If you have astigmatism like almost half of the world’s population, then you will know what we mean when we reference a fuzziness or halo. If you don’t have astigmatism, here’s a quick 101.
The “normal” eye has a cornea and lens that are smooth and rounded in shape. This allows for light to pass through the eye in focused rays creating a sharp picture.
When you have astigmatism, your eye is not perfectly smooth or rounded and that means that light does not pass through the eye in a focused ray. This causes things to look blurry or “fuzzy” when they are close to the eye and far from it.
Now, when certain colors are combined – bright colors on a dark background, for example, white text on a black background, something called “halation” occurs. This is when something appears to have a fuzzy “halo” around it. So combine this natural halation effect with someone who already sees a fuzziness around objects because they have astigmatism and you have text that is very difficult to read.
Since almost half of the world’s population has astigmatism, it’s prudent to keep this in mind when coming up with design themes.