One of the most common presenting symptom in ophthalmology I red eye. It is the manifesting sign of many ocular diseases; can be acute or chronic, mild or severe, unilateral or bilateral. The etiology can be infectious, allergic, autoimmune, inflammatory or traumatic (probably most common). Pathologies of each of the orbit, eyelid, conjunctiva, cornea, sclera, episcleral and even the posterior uveal tract can all manifest as a red eye