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 eye refraction 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)
During your refraction, your optician will introduce different combinations of lenses in front of your eyes and ask you which gives you the best vision. This allows your optician to establish the best prescription for you.
What is an autorefractor?
An autorefractor is a machine that opticians use to measure how light changes as it comes into the eye, giving an accurate estimate 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, particularly when testing children, instead of (or in addition to) an autorefractor test, your optician might perform refraction by shining a light into your eyes from a distance, this is called 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 the 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 provides an accurate estimation of your prescription.
How is autorefraction done?
Autorefraction 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 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. It does this by making the picture appear closer and further away; as it does this, it estimates your prescription by how well your eyes focus on the image. 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 is the difference between an eye exam and refraction?
Refraction is a normal part of the eye exam process. An initial refraction usually takes place in store as part of the pre-test before you go in to see the optician, using a machine called an autorefractor. Once you’re in the consulting room your optician will fine-tune these results to ensure you have the most accurate prescription.
An important part of a refraction is reading the letters from a Snellen or letter chart — the test that most people think of when they think of eye tests. Other types of tests you might be familiar with are the Ishihara test for colour blindness — more information can be found on our pages.
What conditions can an autorefractor detect and measure?
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 is too long, causing light to focus before it reaches the retina, resulting in blurry vision.
Who should be tested with an autorefractor?
Refractions are a normal part of an eye test used to work out your prescription. Everyone will need to have their prescription 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.
You can learn more about the tests we use during your visit on our eye test hub, or if it’s time for your next eye test, you can book an appointment online.