During your eye exam, you may have had a doctor direct a beam of light into your eye, and hold various lenses in front of it. So what does this do? Firstly, this test is a retinoscopy examination, and if you struggle with accurate vision, this is a preliminary way the eye doctor might assess it. By looking at the reflection of light off your retina, the eye doctor can decide whether you are nearsighted, farsighted or have astigmatism, and can also measure the prescription required to correct your vision.
The main thing your doctor is looking for during this exam is how well your eyes can focus. We begin the exam by looking for what's known as 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 retinoscope measures your focal length, or in layman's terms, it will determine the precise 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 becomes obvious that you aren't focusing correctly, that's where the lenses come in. We hold different lenses with varying prescriptions in front of the eye to see which one corrects your vision.
The optometrist will perform your exam in a dark room. To make your eyes easier to examine, you'll generally be asked to look at an object behind the doctor. Unlike eye examinations you may have had, your doctor won't ask you to read letters off charts. This means that a retinoscopy exam is also a very good way to accurately determine the prescriptions of the speech-impaired, or young children.