An automated refraction eye test is one of the ways we can measure how well you can see and helps your optometrist to determine the prescription (lens strength) you need to see clearly. Using a machine called an autorefractor, your optician will get a good idea of the amount of vision correction you need in your glasses or contact lenses. Here, we’ll talk you through how it works.
What is an automated refraction eye test?
Refraction is all about how your eyes bend (or refract) the light entering your eyes. The way they do this determines where light is focused onto the retina at the back of the eye — and therefore how clearly you can see.
How well your eye refracts light is based on three things:
- The shape of your eye (how long or short it is)
- The curvature of your cornea (the clear window at the front of your eye)
- The curvature of your lens (the clear lens in the eye that changes shape to help focus the light onto the retina)
An autorefractor measures how light changes as it comes into the eye and creates a good idea of your prescription. It’s a great starting point for your optician to then carry out the rest of their tests and final refinement of your prescription during your visit. Sometimes, instead of (or in addition to) an autorefractor test, your optician might test refraction manually by performing a retinoscopy.
How does the autorefractor work?
The autorefractor works by projecting an image into your eye. The rays of light from this image pass through the cornea, the pupil and lens of your eye, bounce off the retina, and return through the structures of the eye to a sensor in the autorefractor. The autorefractor then assesses this reflected light beam for any distortions that can happen as a result of a refractive error in the eye.
From this, it calculates an estimation of your prescription with how well your eyes focus on the image and gives an objective measurement of your vision requirements.
What happens during the test?
An automated refraction eye test is usually carried out during the pre-test part of your visit, before you go in to see the optician.
You’ll be asked to sit in front of the machine, put your chin on the rest and look through the two lenses into the machine. You’ll be asked to look at an image, or stay focused on a point of light, while the autorefractor takes its measurements. You won’t need to do anything but keep looking ahead until we’ve got what we need — it’ll only take a few seconds.
The results will be sent through to the optician for them to use during your exam where they’ll carry out a couple more tests manually to make sure you get the most accurate prescription.
What conditions can an autorefractor detect?
An autorefractor detects what are known as refractive errors (causes of blurry vision). These are very common conditions and include:
Short sight (myopia)
Where you struggle to see things far away but can see things closer up clearly. This happens when the eye shape is too long, causing light to focus before it reaches the retina, resulting in blurry vision.
Long sight (hyperopia)
People with long sight struggle to see things up close-up but have clear vision for distance. This can be caused by the eye being too short, the cornea being too flat, or a problem with the ability of the eye’s lens to focus.
People with astigmatism have an irregular shaped cornea. This means that light coming into the eye is focused in more than one place on the retina, causing blurry vision.
Who should be tested for refraction?
Refraction tests are a normal part of an eye test, and everyone will need to have theirs checked regularly to make sure they’re seeing clearly and that their glasses or contact lenses are working for them. We recommend that you come in for an eye test every two years, or sooner if you notice a change in your vision.
Autorefractors are particularly beneficial for people who may have trouble concentrating during a longer exam, or have difficulty clearly describing their vision problems (such as small children, people with dementia, or a mental disability). They can give a quick, highly accurate measurement to determine whether any vision correction is needed, with minimal input.