The medial canthus is the inner corner of the eye where the upper and lower eyelids meet nearest the nose. Problems here, such as pain or swelling, can cause discomfort due to the area’s proximity to the eye. Understanding why the right medial canthus might be affected involves recognizing the structures within this small space. This inner corner serves as a central hub for the tear drainage system, making it vulnerable to blockages and infections.
Anatomy of the Medial Canthus
The location of the medial canthus is defined by the convergence of the eyelids near the bridge of the nose. This area contains the lacrimal drainage system, which collects and removes tears from the eye’s surface. The process begins with the puncta, two tiny openings—one on the margin of the upper lid and one on the lower lid—located near the canthus.
Tears enter the puncta and pass into the canaliculi, small channels that join to form a common channel that empties into the lacrimal sac. The lacrimal sac is a small reservoir that sits within a bony depression on the side of the nose.
From the lacrimal sac, tears drain downward through the nasolacrimal duct, which empties into the nasal cavity. If any part of this pathway becomes compromised, tears can stagnate. This stagnation often leads to pain and swelling that manifests directly over the lacrimal sac beneath the medial canthal tendon.
Inflammatory Issues of the Tear Drainage System
The most frequent cause of pain and swelling in this region is dacryocystitis, an infection and inflammation of the lacrimal sac. This condition usually begins when the nasolacrimal duct, the final drainage pathway, becomes blocked, causing tears to back up and stagnate within the lacrimal sac. This stagnant fluid creates an environment for bacteria, such as Staphylococcus or Streptococcus species, to proliferate and cause an acute infection.
Acute dacryocystitis presents with a sudden onset of severe pain, marked redness, and a tender, firm swelling localized to the inner corner of the right eye, near the bridge of the nose. Pressure applied to the swollen area may cause a mucopurulent discharge to be expressed through the puncta. When the blockage is less complete or the infection is milder, the condition may become chronic dacryocystitis, which primarily causes persistent excessive tearing (epiphora) and sometimes a mild discharge, with less pronounced pain or swelling.
Obstruction can also occur earlier in the tear pathway, such as at the level of the puncta or canaliculi. Punctal stenosis, or the narrowing of the punctal opening, restricts tear entry into the system and contributes to tear stasis. Inflammation of the canaliculi, known as canaliculitis, can lead to localized pain and swelling directly over the channel, often accompanied by a characteristic yellow or white discharge due to the presence of bacterial concretions.
Structural and Dermatological Concerns
Causes of medial canthus swelling not related to the tear drainage system often involve the surrounding skin and soft tissue. This area is susceptible to dermatological conditions, including benign growths such as sebaceous cysts or papillomas, which may cause localized swelling and tenderness.
A more serious concern involves skin malignancies, particularly Basal Cell Carcinoma (BCC), the most common form of cancer affecting the eyelids. The medial canthus is a frequent site for BCC, second only to the lower eyelid. These lesions often appear as a slowly enlarging, reddish nodule with a pearly border and sometimes a central ulceration.
BCCs in the medial canthus can be deeply invasive, potentially growing into the eye orbit, sinuses, or surrounding bone. Trauma, such as a direct blow or a facial fracture involving the nasal bones, can also cause acute swelling and pain by disrupting the bony structure that houses the lacrimal sac. Injury to the medial canthal tendon, which anchors the eyelids to the nose, can result in severe swelling and functional impairment.
Recognizing Urgent Symptoms
While many instances of mild swelling resolve with conservative treatment, certain signs necessitate prompt evaluation by a healthcare provider. Rapidly increasing swelling that spreads beyond the immediate medial canthus area and affects the entire orbit or eyelid suggests a more serious condition. This diffuse swelling may indicate orbital cellulitis, an infection of the tissues surrounding the eye.
Severe, unrelenting pain, or pain accompanied by a fever or chills, indicates an infection requiring immediate antibiotic treatment. Any change in vision, such as blurriness or double vision, is an urgent symptom, as it may signal that the infection or mass is exerting pressure on the eyeball or optic structures. Additionally, any non-healing sore, nodule, or lesion that bleeds easily and continues to grow should be examined to rule out malignancy.