The small, fleshy mass in the inner corner of the eye, near the tear duct opening, is a normal part of human eye anatomy. The structure is located in the section of the eye closest to the nose, known as the medial canthus. This subtle feature is present in everyone and plays a functional role in maintaining eye comfort and tear flow.
Identifying the Lacrimal Caruncle
The structure is called the caruncula lacrimalis, or simply the lacrimal caruncle. It presents as a small, pink or reddish nodule situated in the medial corner of the eye. Its appearance is different from the surrounding tissue because it is covered in modified skin, not the transparent membrane of the conjunctiva.
The caruncle contains various specialized elements, including sebaceous (oil) glands and sweat glands, and they are sometimes accompanied by fine, soft hairs. This composition distinguishes the caruncle and explains its fleshy, skin-like texture compared to the smooth, wet surface of the eyeball. The entire structure resides adjacent to the tiny openings, called puncta, which are the start of the tear drainage system.
Its Current Role in Eye Health
The lacrimal caruncle contributes to the eye’s continuous self-maintenance process. The sebaceous glands within the caruncle secrete a thin, oily substance called sebum. This oily layer mixes with the aqueous component of tears to form the complete tear film, helping to prevent the rapid evaporation of moisture from the eye’s surface.
The caruncle also works with the tear drainage apparatus. Tears naturally pool in the inner corner of the eye, in an area called the lacrimal lake, before draining through the puncta. The caruncle helps guide the collected tears and small particles of debris toward these drainage openings. This action ensures the tear film remains stable and that foreign matter is efficiently washed away.
Evolutionary Context: The Third Eyelid Remnant
The caruncle’s location is understood by considering the crescent-shaped fold of tissue immediately next to it. This fold is known as the plica semilunaris, and both structures are considered evolutionary remnants. They are the vestigial remains of the nictitating membrane, or “third eyelid.”
The nictitating membrane is fully functional in a wide range of other animals, including birds, reptiles, and many mammals like cats and sharks. In humans, the caruncle and the plica semilunaris are the non-functional echoes of this more extensive protective mechanism. Our upper and lower eyelids provide sufficient protection, but the remaining vestigial tissue connects us to our evolutionary history.
Common Causes of Irritation
The caruncle is susceptible to irritations and infections. One common issue is localized inflammation, which can be triggered by environmental factors such as pollen, dust, or residual makeup, leading to redness and swelling.
Allergies are a frequent cause of irritation, where the release of histamine can make the caruncle and the adjacent fold itchy and visibly inflamed. Furthermore, the area is the site of accumulation for the mixture of mucus, oil, and shed skin cells that form “sleep” or “crust” in the morning. This debris accumulation can sometimes cause temporary blockage or mild discomfort.
More serious inflammation can be a sign of infection, such as bacterial or viral conjunctivitis, causing significant redness and swelling. Infections like dacryocystitis (of the tear drainage system) or canaliculitis (of the tear ducts) may also present with swelling and tenderness near the caruncle area. If the swelling is accompanied by persistent pain, changes in vision, or a thick discharge, consult with an eye care professional for proper diagnosis and treatment.