There may be a few assessments that you may have noticed at an eye exam and questioned how they work. Having beams of light shined into your eyes could be an example. This is one way we determine the refractive error of your eye, and it's called retinoscopy. Whether you're near or farsighted, or you have astigmatism, examining the way light reflects off your retina is a way your eye doctor can determine if you need eyeglasses.
The main thing an eye doctor is looking for during this exam is how accurately your eyes can focus. When light shines into your eye using a retinoscope, a reddish light reflects off your retina, through your pupil. This is known as the red reflex. The retinoscope measures your focal length, or in simpler words, to calculate the precise angle at which light refracts off your retina. And this is what tells us how well your eye is able to focus. If it's apparent that you can't focus properly, we hold different prescription lenses in front of your eye to determine which one fixes your vision. And that is exactly how we calculate the prescription your glasses or contact lenses need to be.
The eye doctor will perform your exam in a darkened room. To make your eyes easier to examine, you'll usually be told to look at something behind the doctor. Unlike other eye exams, your doctor won't ask you to read any charts. This means that a retinoscopy exam is also a really good way to accurately determine the prescriptions of those who may struggle with speech, like young children and the elderly.