Keeping your sight test up to date is not just about updating your prescription. A sight test can detect all different eye conditions.
Glaucoma is the name given to a group of eye conditions in which the main nerve to the eye (the optic nerve) is damaged where it leaves the eye. This nerve carries information about what is being seen from the eye to the brain and as it becomes damaged, vision is lost. This results in misty and patchy vision, with eventual loss of central vision, although this is rare.
Although any vision which has been lost to glaucoma cannot be recovered, with early diagnosis, careful monitoring and regular use of treatments, the vast majority of people retain useful sight for life. The only way to know if you have glaucoma is to have your eyes checked at your local optometrist (optician).