The small, fleshy structure located in the inner corner of the eye, closest to the nose, is called the lacrimal caruncle. This mound of tissue sits at the medial canthus, the point where the upper and lower eyelids meet. Although often overlooked, the caruncle is a normal anatomical feature that helps maintain the health of the eye’s surface. Understanding its composition and function can demystify this part of the ocular anatomy.
Defining the Caruncle and Plica Semilunaris
The lacrimal caruncle is a conical, reddish-pink nodule distinguished by tissue that resembles skin more than the adjacent conjunctiva. Unlike the eye’s mucous membrane, the caruncle contains sebaceous (oil) glands, sudoriferous (sweat) glands, and sometimes fine, colorless hairs. These components are responsible for the whitish, sometimes crusty, secretion that often collects in the inner corner of the eye after sleep.
The caruncle is situated directly beside the plica semilunaris, a crescent-shaped fold of the conjunctiva. The plica semilunaris is a loose fold considered a vestigial remnant of the “third eyelid” (nictitating membrane) found in many animals. The caruncle and the plica work together in the medial canthus to support tear dynamics and eye movement. The plica’s looseness allows the eyeball to rotate fully toward the nose without restricting motion.
Biological Function
The caruncle’s primary functional role is contributing to the stability and quality of the tear film coating the eye’s surface. The sebaceous and sweat glands release oily and mucous secretions that mix with tears. This mixture helps maintain the tear film’s composition, particularly the outer lipid layer, which slows the evaporation of the watery tear layer.
Beyond tear film maintenance, the caruncle acts as a protective barrier and collection point. Its elevated position helps channel tears and debris toward the lacrimal puncta, the small openings leading to the tear drainage system. Particles flushed from the eye surface collect on the caruncle before being drained, supporting ocular cleanliness. The lymphoid tissue in the adjacent plica semilunaris also suggests a role in local immune response and protection against allergens and pathogens.
Common Causes of Irritation and Changes
The caruncle’s complex structure and exposed location make it susceptible to irritation and visible changes. A common cause of swelling and redness is allergic conjunctivitis, where the tissue reacts to airborne allergens. This inflammatory response is triggered by histamine release, causing the caruncle and plica to become inflamed and sometimes itchy.
Irritation can also result from a foreign body or chronic dry eye, leading to inflammation. Since the caruncle contains oil and sweat glands, gland blockage is a frequent issue, similar to a pimple forming on the skin. When these glands become clogged, they can cause localized tenderness and swelling.
Changes in the caruncle’s appearance may also be due to common, non-emergency growths. These include retention cysts, which form when a duct becomes blocked and fluid accumulates. Other benign lesions, such as nevi (moles) or papillomas (wart-like growths), can also develop, often appearing as a small, slightly raised area with an altered color or texture. While most lesions are benign, any sudden or noticeable change in size or color warrants professional evaluation.
When to Seek Professional Care
Most minor irritation, such as redness or mild swelling due to allergies or temporary dryness, will resolve with basic self-care, like warm compresses or over-the-counter eye drops. However, certain symptoms should prompt a visit to an eye care professional. Immediate consultation is advised for persistent or worsening pain, especially if the caruncle is tender to the touch or swelling rapidly increases.
Any change in vision, the presence of a new, quickly growing mass, or bleeding from the caruncle are serious signs requiring prompt medical attention. If a mass exhibits an atypical appearance, such as irregular borders or a change in color, a doctor needs to rule out more serious conditions. Additionally, if discomfort or swelling does not resolve within 48 to 72 hours, a professional examination is necessary to diagnose and treat a potential infection or underlying systemic issue.