The human eye is a complex organ, and the area commonly known as the “inner corner” often prompts questions about its proper anatomical name. Though frequently overlooked, this small region plays a role in the eye’s function and protection.
The Medical Term
The inner corner of the eye is medically known as the medial canthus. The word “canthus” originates from the Greek word “kanthos,” meaning “corner of the eye.”
The descriptor “medial” indicates its position closer to the center of the face, near the nose. This differentiates it from the “lateral canthus,” the outer corner of the eye, situated closer to the temple.
Anatomy and Function
Within the medial canthus lies a small, fleshy bump known as the lacrimal caruncle. This structure is composed of modified skin containing sebaceous (oil) and sweat glands. The caruncle collects debris, such as dust or dried tears, and its secretions contribute to the tear film, helping to lubricate the eye.
Adjacent to the caruncle is a small, crescent-shaped fold of tissue called the plica semilunaris. This structure is considered a vestigial remnant of the nictitating membrane, or “third eyelid,” found in many other animals. While its functional role in humans is minimal, it may aid in tear drainage and allow for greater eye rotation.
The medial canthus is also home to the lacrimal puncta, tiny openings on the inner edge of both the upper and lower eyelids. These puncta serve as the entry points for tear drainage. Every blink helps to pump tears into these openings.
From the lacrimal puncta, tears enter small channels called the lacrimal canaliculi, which lead into the lacrimal sac. The lacrimal sac, a small reservoir within the medial canthus, collects tears before they drain further. Tears then pass from the lacrimal sac into the nasolacrimal duct, which carries them into the nasal cavity. This intricate system ensures the efficient drainage of excess tears, maintaining a healthy and protected eye surface.
Common Issues
One common issue affecting the medial canthus is a blocked tear duct, medically termed nasolacrimal duct obstruction. When this drainage pathway becomes blocked, tears cannot drain properly, leading to excessive tearing, also known as epiphora. This condition can also result in discharge and is frequently observed in infants.
The lacrimal caruncle and surrounding area can accumulate mucus and dried tear film, particularly noticeable upon waking. This results in the “crusty eyes” or “sleep” often found in the inner corner. While often benign, persistent or excessive discharge may indicate an underlying issue.
Infections of the lacrimal sac, known as dacryocystitis, can occur in the medial canthus. This condition typically presents with pain, redness, and swelling near the inner corner of the eye. Pus or discharge may also be present, and in some cases, a fever can develop.
Another characteristic associated with the medial canthus is the presence of epicanthal folds. These are skin folds of the upper eyelid that cover the inner corner of the eye. Epicanthal folds are a normal anatomical variation, commonly observed in individuals of East Asian descent and in young children of various ethnicities before the nasal bridge fully develops. If any persistent or concerning symptoms arise in the medial canthus area, it is advisable to consult a healthcare professional for proper evaluation.