There are various assessments that you have experienced at an eye exam and asked yourself how they work. Having beams of light shined into your eyes may be one of them. This test is known as a retinoscopy examination, and if you have problems with accurate vision, this is one way the optometrist might assess it. Whether you're near or farsighted, or you have astigmatism, examining the reflection of light off your retina is one test your eye doctor can employ to see if you need vision correction.
Essentially, what we are doing during a retinoscopy exam is checking how accurately your eye focuses. We begin the exam by looking for what we call your red reflex. The retinoscope sends light into your eye, and a red or orange light reflects through your pupil and off your retina. The retinoscope measures your focal length, or in simpler words, to measure the angle of refraction of light off your retina. And this is what lets us know how well your eye is able to focus. If it's apparent that you can't focus well, that's when we use a set of lenses. We hold up a few prescription lenses in front of the eye to determine which one rectifies the error. That lens power is the prescription you require to correct your impairment 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 instructed to focus on an object behind the doctor. Because a patient isn't required to read eye charts during a retinoscopy exam, it means that it's also a really great way to determine an accurate prescription for children or patients who have difficulty with speech.