Could an internet “illusion” actually be useful?

April 11, 2016

Red circle for eye test

Have you been caught up in the rush to test your vision with the red dot? In the best viral vision check we’ve seen for a while, this red dot contains an image that tests your sensitivity to contrast.

When you read print, or look at a standard eye exam chart, the text is usually black on white, the highest contrast you can get, so it gives you the best result. However, as the contrast decreases, things are more difficult to see. Imagine writing printed in light grey on white, or different shades of brown and beige; not so easy to see now? This reduction in contrast is what happens when you try to see in low light, or fog, or glare. So even if you have 20/20 vision in an eye exam, you will still find night driving more difficult if your contrast sensitivity is poor. You may have seen yellow tinted lenses for night driving, these are designed to improve the contrast of what you see, and will help some people.

Reduced contrast sensitivity can affect all visual tasks, including driving, reading, and watching television, and can make you more likely to fall on stairs as the edge of one step isn’t obvious against the colour of the one below. Just like your high contrast visual acuity, contrast sensitivity can vary from one normal person to another, but can also be affected by eye conditions such as cataract, glaucoma, or diabetic eye disease. It can also be affected by laser refractive surgery, and is one of the reasons that if you have had surgery to correct your prescription, your night vision may still not be as good as you remember it was before.

In the image above, the red circle contains an image in a colour of low contrast to the surrounding red dot. Some people see nothing at all, others see an outline, and some see more detail.

The image is described and shown in the article linked below, so I won’t spoil it until you’ve had a go!

If you can’t see anything in the red dot, there might still be nothing at all wrong with your eyes, but if you haven’t had an eye exam for a while, book in for one anyway to make sure.

Here’s an article with more detail, and pictures of the image hidden in the red dot:

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