The small, pink structure tucked into the inner corner of your eye is part of the visual system’s intricate design. This fleshy corner, known as the medial canthus, houses specialized tissues that protect the eye’s surface and manage tear flow. It is an anatomical junction where skin, conjunctiva, and tear ducts meet.
Identifying the Lacrimal Caruncle and Plica Semilunaris
The pink structure involves two distinct, closely associated anatomical features. The most prominent part is the small, fleshy mound called the lacrimal caruncle. This nodule sits at the inner corner of the eye, where the upper and lower eyelids meet.
The lacrimal caruncle contains elements typically found on the skin, such as fine hairs, sebaceous glands, and sweat glands. Immediately adjacent to the caruncle is the plica semilunaris, a small, crescent-shaped fold of thin, moist tissue. This fold is part of the conjunctiva, the transparent membrane covering the white part of the eye.
Function and Evolutionary Context
The tissues in the medial canthus function to support the tear film and eye movement. The lacrimal caruncle’s sebaceous and sweat glands secrete oils and mucus that contribute to the outer layer of the tear film. This oily layer reduces tear evaporation and stabilizes the film across the eye’s surface.
The caruncle also acts as a small barrier, collecting foreign debris swept toward the inner corner during blinking. The adjacent plica semilunaris provides necessary slack in the conjunctiva, permitting free rotation and movement of the eyeball toward the nose. Without this fold, the conjunctiva would restrict full movement of the globe.
The plica semilunaris is considered a vestigial remnant of the nictitating membrane. This “third eyelid” is a transparent lid found in many animals, including birds, reptiles, and some mammals. While the functional membrane rapidly sweeps across the eye for protection and moistening, in humans, it has been reduced to a non-functional fold of tissue.
Common Causes of Irritation and Changes
Because the caruncle contains glands and skin-like tissue, it is susceptible to inflammation and common growths. Redness, itching, and swelling of the caruncle and plica semilunaris frequently occur during ocular allergies or infectious conjunctivitis. These reactions are typically transient and resolve once the underlying irritation or infection is addressed.
A common issue is the development of a pinguecula, a yellowish-white, slightly raised mass of protein, fat, and calcium that often appears on the conjunctiva near the nasal side. While the pinguecula is benign, it can become inflamed (pingueculitis), causing redness, irritation, and a gritty sensation. Other benign growths that may occur directly on the caruncle include nevi (moles) or papillomas.
Inflammation of the caruncle, termed carunculitis, can occur if the sebaceous glands become blocked or infected. Persistent swelling, tenderness, or a noticeable discharge may also indicate an infection of the nearby tear drainage channels, known as canaliculitis. Any persistent or concerning changes in the appearance of the inner corner of the eye warrant consultation with an eye care professional.