There may be some tests that you may have noticed during an eye exam and asked yourself what they are for. Having a bright light shined into your eye could be one of them. This is one way eye doctors test the refractive error of your eye, and it’s called retinoscopy. By just looking at the reflection of light off your retina, the optometrist can determine whether 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.
How well your eyes are able to focus during the retinoscopy exam is the most important thing we look for. When we use the retinoscope to shine light into your eye, a reddish light reflects off your retina, through your pupil. This is known as the red reflex. We use the light to measure your focal length, or in other words, to measure the precise angle at which light refracts off your retina which tells us how well your eye focuses. And if we see that you can’t focus correctly, we hold a number of lenses with varying prescriptions in front of the eye to see which one fixes the refractive error. That lens power is the prescription you require to rectify your sight with glasses or contact lenses.
All this happens in a dark or dimmed room. The patient will usually be asked to look at an object behind the doctor. This makes eyes easier to examine. The exam doesn’t include charts to be read, which means that a retinoscopy exam is also a really useful tool to determine the prescriptions of those who may struggle with speech, like young children and the elderly.