The redness of the eyeball is caused by many reasons, and the common causes are as follows: a. Subconjunctival hemorrhage, which is manifested as patchy redness of the white eyeball, is caused by microvascular rupture, such as eye rubbing, coughing, vomiting, high blood pressure, and eye fatigue. This needs to be treated with cold compresses, and hot compresses can be applied after 2-3 days to promote blood absorption. Second, acute conjunctivitis, in addition to eye redness, also shows increased secretions, such as yellowish-white secretions, tear-like secretions or mucus-like secretions. Further examination at the hospital is required to determine the type of conjunctivitis and to treat it accordingly. Third, keratitis with red eyes and associated photophobia, tearing and blurred vision. Prompt hospital visits should be made for detailed diagnosis. IV. Iriditis, iridocyclitis, is a redness of the eye caused by inflammation of the eye. V. Acute angle-closure glaucoma, which not only manifests as eye redness, but also as eye distention, nausea, vomiting, and blurred vision, should be promptly seen by a regular eye care provider.