Sometimes, especially when performing an eye exam on small children the optometrist will focus a light in the eye. But what does this do? Firstly, this test is a retinoscopy examination, and if you struggle with accurate vision, this is a basic way the optometrist might find out. By looking at the reflection of light off your retina, your optometrist can assess if you are nearsighted, farsighted or have astigmatism. This is how they can also get a pretty good reading on the prescription required to correct your vision.
Basically, what we are looking for during the retinoscopy exam is checking to see how your eye can focus. When light shines into your eye using a retinoscope, a reddish orange light reflects off your retina, through your pupil. This is known as the red reflex. The angle at which the retinoscope's light refracts off your retina, also called your focal length, is the thing that tells us how well your eye can focus. And if we see that you are not focusing properly, 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 corrects the error. That lens power is the prescription you require to rectify your vision with glasses or contact lenses.
The eye doctor will run your exam in a dark or dimmed room. The patient will usually be instructed to look at something behind the doctor. Unlike eye examinations you may have had, you won't be asked to read any 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.