Caused by an increase in fluid and hence pressure in the eye pressing against the retina restricting or cutting off the blood supply.
If left untreated will lead to a reduction or complete loss of vision. Any damage is irreparable. Open angle glaucoma is the most common being caused by the gradual blockage of the outflow. Closed angle glaucoma is more serious due to the sudden nature of its development (sudden blockage).
While open angle may display no symptoms closed can include halos round lights pain redness or blurred vision. Neither type should be ignored and as the condition is often hereditary immediate blood relatives should have regular eye examinations and inform their eye-care specialist of any family link.