There are various tests that you may have noticed at an eye exam and questioned how they work. Having beams of light shined into your eyes could be an example. Firstly, this test is known as a retinoscopy examination, and if you struggle with accurate vision, this is one way the eye doctor could assess it. By examining the reflection of light off your retina, your eye care professional can assess 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 focus during the retinoscopy exam is the most important thing we look for. We do this looking for what we call the red reflex. The retinoscope aims a beam of light into your eye, and a reddish light reflects through your pupil and off your retina. The degree at which the light refracts off your retina, also called your focal length, is the thing that lets us know how well your eye can focus. If it becomes clear that you can't focus properly, we hold up a variety of prescription lenses in front of the eye to see which one fixes the error. The lens power that works is the prescription you require to fix your vision with glasses or contact lenses.
These exams are usually performed in a darkened room. To make your eyes easier to examine, you'll generally be asked to keep your eyes fixed on an object behind the doctor. Unlike eye examinations you may have had, you won't be asked to read any charts. This 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.