Differential Diagnoses for Unilateral Erythema and Tenderness Around Eye

Immediate Red Flag Assessment

• The American Academy of Ophthalmology recommends urgent evaluation for any patient with visual changes, moderate-to-severe pain, corneal involvement on fluorescein staining, proptosis, painful extraocular movements, or fever, as these indicate vision-threatening conditions requiring same-day ophthalmology referral 1, 2
• Fluorescein staining must be performed in every case to detect corneal involvement that may not be clinically apparent 1

Most Likely Infectious Etiologies

• Adenoviral conjunctivitis presents with unilateral eyelid swelling and erythema, watery discharge, bulbar conjunctival injection, chemosis, and follicular reaction of the inferior tarsal conjunctiva, and is associated with recent exposure to infected individuals or concurrent upper respiratory infection 3, 1
• Herpes Simplex Virus (HSV) infection usually presents unilaterally with bulbar conjunctival injection, watery discharge, mild follicular reaction, and palpable preauricular lymphadenopathy, and can progress to epithelial keratitis, stromal keratitis, corneal scarring, perforation, and uveitis if untreated 3
• Varicella Zoster Virus (VZV) infection usually presents unilaterally with vesicular dermatomal rash or ulceration of eyelids, conjunctival injection, watery discharge, and follicular reaction, and can cause conjunctival scarring, cicatricial ectropion, late corneal anesthesia, and dry eye 3
• Molluscum contagiosum typically presents unilaterally with mild to severe follicular reaction and punctate epithelial keratitis, and is characterized by single or multiple shiny, dome-shaped umbilicated lesions on eyelid skin or margin 3, 1
• Bacterial conjunctivitis can present unilaterally or bilaterally with bulbar conjunctival injection and purulent or mucopurulent discharge, and gonococcal infection can cause corneal infiltrate or ulcer leading to perforation 3

Serious Conditions Requiring Urgent Evaluation

• Preseptal cellulitis presents with eyelid erythema, edema, and tenderness without proptosis, painful eye movements, or vision changes, while orbital cellulitis is a severe infection with proptosis, ophthalmoplegia, vision loss, and fever requiring emergent hospitalization and IV antibiotics 4
• Pediculosis palpebrarum presents unilaterally or bilaterally with follicular conjunctivitis, adult lice at eyelash base, and nits adherent to lash shafts, and is typically sexually transmitted 5
• Sebaceous carcinoma can masquerade as chronic unilateral blepharoconjunctivitis, and biopsy is indicated for unifocal recurrent lesions, resistance to therapy, focal lash loss, or chronic presentation unresponsive to treatment 4

Practical Diagnostic Algorithm

• The American Academy of Ophthalmology recommends ruling out vision-threatening emergencies by checking visual acuity, extraocular movements, proptosis, pupil reactivity, and performing fluorescein staining 1, 4
• Assessing discharge character, examining eyelids carefully, obtaining targeted history, and determining laterality and duration are crucial steps in the diagnostic algorithm 4, 3, 5, 1

Initial Management Approach

• The American Academy of Ophthalmology recommends cool compresses for symptomatic relief and mandatory follow-up in 3-4 days to assess improvement for presumed viral conjunctivitis without red flags 1
• Immediate ophthalmology referral is required for visual changes, moderate-to-severe pain, corneal involvement on fluorescein examination, suspected HSV/VZV with vesicles, or any red flag features 1
• High-dose amoxicillin-clavulanate with daily follow-up is recommended for suspected preseptal cellulitis, and hospitalization for IV antibiotics is necessary if there is no improvement in 24-48 hours or progressive infection 4

Unilateral Eye Pain with Red Inner Eyelids: Differential Diagnosis and Management

Diagnostic Considerations

• The absence of obvious drainage does not exclude bacterial etiology, particularly early in the course, and minimal or absent discharge can occur in early viral conjunctivitis 6
• Enlarged preauricular lymph nodes suggest viral (especially HSV) or Parinaud oculoglandular syndrome, according to the American Academy of Ophthalmology 7

Management Approach

• Assuming "no drainage" excludes infectious conjunctivitis can lead to misdiagnosis, as early viral conjunctivitis may have minimal watery discharge, as noted by the American Academy of Ophthalmology 6

Cited Evidence for Causes of Unilateral Eyelid Swelling

Viral Conjunctivitis (Adenoviral)

• Adenoviral conjunctivitis typically begins with unilateral eyelid swelling and erythema that frequently becomes sequentially bilateral within days【8】.
• The condition presents with watery discharge accompanied by bulbar conjunctival injection【8】.
• A characteristic follicular reaction is seen on the inferior tarsal conjunctiva【8】.
• Chemosis and pre‑auricular lymphadenopathy are common accompanying signs【8】.
• Recent exposure to infected contacts or a concurrent upper‑respiratory infection often precedes onset【8】.
• The disease follows a self‑limited course, with most patients improving within 5–14 days【8】.

Herpes Simplex Virus (HSV) Conjunctivitis

• HSV conjunctivitis usually presents unilaterally【8】.
• Patients exhibit bulbar conjunctival injection together with watery discharge【8】.
• A mild follicular reaction and palpable pre‑auricular lymphadenopathy are typical findings【8】.
• If untreated, the infection can progress to epithelial keratitis, stromal keratitis, corneal scarring, and even perforation【8】.
• Common precipitants include stress, febrile illness, ultraviolet exposure, ocular surgery, or trauma【8】.

Varicella‑Zoster Virus (VZV) Conjunctivitis

• VZV infection usually manifests as unilateral eyelid involvement with a vesicular dermatomal rash or ulceration of the lids【8】.
• Conjunctival injection, watery discharge, and a follicular reaction accompany the rash【8】.
• Potential sequelae include conjunctival scarring, cicatricial ectropion, late‑onset corneal anesthesia, and dry eye【8】.
• A distinctive pleomorphic or non‑excavated pseudodendritic epithelial keratitis may be observed【9】.

Molluscum Contagiosum

• Molluscum typically produces unilateral eyelid disease with a mild to severe follicular reaction【9】.
• Long‑standing lesions can lead to punctate epithelial keratitis and possible corneal pannus【9】.
• Characteristic shiny, dome‑shaped umbilicated papules appear on the eyelid skin or margin【9】.
• The condition is more prevalent in immunocompromised individuals (e.g., HIV)【9】.

Nongonococcal Bacterial Conjunctivitis

• Presents with unilateral or bilateral bulbar conjunctival injection【9】.
• Discharge is purulent or mucopurulent in nature【9】.
• In adults the disease is generally self‑limited but may progress to corneal infection【9】.

Gonococcal Conjunctivitis

• Marked eyelid edema with pronounced bulbar conjunctival injection is typical【10】.
• The discharge is heavily purulent and is often accompanied by pre‑auricular lymphadenopathy【10】.
• A corneal infiltrate or ulcer—frequently beginning superiorly—can develop and may lead to perforation【10】.
• The ocular findings are usually associated with urethritis or pelvic inflammatory disease; in children, sexual abuse should be considered【10】.

Parinaud Oculoglandular Syndrome

• Characterized by unilateral granulomatous follicular conjunctivitis【10】.
• Ipsilateral regional lymphadenopathy (pre‑auricular and submandibular) is commonly present【10】.
• Patients may have fever, eyelid swelling, conjunctival granulomas, and serous discharge【10】.
• The syndrome most often follows infection with Bartonella henselae (cat‑scratch disease) or Francisella tularensis (tularemia)【10】.

Sebaceous Carcinoma (Malignancy)

• May masquerade as chronic unilateral blepharoconjunctivitis, presenting as a hard, non‑mobile tarsal mass with yellowish discoloration【8】.
• The tumor can appear as a subconjunctival, multilobulated yellow mass or mimic a chalazion【8】.

Ocular Surface Squamous Neoplasia (Malignancy)

• Presents with conjunctival hyperemia and papillomatous or sessile nodules【8】.
• Strongly associated with human papillomavirus infection and significant ultraviolet‑light exposure【8】.

Conjunctival Melanoma (Malignancy)

• Appears as a painless, flat or nodular brown or white‑pink lesion on the bulbar or palpebral conjunctiva【8】.
• Enlargement, prominent vascularization, or thickening of the lesion typically prompts clinical presentation【8】.

Chlamydial Conjunctivitis (Less Common)

• Manifests as follicular conjunctivitis with chemosis, papillary hypertrophy, and limbal follicles【10】.

Evaluation and Management of Unilateral Periorbital Dark Circles – Evidence‑Based Guidelines

Allergic Conjunctivitis – Clinical Signs

• Dark infra‑orbital swollen semicircles (allergic facies) are a characteristic finding in chronic allergic conjunctivitis. 11
• Horizontal skin folds (Morgan‑Dennie lines) on the lower eyelid are typical of allergic conjunctivitis. 11
• Pale, boggy nasal turbinates are commonly observed in patients with allergic conjunctivitis. 11
• The discharge is typically clear and watery (may appear pale‑yellow when inflammation is severe). 11

Viral Conjunctivitis – Typical Presentation

• Adenoviral conjunctivitis is the most common cause of unilateral eyelid swelling that can become bilateral within days; it presents with watery discharge, bulbar conjunctival injection, a follicular reaction on the inferior tarsal conjunctiva, and pre‑auricular lymphadenopathy, often after recent exposure to infected individuals or an upper‑respiratory infection. 11

Diagnostic Assessment – Initial Examination

• Pupil reactivity and afferent pupillary defect testing should be performed when initially evaluating unilateral periorbital dark circles to help exclude vision‑threatening emergencies. 12

Management Precautions

• Systemic corticosteroids must not be initiated before an ophthalmology consultation because they can exacerbate herpetic infections or obscure the clinical picture. 12
• The presence of puffy eyelids accompanied by pain, erythema, and warmth suggests pre‑septal cellulitis; this condition requires systemic antibiotic therapy rather than solely topical treatment. 12

Strength of evidence: Not explicitly graded in the cited sources.