where does the crust in your eyes come from
Rheum Rheum (/ˈruːm/; from Greek: ῥεῦμα rheuma "a flowing, rheum"), also known as gound, is thin mucus naturally discharged from the eyes, nose, or mouth during sleep (cf. mucopurulent discharge).[1][2][3] Rheum dries and gathers as a crust in the corners of the eyes or the mouth, on the eyelids, or under the nose.[3] It is formed by a combination of mucus (in the case of the eyes, consisting of mucin discharged from the cornea or the conjunctiva), nasal mucus, blood cells, skin cells, or dust. Rheum from the eyes is particularly common. Dried rheum is commonly called sleep,[4] sleepy-seeds,[5] sleepy buds,[5] sleepy sand, eye goop, cheese, or sleepy dust.[6]
Sclera The sclera,[help 1] also known as the white of the eye, is the opaque, fibrous, protective, outer layer of the human eye containing mainly collagen and some elastic fiber.[2] In humans, the whole sclera is white, contrasting with the coloured iris, but in other mammals the visible part of the sclera matches the colour of the iris, so the white part does not normally show. In the development of the embryo, the sclera is derived from the neural crest.[3] In children, it is thinner and shows some of the underlying pigment, appearing slightly blue. In the elderly, fatty deposits on the sclera can make it appear slightly yellow. Many people with dark skin have naturally darkened sclerae, the result of melanin pigmentation.