Subconjunctival hemorrhage results from rupture of one of the small conjunctival blood vessels with extravasation of blood into the potential space between the conjunctiva and the underlying sclera. The conjunctiva is a thin, transparent mucous membrane covering the anterior sclera, with abundant superficial vasculature including arterioles, venules, and capillaries that are vulnerable to mechanical disruption from minor trauma or pressure changes. Because the bleeding is contained beneath the transparent conjunctiva and limited by the firm scleral surface beneath, the hemorrhage appears dramatically as a bright red, well-circumscribed area without ability to penetrate deeper structures.
Most subconjunctival hemorrhages are spontaneous without identifiable cause, particularly in older adults whose vessels become more fragile with age. Common predisposing factors include sudden Valsalva maneuvers (coughing, sneezing, vomiting, straining at stool, heavy lifting, vigorous nose blowing), eye rubbing or trauma, contact lens use, and minor eye irritation. Systemic conditions associated with increased risk include hypertension, diabetes mellitus, bleeding disorders (von Willebrand disease, thrombocytopenia, hemophilia), liver disease causing coagulopathy, and use of anticoagulants (warfarin, direct oral anticoagulants) or antiplatelet agents (aspirin, clopidogrel). Recurrent hemorrhage in younger patients warrants investigation for underlying coagulopathy.
Clinical presentation is characteristic: dramatic painless redness in well-circumscribed area, typically temporally or nasally, without associated visual change, photophobia, discharge, or foreign body sensation. The blood appears bright red initially, gradually changing through orange and yellow as it resolves over 1-3 weeks. Differential diagnosis includes other causes of red eye that warrant exclusion: bacterial or viral conjunctivitis (presents with discharge, often bilateral), uveitis (with pain, photophobia, vision change), acute angle closure glaucoma (severe pain, halos, vision loss), corneal ulcer (with pain and visual disturbance), scleritis (severe boring pain, often associated with autoimmune disease), and orbital cellulitis. No specific treatment is required; cool compresses initially may provide comfort, with warm compresses after 48 hours potentially aiding resolution. Lubricating drops may help if there is mild irritation. Evaluation includes blood pressure measurement, history for trauma or systemic risk factors, and consideration of coagulation studies in recurrent or bilateral cases. Recurrent hemorrhages require systemic workup.