The medial canthus is the inner corner of the eye where the upper and lower eyelids meet. Swelling in this specific location is a symptom that points to an issue with underlying structures, rather than a standalone diagnosis. This swelling can be alarming due to its proximity to the eye, and understanding the anatomy of this region is the first step in determining the cause.
Anatomy of the Medial Canthus
The medial canthus houses the lacrimal, or tear drainage, system. After tears wash over the eye, they enter two tiny openings called puncta, located on the eyelid margins in the inner corner.
From the puncta, tears flow through small tubes (canaliculi) into the lacrimal sac, a reservoir located on the side of the nose. The sac narrows into the nasolacrimal duct, a channel that opens into the nasal cavity. This connection is why crying often causes a runny nose.
Any disruption in this pathway can cause fluid backup, leading to inflammation and swelling. The medial canthus is also near the nasal sinuses, so issues in one area can affect the other. This explains why a problem in the eye’s corner can have roots deeper within the facial structures.
Primary Causes of Medial Canthus Swelling
The most frequent causes of swelling involve infection or blockage of the tear drainage system. Dacryocystitis, an infection of the lacrimal sac, occurs when the nasolacrimal duct becomes blocked. Stagnant tears in the sac create an environment for bacteria to multiply, causing sudden pain, redness, and swelling, often with a pus-like discharge from the puncta when pressed.
A blockage of the nasolacrimal duct without an infection can also cause swelling. This is common in infants whose ducts may not be fully open at birth. In adults, age-related narrowing or stones within the system (dacryoliths) can cause obstruction. Swelling occurs, but the intense pain and redness of an infection are absent.
Inflammatory conditions like contact dermatitis or seasonal allergies can also trigger swelling. This type of reaction is marked by significant itching and watery eyes, often affecting both eyes. The cause is inflammation of the soft tissues, not a blockage.
Direct trauma to the eye or nose can damage tear ducts or cause bruising and fluid buildup. Less commonly, a stye near the inner corner can present as swelling. In rare cases, a tumor in the lacrimal sac or sinuses may cause a firm, painless lump.
The Diagnostic Evaluation
Diagnosis begins with a patient history and physical examination. A provider will ask about the onset of swelling, pain, discharge, and any recent injuries or allergies. During the exam, the doctor inspects the area and may press on the lacrimal sac to check for fluid or pus from the puncta, which indicates blockage or infection.
To assess the tear drainage system, a dye disappearance test may be performed. This test involves placing a fluorescent dye in the eye. If a significant amount of dye remains after five minutes, it confirms a blockage.
If trauma or a tumor is suspected, imaging studies like a CT scan or MRI are ordered. These provide detailed pictures of the lacrimal system and sinuses to identify the cause of an obstruction. For suspected infections, a culture of any discharge can identify the specific bacteria.
Available Treatment Options
For infections like acute dacryocystitis, oral or intravenous antibiotics are used to eliminate the bacteria, and topical antibiotic eye drops may also be prescribed. If swelling is from allergies or contact dermatitis, topical steroid creams and oral antihistamines can reduce inflammation and itching.
At-home measures are often recommended for uncomplicated blockages. Applying warm compresses can relieve discomfort and may help open the blockage. For infants, a gentle massage over the lacrimal sac can help open the membrane causing the obstruction.
If conservative treatments fail, procedural interventions may be necessary. In children, this may involve probing the tear duct to clear the obstruction. For adults with chronic dacryocystitis, a dacryocystorhinostomy (DCR) surgery creates a new bypass for tears to drain from the lacrimal sac into the nose, resolving the blockage.
When to Seek Immediate Medical Care
Certain symptoms associated with medial canthus swelling warrant urgent medical attention, as they can indicate a more serious condition. Seek immediate care if you experience any of the following:
- Swelling that rapidly spreads to the cheek or surrounding orbital area
- Changes in vision, such as blurriness or double vision
- Severe, escalating pain not relieved by simple pain medication
- A high fever accompanying the swelling