There may be various assessments that you have experienced at an eye exam and questioned how they work. Having beams of light shined into your eye could be an example. This is one way we test the refractive error of your eye, and it's known as retinoscopy. It sounds fascinating, but by looking at the way light reflects off your retina, the optometrist 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.
Basically, what we are doing during the retinoscopy exam is checking how accurately your eye can focus. We begin the exam by looking for what we call the red reflex. The retinoscope sends light into your eye, and a reddish light reflects through your pupil and off your retina. This process measures your focal length, or in simpler words, to determine the precise angle at which light refracts off your retina which lets us know how well your eye is able to focus. If it's apparent that you can't focus correctly, we hold different prescription lenses in front of your eye to determine which one fixes your vision. The lens power that works is the prescription you will need to rectify your vision with glasses or contact lenses.
All this happens in a darkened room. You will usually be instructed to focus on something ahead, just behind the doctor. This makes eyes easier to examine. Because a retinoscopy exam doesn't require you to read eye charts, it means that it's also a really great way to determine an accurate prescription for kids who might struggle with speech, or others who might be speech-impaired.