A red line in the eye with sudden onset of symptoms may be subconjunctival hemorrhage, related to trauma, inflammation or systemic disease. Subconjunctival hemorrhage due to trauma is mostly caused by mild bumping and rubbing of the eye, and the patient has no significant discomfort and waits for self-absorption. If there is pain, photophobia, and tearing, it may be related to inflammation. Viral infectious conjunctivitis and keratitis are the only signs of subconjunctival hemorrhage, and there may be enlarged preauricular lymph nodes, lid conjunctival follicles, and dendritic diagram-like keratopathy in keratitis. Early treatment with antiviral eye drops and, if necessary, additional non-steroidal anti-inflammatory drugs. Systemic diseases including hypertension, renal diseases, hematological diseases, infectious diseases, etc., cause most of the bleeding to be recurrent due to the fragility of blood vessels or the presence of abnormalities in coagulation function.