High illumination levels may protect against myopia

This experimental study involving chicks suggests that the apparent protective effect against myopia afforded to children who spend more time outdoors can be explained, at least in part, by exposure to higher ambient illumination.
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The study's authors concluded that it is not necessarily the type of illumination - natural or unnatural - that matters in the protection against the development of myopia but rather the intensity of illumination, although it is still unclear exactly how illumination does this.

From Investigative Ophthalmology & Visual Science