Bookmark: "Accessibility for People with Astigmatism"

Sebastian Greger


While high contrast is important for accessibility, this article is a good reminder why overdoing it is not a good idea:

There is a myth about white text over black backgrounds being the best color contrast combination for accessibility, but in reality, white text on black backgrounds creates a visual fuzzing effect for people with astigmatism called “halation”.

The fuzzing effect of “halation” may impact up to half of the population, leading to difficulty reading and potentially headaches etc. when white text is placed on a black background.

It’s actually quite astonishing that this “extreme contrast issue” is not a WCAG criterion itself:

Automated contrast-ratio checkers would not detect a problem or any WCAG success criteria failures using this combination of colors, but it will impact end-users. This is another reason why manual testing is still a key component of accessibility testing.

On a related note: this is particularly relevant when designing for the popular “dark mode”.