There may be various assessments that you have seen during an eye exam and asked yourself what they are for. Having a bright light shined into your eyes could be one of them. This test is known as a retinoscopy examination, and it's a basic way to determine the refractive error of your eye. Whether you're near or farsighted, or you have astigmatism, examining the way light reflects off your retina is one way your eye doctor can see if you need vision correction.
The most important thing your doctor is looking for during this exam is how well your eyes can focus. When we use the retinoscope to shine light into your eye, a reddish orange light reflects off your retina, through your pupil. We call this the red reflex. The degree at which the retinoscope's light reflects off your retina, also called your focal length, is precisely what lets us know how well your eye can focus. And if we notice that you are not focusing well, that's when we use a set of lenses. We hold a variety of lenses with varying prescriptions in front of the eye to see which one fixes the error. And that is exactly how we find out what prescription your glasses or contact lenses need to be.
The optometrist will perform your exam in a dark or dimmed room. The patient will usually be instructed to focus on an object behind the doctor. This makes eyes easier to examine. Unlike other eye exams, you won't be asked to read letters off charts. This means that a retinoscopy exam is also a really good way to accurately determine the prescriptions of the speech-impaired, or young children.