I have had three episodes of a painful eye over the past four years. Once it was the right eye, and twice it was the left. The first time it was diagnosed as conjunctivitis, but it didn't get better with antibiotic ointment. Eventually it became so painful that I went to the casualty department, where iritis was diagnosed. I was treated with steroid eye drops and it got better quite quickly. Since then it has come back twice for no apparent reason.

Dr Fred Kavalier answers your health question:

Iritis causes pain, redness and watering of the eye, together with light sensitivity and sometimes blurring of vision. It is not an infection of the eye (unlike conjunctivitis). In fact, it is an autoimmune condition, in which the body produces a reaction against itself. A person who is developing iritis usually feels that the eye is a bit sore and red at first. This quickly progresses to quite a painful eye.

The redness in iritis is concentrated around the iris. This is unlike conjunctivitis, in which the redness tends to be worst near the eyelids. As the inflammation of the iris becomes worse, the pupil can become small and irregularly shaped. People who get iritis sometimes have another underlying condition, such as ankylosing spondilitis, or inflammatory bowel disease. But about half of the people who get iritis get it for no apparent reason. The best way to treat it is with steroid eye drops, and drops to make the pupil open up. You are unlucky that the iritis has come back twice, as it often clears up, never to return.

Please mail your questions for Dr Fred to health@independent.co.uk. He regrets that he is unable to respond personally to questions.