Sometimes, especially when doing an eye exam on a small child the eye doctor will focus a light in the eye. So what does this do? Firstly, this test is a retinoscopy examination, which is a preliminary way to assess the refractive error of your eye. Whether you're near or farsighted, or you have astigmatism, examining the reflection of light off your retina is one way your eye doctor can determine whether you need eyeglasses.
How well your eyes are able to focus under the circumstance we create during the retinoscopy exam is the most important thing we look for. We do this looking for what's known as your red reflex. The retinoscope aims a beam of light into your eye, and a red or orange light reflects through your pupil and off your retina. The angle at which the light reflects off your retina, which is what eye care professionals call your focal length, is exactly what tells us how well your eye can focus. If it becomes clear that you aren't focusing properly, that's when we use a set of lenses. We hold up different lenses with varying prescriptions in front of your eye to determine which one fixes the refractive error. The lens power that works is the prescription you will need to rectify your impairment with glasses or contact lenses.
The retinoscopy exam is performed in a darkened room. The patient will usually be asked to focus on something ahead, just behind the doctor. Unlike other eye exams, you won't be asked to read any charts. This means that a retinoscopy exam is also a very good way to accurately determine the prescriptions of those who may struggle with speech, like young children and the elderly.