The common phenomenon of waking up with “sleep” in the eyes, often called “eye boogers,” is a natural biological process that keeps the ocular surface clean. This substance, medically termed rheum or gound, is a protective mechanism designed to collect and remove waste products from the eye. Rheum is an accumulation of various substances produced continuously, becoming noticeable only when they are not regularly flushed away. Its presence is a normal sign that the eye’s self-cleaning system is functioning properly.
The Basic Components of Rheum
Rheum is composed of several distinct biological materials that form the eye’s protective layer. A primary component is mucin, a thin, watery mucus secreted by the goblet cells in the conjunctiva (the clear membrane covering the white of the eye and inner eyelid). Mucin traps foreign particles and debris, acting as a sticky net.
Another part is meibum, an oil from the meibomian glands along the rim of the eyelids. This oily substance forms the outermost layer of the tear film, preventing evaporation and keeping the eyes lubricated. Mixed into this matrix are shed epithelial cells from the eyelids and cornea, environmental contaminants like dust and pollen, and a small amount of water-based tears that help suspend these components.
The Process of Formation
The difference between having nearly invisible discharge and waking up with crusty rheum lies in the action of blinking. Throughout the day, the involuntary blink reflex occurs frequently (typically 15 to 20 times per minute). Each blink spreads the tear film evenly across the eye, washing the accumulating mucus, oil, and debris toward the tear ducts near the nose.
During sleep, the eyes are closed, and blinking ceases. Tear production also slows down, meaning the mixture of mucus, oil, and debris is no longer actively drained. This allows the material to gather in the corners of the eye and along the lash line. As the water content evaporates overnight, the remaining concentrated substance dries out and solidifies into the familiar crusty texture.
Signs of Abnormal Discharge
While a small amount of pale or clear crust upon waking is normal, a change in the quantity or quality of the discharge can signal a health issue. Normal rheum is typically whitish or clear and dry, easily wiping away. Discharge that is suddenly excessive, thick, or sticky suggests an inflammatory response.
A warning sign is a change in color, particularly if the discharge is yellow, green, or gray. This discoloration often indicates pus, which is a collection of white blood cells fighting a bacterial infection, such as bacterial conjunctivitis (“pink eye”). Abnormal discharge may also be accompanied by symptoms like persistent redness, eye pain, blurry vision, or sensitivity to light. If these abnormal signs persist, especially if the eyelids are stuck together, seeking medical advice is recommended.