Wiping away the small collection of crusty or sticky material found in the corners of the eyes is a common morning ritual. This phenomenon, widely called “sleep in the eyes” or “eye gunk,” is medically known as rheum or gound. Experiencing a small amount of this discharge is a universal part of healthy eye function, indicating the eye’s natural cleansing process is working. Understanding the science behind its formation helps distinguish a normal occurrence from a potential health concern.
The Science Behind Sleep Crust Formation
Sleep crust, or rheum, is the accumulated debris from the tear film that covers the eye’s surface. It is a mixture primarily composed of mucus from the conjunctiva and meibum, an oily substance secreted by glands in the eyelids. The rheum also contains exfoliated skin cells, dust, and other environmental particles collected during the day.
During waking hours, the continuous action of blinking (about 15 to 20 times per minute) constantly flushes this mixture away. Tears carry the debris toward the tear ducts, known as the lacrimal puncta, where it drains into the nasal cavity, preventing the debris from hardening or collecting. When a person is asleep, blinking stops and tear drainage is significantly reduced. This allows the debris-filled tear film to pool at the inner corners of the eyes. As the watery component evaporates overnight, the remaining non-liquid substances dry out and form the characteristic crusty residue.
Normal Versus Abnormal Eye Discharge
A small amount of morning rheum is a sign of a healthy, functioning eye, but changes in its appearance or volume can signal an underlying issue. Normal sleep crust is typically dry, crusty, and located at the inner corner of the eye. Its color is usually clear, white, or a pale cream, and it is easily wiped away.
Discharge is considered abnormal if there is a significant increase in volume, a sticky consistency, or a change in color. Excessive discharge may glue the eyelids together or be accompanied by symptoms such as redness, swelling, light sensitivity, or pain. Discharge that is thick, goopy, and takes on a yellow, green, or grayish color suggests an immune response, indicating the eye is actively fighting an infection or reacting to severe irritation.
Common Causes of Excessive Discharge
When discharge is excessive or changes color, it often points to inflammatory or infectious conditions of the eye. Conjunctivitis (pink eye) is a frequent culprit, causing inflammation of the clear membrane lining the eye. Viral conjunctivitis typically produces a watery or sticky white discharge, while bacterial infection results in a thicker, pus-like discharge that is often yellow or green.
Blepharitis, an inflammation of the eyelid margins, leads to persistent crusty buildup at the base of the eyelashes, often causing foamy or oily discharge due to clogged oil glands. Dry eye syndrome can paradoxically cause a stringy, mucoid discharge as the eye attempts to compensate for inadequate lubrication.
Tear duct blockages also cause excessive discharge because tears and mucus cannot drain properly. In adults, this causes tears and debris to back up onto the eye’s surface, often leading to a sticky, gooey, yellow discharge. If abnormal symptoms like colored discharge, pain, or blurred vision persist, consulting a medical professional is necessary to identify the cause and prevent complications.