During an eye examination, you may have had a doctor instruct you to look ahead while shining a beam of light into your eye. But why? Firstly, this test is a retinoscopy examination, and if you struggle with accurate vision, this is a basic way the eye doctor might assess it. By examining the way light reflects off your retina, the eye doctor can decide if you are nearsighted, farsighted or have astigmatism. This is how they may also measure the prescription you would need to correct your vision.
How well your eyes are able to focus under the circumstance we create during the retinoscopy exam is really what we're looking for. 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. We use the light to determine your focal length, or in other words, to determine the precise angle at which light refracts off your retina. And this is what lets us know how well your eye focuses. If it becomes clear that you can't focus properly, that's where the lenses come in. We hold up a variety of prescription lenses in front of the eye to see which one fixes your vision. The lens power that works is the prescription you require to correct your vision with glasses or contact lenses.
All this happens in a dark or dimmed room. To make your eyes easier to examine, you'll usually be asked to keep your eyes fixed on something behind the doctor. Unlike eye examinations you may have had, you won't be asked 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.