What causes redness at the medial canthus (inside corner of the eye) without surrounding redness?

Redness at the Medial Canthus (Inside Corner of Eye)

Isolated redness at the medial canthus without surrounding conjunctival or periocular involvement most commonly represents localized irritation, punctal inflammation, or early canaliculitis, though dupilumab-related ocular surface disease should be considered in patients on this medication. 1

Primary Differential Diagnosis

The medial canthus can develop isolated redness from several distinct mechanisms:

Localized Inflammatory Conditions

• Punctal inflammation or stenosis can cause focal redness at the medial canthus where the tear drainage system opens, often associated with chronic irritation or medication exposure 1
• Early canaliculitis presents with localized redness and swelling around the punctum, typically unilateral, and may progress to purulent discharge if untreated 1
• Medication-induced keratoconjunctivitis characteristically causes punctal edema and redness, particularly with chronic topical medication use (glaucoma drops, antibiotics, preservatives), and this can be isolated to the medial canthus region 1

Drug-Related Causes

• Dupilumab-associated ocular surface disease presents with bilateral conjunctival and limbal injection, though it can be asymmetric, and typically develops within weeks to months of starting treatment in patients with severe atopic dermatitis 1
• This condition shows watery or mucous discharge and may have follicular or papillary changes, but isolated medial canthus involvement would be atypical 1

Mechanical and Anatomical Factors

• Conjunctival chalasis (redundant conjunctiva) can cause localized redness when the redundant tissue accumulates near the medial canthus and may occlude the inferior puncta 1
• Floppy eyelid syndrome can cause chronic irritation with focal redness, though this typically involves superior tarsal changes 1

Critical Red Flags Requiring Urgent Evaluation

Unilateral redness should always prompt consideration of other causes beyond simple conjunctivitis, as bilateral involvement is typical for most inflammatory conditions. 1

The RAPID acronym identifies emergent features requiring same-day ophthalmology referral (< 24 hours): 1

• Redness with other concerning features
• Acuity loss (vision decrease)
• Pain (moderate to severe, not just irritation)
• Intolerance to light (photophobia)
• Damage to cornea (fluorescein uptake, ulceration, haze, opacity, purulent discharge)

Diagnostic Approach

Initial Assessment

• Determine laterality: Unilateral isolated medial canthus redness suggests localized punctal/canalicular pathology rather than diffuse conjunctivitis 1
• Assess for discharge: Purulent discharge suggests bacterial canaliculitis; watery discharge suggests irritation or medication effect 1, 2
• Medication history: Document all topical eye medications, including over-the-counter lubricants, as preservatives commonly cause punctal inflammation 1
• Systemic medications: Specifically ask about dupilumab use in patients with atopic dermatitis 1

Physical Examination Findings

• Inspect puncta: Look for stenosis, keratinization, edema, or purulent material expressible from punctum 1
• Evaluate conjunctiva: True conjunctivitis shows diffuse hyperemia with discharge, follicles, or papillae—not isolated medial canthus redness 2
• Check for sectoral pattern: Localized redness without diffuse involvement suggests mechanical irritation or focal inflammation rather than infectious/allergic conjunctivitis 2

Management Algorithm

For Isolated Medial Canthus Redness Without Red Flags

Mild cases without discharge or pain:

• Initiate preservative-free lubricants 2-4 times daily 1
• Discontinue any topical medications if possible to assess for medication-induced inflammation 1
• Warm compresses to medial canthus area if punctal inflammation suspected 1

If associated with medication use:

• Switch to preservative-free formulations of all topical medications 1
• Consider medication-induced keratoconjunctivitis and gradually discontinue offending agents when medically appropriate 1

If purulent discharge present:

• Suspect canaliculitis and refer to ophthalmology within 1-2 weeks for possible probing/irrigation and topical antibiotics 1

For Dupilumab Users with New Ocular Symptoms

Mild to moderate severity (bilateral redness, watery/mucoid discharge): 1

• Start preservative-free lubricants 2-4 times daily
• Add olopatadine twice daily if moderate severity
• Continue dupilumab and reassess in 1-2 weeks
• Refer to ophthalmology within 4 weeks if not improving

Severe presentation or any red flag features: 1

• Urgent ophthalmology referral within 24 hours
• Start preservative-free lubricants immediately
• Do not discontinue dupilumab without specialist consultation

Common Pitfalls to Avoid

• Assuming all eye redness is conjunctivitis: Isolated medial canthus redness without diffuse conjunctival injection, discharge, or inflammatory signs is not typical conjunctivitis 2
• Missing medication-induced causes: Chronic topical medication use (especially with preservatives) commonly causes punctal inflammation that may be mistaken for infection 1
• Overlooking unilateral presentation: Bilateral involvement is typical for most inflammatory conditions; unilateral isolated redness warrants closer evaluation for focal pathology 1, 2
• Treating with topical antibiotics empirically: This may worsen medication-induced inflammation and delay correct diagnosis 1