What is retinoscopy?
Retinoscopy is a test used by opticians to measure how well you can see objects at varying distances and determines the kind of vision correction you’d need for your glasses. It measures for what’s known as a refractive error, which causes blurry vision, and covers common conditions like short sight, long sight and astigmatism.
The test is performed using a small, handheld instrument called a retinoscope. It resembles a small periscope and often has a metallic handle; a sleeve which moves up and down the middle part of its shaft and is used to sharpen (converge) or soften (diverge) a beam of light; and a black upper section, or head, which the optometrist looks through to examine your eyes.
When is retinoscopy used?
Retinoscopy gives your optometrist an objective measure of your eyesight — which means that the procedure and its findings are not dependent on any response from the person being examined. This makes it an ideal test for people who may have a trouble communicating, such as young children or those with speech difficulties. Retinoscopy is also often used for people with dementia who might find it difficult to articulate or explain their symptoms to an optician.
Optometrists may perform a retinoscopy as a preliminary test in order to ensure they get the most accurate reading for your prescription. After a retinoscopy, they will usually carry out a subjective refraction test that relies on your response, such as a Snellen test. Your optometrist will then use a combination of these two test results to decide on the right prescription for you.
As well as manual retinoscopy, sometimes an automated refraction test might be used to test your vision digitally, before you see the optician.
How is a retinoscopy performed?
A retinoscopy is part of your regular eye test and is performed in a darkened examination room. You will be seated comfortably, with the optometrist sitting opposite you about an arm’s length away. The optometrist will use the retinoscope to shine light into each of your eyes in turn so they can observe the reflection of the light passing through your eye and onto the retina (the lining at the back of your eye).
The optometrist will turn the retinoscope from side to side, which causes the light patch reflected by your retina to move. By doing this, the optometrist can estimate from the direction and speed that the light appears to move whether you are short-sighted or long-sighted and by how much. From that, they’ll be able to judge whether your eyesight could be improved by wearing glasses or updating the strength of your current glasses if you already wear them.
To confirm what type of vision correction you will need, and how strong it needs to be (your prescription), your optometrist will then place different lenses in front of your eye until the reflected light appears still, even when the retinoscope is moved. A simple calculation then determines your prescription. Your optometrist will be able to explain any part of the retinoscopy if you have questions.
Are dilating eye drops necessary for retinoscopy?
The retinoscopy will be conducted in a darkened room, so your pupils will dilate automatically. It’s unlikely that you’ll need to have any eye drops to dilate your pupils, but if you do, it’s important to note that you wouldn’t be able to drive immediately after, until the effects have worn off.
For younger children, drops are sometimes required to relax certain structures of the eye, like the pupil. This is because children can change the focus of their eyes so quickly and readily, making retinoscopy less accurate. Using the drops enables a more accurate reading from retinoscopy which is vital in cases where there is a suspicion of amblyopia or lazy eye<.