There are a few tests that you may have noticed during an eye exam and asked yourself how they work. Having beams of light shined into your eyes could be an example. Firstly, 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 a way your eye doctor is able to see if you need eyeglasses.
How well your eyes are able to focus under the circumstance we create during the exam is the most important thing we look for. We shine light into your eye because we are looking for what we call your red reflex. The retinoscope aims light into your eye, and a red or orange light reflects through your pupil and off your retina. The angle at which the light refracts off your retina, also called your focal length, is exactly what tells us how well your eye can focus. And if it's apparent that you aren't focusing correctly, that's where the lenses come in. We hold a few prescription lenses in front of your eye to determine which one fixes your vision. That lens power is the prescription you will need to rectify your sight with glasses or contact lenses.
Your eye doctor will run your exam in a dark or dimmed room. To make your eyes easier to examine, you'll generally be instructed to focus on something behind the doctor. Because a retinoscopy exam doesn't involve any eye charts, it's also a particularly useful way to determine an accurate prescription for kids who might struggle with speech, or others who might be speech-impaired.