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]
Visual perception The visual system in animals allows individuals to assimilate information from their surroundings. The act of seeing starts when the cornea and then the lens of the eye focuses light from its surroundings onto a light-sensitive membrane in the back of the eye, called the retina. The retina is actually part of the brain that is isolated to serve as a transducer for the conversion of light into neuronal signals. Based on feedback from the visual system, the lens of the eye adjusts its thickness to focus light on the photoreceptive cells of the retina, also known as the rods and cones, which detect the photons of light and respond by producing neural impulses. These signals are processed via complex feedforward and feedback processes by different parts of the brain, from the retina upstream to central ganglia in the brain.