What are the common diseases that cause red eyes?

Red eye, a common symptom in ophthalmology, has several frequent causes: 1. Conjunctivitis: Caused by bacteria, viruses, allergies, or other factors, it manifests as conjunctival congestion and edema, often accompanied by increased discharge, and is one of the most common reasons for red eye. 2. Subconjunctival hemorrhage: Often caused by ocular trauma, eye rubbing, or ocular surgery, it appears as localized bright red or dark red discoloration of the white part of the eye, but usually without other symptoms. 3. Dry eye syndrome: Prolonged use of electronic devices or environmental factors may lead to dry eyes, causing dryness, redness, and possibly a burning sensation or foreign body sensation. 4. Keratitis: Caused by infections, allergies, or autoimmune conditions, keratitis may present with ciliary congestion, along with eye pain and decreased vision. If symptoms such as eye redness or pain occur, it is recommended to seek medical attention promptly to determine the underlying cause and receive appropriate treatment.