After seeing Sherlock writer Mark Gatiss’s ‘Sleep No More’ episode of Doctor Who last season, did you wonder what the ‘sleep’ in your eyes actually is?

Unfortunately it’s not really the Sandmen from Le Verrier Space Station.

The clever folks at todayifoundout.com explain that the “sleep” is in fact a type of “rheum”, known as “gound”.

The trivia website writes: “Gound is made up of a mixture of dust, blood cells, skin cells, etc. mixed with mucus secreted by the conjunctiva, as well as an oily substance from the meibomian glands.

“The meibomian glands are a type of sebaceous gland that line the rim of the eyelids with about fifty on the top and twenty five on the bottom of each eye. They secrete an oily substance called meibum that performs a variety of functions including: helps seal your eyes in an air tight fashion when they are closed; prevents tears from spilling onto your cheeks; and helps keep tears that coat your eyes from evaporating. It is this oily substance that is one of the primary components in gound, mixed with mucin from the conjunctiva and various foreign particles in your eye.”

> Read their full blog post here.

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