Iritis is an inflammation of the coloured part of the eye (iris) that can cause redness, pain, light sensitivity, and in some cases, differing pupil sizes. Left untreated, severe iritis can permanently affect vision.

Most people who develop iritis have recurring episodes. Although iritis often occurs for unknown reasons, it can be linked to certain long-term (chronic) diseases that cause inflammation, such as rheumatoid arthritis, inflammatory bowel disease, or other disorders. It may also occur as a result of infection, such as a herpes infection.

Iritis is diagnosed with a complete eye examination. Treatment includes medicines given as eyedrops or by injection next to or inside the eye.