The term glaucoma means increased fluid pressure in the front part of the eye. It is a condition that affects about 1% of the population and is much more common in people who are over 50 years old. Trabeculectomy is an operation that is performed to allow free drainage of this fluid. The front part of the eye has two chambers. The first one is the space between the cornea (the transparent 'film' in the centre of the eye) and the iris which is the coloured, rounded part behind it. The open centre of the iris is the pupil. The second chamber is just behind the first and is the space between the back surface of the iris and the lens of the eye.