What causes a red sclera?

Red Sclera: Causes and Clinical Approach

Red sclera results from inflammation or vascular congestion of the episclera, sclera, or overlying conjunctiva, with the most common causes being conjunctivitis, episcleritis, and scleritis—differentiation is critical as scleritis is sight-threatening and requires urgent ophthalmologic referral. 1, 2

Primary Causes by Anatomic Location

Conjunctival and Episcleral Causes (Most Common)

Conjunctivitis is the most frequent cause of red eye, presenting with:

• Bulbar conjunctival injection with discharge (viral, bacterial, or allergic) 1, 2, 3
• Watery discharge with follicular reaction suggests viral etiology (especially adenoviral) 1
• Mucopurulent discharge indicates bacterial infection 1, 3
• Severe itching with allergen exposure characterizes allergic conjunctivitis 3

Episcleritis presents with:

• Hyperemic sclera and conjunctiva with mild or no pain 1, 4
• Sectoral or diffuse redness without visual changes 1, 4
• Self-limited course resolving within 1-3 months 4
• More common in women aged 40-50 years 4
• In inflammatory bowel disease patients, episcleritis often reflects bowel disease activity 1

Scleral Causes (Sight-Threatening)

Scleritis is distinguished by:

• Moderate to severe eye pain (key differentiating feature from episcleritis) 1, 5
• Deep, boring pain not relieved by topical anesthetics 2
• Visual disturbance and photophobia 1
• Associated with systemic autoimmune diseases (rheumatoid arthritis, inflammatory bowel disease, granulomatosis with polyangiitis) 1, 6
• Can progress to fibrinoid necrosis, vasculitis, and vision loss if untreated 1

Associated Systemic Conditions

Inflammatory Bowel Disease

• Ocular manifestations occur in 4-29% of IBD patients (likely overestimated in tertiary centers) 1
• Episcleritis and anterior uveitis are most common 1
• Scleritis occurs in <1% but is sight-threatening 1

Vasculitis and Autoimmune Disorders

• Sarcoidosis, Kawasaki disease, microscopic polyangiitis, and reactive arthritis can cause conjunctival hyperemia 1
• Rheumatoid arthritis, systemic lupus erythematosus commonly associated with scleritis 6

Atopic and Dermatologic Conditions

• Atopic dermatitis patients may develop conjunctival hyperemia and papillary reaction 1
• Rosacea causes conjunctivitis with eyelid margin disease 1
• Dupilumab-related ocular surface disease presents with hyperemic conjunctiva in 10-42% of treated patients 1

Neoplastic Causes (Rare but Important)

Conjunctival melanoma presents as:

• Painless brown or fleshy-pink lesion with conjunctival hyperemia 1, 7
• Can spread to adnexal structures and metastasize 1, 7

Sebaceous carcinoma may present with:

• Intense bulbar conjunctival injection mimicking chronic blepharoconjunctivitis 1
• History of multiple chalazion excisions 1

Conjunctival lymphoma appears as:

• Painless pink "salmon patch" lesion with indolent fleshy swelling 1
• Associated with autoimmune conditions and chronic infections 1

Critical Differentiation Algorithm

Immediate Ophthalmology Referral Required When:

• Moderate to severe eye pain (suggests scleritis or uveitis) 1, 2
• Photophobia with blurred vision 1
• Visual acuity changes 1, 2
• Pain not relieved by topical anesthetics 2
• Corneal involvement or distorted pupil 2

Simple Episcleritis Does Not Require Referral If:

• Absence of moderate-severe pain 1
• No photophobia or visual blurring 1
• No diminished vision 1

Common Pitfalls

Do not confuse episcleritis with scleritis: The presence of moderate to severe pain is the key distinguishing feature—episcleritis is relatively painless while scleritis causes deep, boring pain 1, 4, 5

Do not miss sight-threatening causes: Scleritis, uveitis, and infectious keratitis require urgent specialist evaluation as delays can result in permanent visual deficits 1, 2

Consider systemic workup: In patients with scleritis or recurrent episcleritis, investigate for underlying autoimmune disease, particularly rheumatoid arthritis, inflammatory bowel disease, and vasculitis 1, 6

Recognize drug-induced causes: Dupilumab therapy for atopic dermatitis causes ocular surface disease in 10-42% of patients, typically within first 4 months of treatment 1