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Rheum from a cat's eyes. Rheum ( / ruːm /; from Greek: ῥεῦμα rheuma 'a flowing, rheum') is a thin mucus naturally discharged from the eyes, nose, or mouth, often during sleep (contrast with 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 ...
The night hag or old hag is the name given to a supernatural creature, commonly associated with the phenomenon of sleep paralysis. It is a phenomenon in which the sleeper feels the presence of a supernatural, malevolent being which immobilizes the person as if sitting on their chest or the foot of their bed. The word "night-mare" or "nightmare ...
Blue light, a type of high-energy light, is part of the visible light spectrum. High-energy visible light (HEV light) is short-wave light in the violet/blue band from 400 to 450 nm in the visible spectrum, which has a number of purported negative biological effects, namely on circadian rhythm and retinal health (blue-light hazard), which can lead to age-related macular degeneration.
Phosphene. An artist's representation of how some people may see phosphenes by retinal stimulation. A phosphene is the phenomenon of seeing light without light entering the eye. The word phosphene comes from the Greek words phos (light) and phainein (to show).
Lagophthalmos. Lagophthalmos is the inability to close the eyelids completely. [ 1] Blinking covers the eye with a thin layer of tear fluid, thereby promoting a moist environment necessary for the cells of the exterior part of the eye. The tears also flush out foreign bodies and wash them away.
Entoptic phenomena (from Ancient Greek ἐντός (entós) 'within' and ὀπτικός (optikós) 'visual') are visual effects whose source is within the human eye itself. (Occasionally, these are called entopic phenomena, which is probably a typographical mistake.) In Helmholtz 's words: "Under suitable conditions light falling on the eye ...
Rapid eye movement sleep ( REM sleep or REMS) is a unique phase of sleep in mammals (including humans) and birds, characterized by random rapid movement of the eyes, accompanied by low muscle tone throughout the body, and the propensity of the sleeper to dream vividly. The REM phase is also known as paradoxical sleep ( PS) and sometimes ...
Specialty. Psychiatry. Rhythmic movement disorder ( RMD) is a neurological disorder characterized by repetitive movements of large muscle groups immediately before and during sleep often involving the head and neck. It was independently described first in 1905 by Zappert as jactatio capitis nocturna and by Cruchet as rhythmie du sommeil. [ 1]