6 in a list of "10 ideas that shouldn’t have worked – but made millions" by MSN Money,[1] and by 2004, were being sold in 4,500 shops in 16 countries[4] and now include the option of prescription lenses.

[5] The British newspaper Metro reported in March 2007 the story of a dog suffering from a rare autoimmune disorder which means its eyes cannot produce tears.

Veterinarian Pete Wedderburn reported in his Daily Telegraph blog in 2009 the case of a terrier that suffered from an ophthalmological condition in which tiny specks of debris were floating around inside its eyes.

When exposed to bright sunshine, the dog would twist to its side while snarling and yelping; something that was originally thought to be the exacerbation of an existing arthritis condition.

Eventually the owner found that a baseball cap designed for dogs proved to be the solution as the terrier did not mind wearing it.