A lot of people are short-sighted - have myopia. The prevalence in western countries is 30-40% and in asian countries as high as 80%. This is weird: evolution should have removed anything genetic which cause so lethal a disability.
This suggests we look at environmental causes. This scary paper, An Evolutionary Analysis of the Etiology and Pathogenesis of Juvenile-Onset Myopia, uses data on hunter-gatherer societies which were westernised within the last hundred years to show that myopia went from near-zero to western levels in one or two generations. The cause? Not so much 'near work' (reading, writing and computer screens) as changes in diet.
The culprit is sugar, and in particular processed carbohydrates with a high glycemic load. Read the paper for the details but along with obesity and diabetes, we can now add short-sightedness to the ills of junk food.