Waking up with a small, crusty accumulation in the corner of the eyes, commonly referred to as “sleep” or “eye gunk,” is normal. This morning matter is medically known as rheum, and its presence is a normal indicator of a healthy, functioning ocular system. The eye is constantly performing a cleaning process, and rheum is the visible result of this protective maintenance. Understanding what this material is and why it appears only upon waking explains its role in maintaining eye health.
The Composition of Eye Discharge
The substance that forms eye rheum is a dried mixture of the components that make up the eye’s tear film. The tear film is a three-layered coating that lubricates the eye and protects the cornea from damage and foreign particles. Its primary ingredients are water, mucus, and oil.
Mucus (mucin) is produced by the conjunctiva and helps spread the tear film evenly across the eye’s surface. Oil (meibum) is secreted by the meibomian glands along the eyelid margins, preventing the watery layer from evaporating too quickly. These secretions combine with discarded epithelial cells and microscopic debris like dust caught throughout the day, forming the eye discharge.
Why Accumulation Happens During Sleep
The reason rheum accumulates and dries into a crust is directly related to the absence of blinking while asleep. During the day, the eyelids blink approximately 10 to 20 times per minute, acting like windshield wipers. This action constantly washes the tear film and collected debris into the nasolacrimal ducts, which drain into the nose, keeping the eye surface clear.
When the eyes are closed during sleep, this flushing mechanism stops. Protective secretions and trapped particles continue to be produced but are no longer being drained away. They gather in the inner corner of the eye, where they are concentrated by the warmth of the eyelid. As the watery portion of the tear film evaporates overnight, the remaining mucus, oil, and cellular material dry out, forming the crusty or sticky substance observed upon waking.
When Sleep Crust Signals a Health Issue
Normal rheum is usually dry, small, and white or a pale cream color; it is easily wiped away and does not interfere with vision. However, a significant increase in the amount or a change in the color and consistency of eye discharge can indicate a health problem, such as an infection or inflammation.
Discharge that appears thick, yellow, or green often suggests a bacterial infection, such as bacterial conjunctivitis (“pink eye”). This type of discharge is frequently pus-like and can be so sticky that it glues the eyelids shut. Viral infections typically produce discharge that is clear, watery, and less viscous, though it may contain a slight white or light yellow mucus.
Signs of Abnormal Discharge
Other signs that the discharge is abnormal include an amount so excessive it reappears shortly after wiping. It may also be accompanied by persistent symptoms like eye pain, increased light sensitivity, or blurred vision.
Conditions such as dry eye, allergic conjunctivitis, or blepharitis (inflammation of the eyelid margins) can also cause increased or foamy discharge. Any change in discharge combined with pain or vision changes warrants an evaluation by an eye care professional.