H Locke, a UX designer, talks about astigmatism, which affects around 47% of the UK population. Actually Locke points out it affects most of the population, but the 47% figure is those that require corrective treatment, such as lenses or glasses.
The condition affects the shape of the eye, making it more ‘rugby ball’ shaped than football shaped. This leads to light being focused at more than one place in the eye, and can cause blurred vision, headaches and eye strain.
Locke says that the ‘dark mode’ on certain websites can cause an effect called ‘halation’, for those with astigmatism. There’s a mocked up screenshot in the article, demonstrating the effect, but it essentially makes the area surrounding highlights blurry. In dark mode, there are a lot of highlights (e.g. white images are more pronounced), so the text around the images becomes blurred.
Dark mode advocates often cite it as an accessibility feature – and it is an improvement for some people – but Locke reminds us of the importance of making such modes optional.
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