Myopia is partly down to genes. But if so, how has it survived evolutionary pressures? Any hunter-gather with poor vision would not have survived long in the hostile Palaeolithic age.

Researchers at Queen Mary Hospital and the University of Hong Kong found that the genes involved in myopia survived because they have a role in intelligence. The idea is that intelligence and myopia go together because the growth of both the brain and the eyes has a common genetic base. Crucially, the genes responsible for myopia have to be turned on by an environmental trigger. In the distant past, that trigger was not around, so our ancestors benefited from superior intelligence, but did not have the handicap of being short-sighted .

And the environmental trigger? Well, hunter-gathers never read; it may be reading, especially when young, may be the trigger.