Finding a small amount of white or clear material collected in the corner of your eyes upon waking is a universal, everyday experience. This material is a natural byproduct of your eye’s constant self-cleaning process. While most people casually refer to it as “sleepers,” “eye gunk,” or “sleep sand,” it has a formal scientific designation. Understanding this substance involves recognizing it as part of the eye’s protective tear film system. The presence of this material is a sign that your eyes were actively maintaining their surface health throughout the night, keeping the delicate ocular surface clear of debris and waste.
The Scientific Name and Composition
The technical term for the material that collects in the corners of the eyes is rheum, sometimes referred to by ophthalmologists as gound. This substance is a complex mixture of components constantly produced to maintain a healthy ocular surface. Rheum is primarily composed of mucus, oils, dead skin cells, and various forms of environmental debris.
The mucus component, known as mucin, is secreted by specialized goblet cells within the conjunctiva. Mucin is highly hydrated and helps anchor the watery layer of the tear film to the surface of the cornea. The oily part of the mixture, called meibum, comes from the meibomian glands embedded in the eyelids. This lipid-rich secretion forms the outermost layer of the tear film, acting like a protective seal to slow the evaporation of the underlying watery layer.
Rheum also contains exfoliated epithelial cells and microscopic dust particles. The final consistency, whether sticky and wet or dry and crusty, depends on the degree to which the water and salts from the aqueous portion of the tears have evaporated. The formation of rheum is a necessary mechanism for clearing the ocular surface of waste products.
Why They Accumulate During Sleep
The natural buildup of rheum is a direct consequence of the change in tear film dynamics that occurs when the eyes are closed during sleep. While a person is awake, the act of blinking is a continuous, sweeping motion that redistributes the tear film across the eye and directs debris toward the small drainage channels near the nose, called the nasolacrimal ducts. This constant mechanical action prevents any significant accumulation of material.
When the eyelids are closed, this sweeping action ceases entirely, allowing the components of the tear film to pool in the inner corner of the eye. The material concentrates in this area because the eyelids, while closed, still allow some tear drainage toward the puncta, the tiny openings that lead into the nasolacrimal system. Since the eyelids are not actively pushing the material into the ducts, the debris settles, and the water content of the tears begins to evaporate. This process of settling and evaporation results in the semi-solid, often crusty material found upon waking.
When to See a Doctor
While small amounts of clear or whitish rheum are a normal sign of eye health, significant changes in the amount, color, or consistency of the discharge can indicate a medical issue that requires professional attention.
Excessive Discharge and Color
A major warning sign is an excessive volume of discharge that makes the eyelids feel glued shut in the morning or persists throughout the day. This copious, sticky mattering often suggests a bacterial infection, such as bacterial conjunctivitis.
The color of the discharge is a reliable indicator of potential pathology; normal rheum is typically clear, white, or light cream. Discharge that appears yellow, green, or gray often signifies the presence of white blood cells and pus, which strongly suggests an active bacterial or viral infection. A stringy, white, or watery discharge can sometimes be associated with allergic conjunctivitis or chronic conditions like dry eye or blepharitis.
Accompanying Symptoms
A doctor should also be consulted if the eye crustiness is accompanied by other distressing symptoms. These co-occurring symptoms suggest the underlying cause is more than simple overnight accumulation and may be a sign of a condition like a blocked tear duct, a severe infection, or significant inflammation.
- Noticeable redness of the eye.
- Persistent pain.
- Eyelid swelling.
- Increased sensitivity to light.
- A gritty feeling that does not resolve after gently cleaning the eye.