Sometimes, particularly when performing an eye exam on a small child the optometrist will focus a light in the eyes. So what does this do? This test is known as a retinoscopy examination, which is a preliminary way to measure 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 determine if you need eyeglasses.
How well your eyes are able to focus under the circumstance we create during the exam is really what we're looking for. When we use the retinoscope to shine light into your eye, a reddish orange light reflects off your retina, through your pupil. Eye doctors call this the red reflex. The angle at which the light reflects off your retina, also called your focal length, is exactly what lets us know how well your eye can focus. And if it's apparent that you can't focus correctly, we hold different prescription lenses in front of the eye to see which one will correct the refractive error.
All this happens in a darkened room. The patient will usually be instructed to look at something behind the doctor. Unlike other eye exams, your doctor won't ask you to read letters off charts. This means that a retinoscopy exam is also a very useful tool to determine the prescriptions of those who may struggle with speech, like young children and the elderly.