IT IS a drug that has made a lot of people very happy, but ironically it might also have made their outlook rather blue.

Men taking high doses of Viagra report seeing a blue haze, but until now nobody has studied whether normal doses of the drug affect vision. And since most people turn off the lights after taking Viagra, such side effects are likely to be under-reported.

Glen Jeffery, at the UK’s Institute of Ophthalmology in London and four of his colleagues decided to investigate – all in the name of science, of course – and took a standard 100-milligram dose of Viagra. “A little …