words, to calculate the precise angle at which light refracts 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 where the lenses come in. We hold different prescription lenses in front of the eye to see which one rectifies your vision. And that is exactly how we find out the prescription your glasses or contact lenses need to be.
Your optometrist will run your exam in a dark or dimmed room. The patient will usually be told to look at an object behind the doctor. Because a patient doesn’t need to read eye charts during a retinoscopy exam, it means that it’s also a really great way to determine the prescriptions of children or patients who have difficulty with speech.