Open-angle glaucoma is the most common form of adult glaucoma and can lead to loss of vision or blindness. This type of glaucoma can only be detected by your eye care practitioner through a routine eye examination. Open-angle glaucoma occurs when the eye's drainage system becomes clogged over time. A part of this system, called the trabecular meshwork, is a tiny spongy tissue that allows fluid to leave the eye. This structure is situated in the eye's angle where the iris and cornea meet. When this drain becomes clogged, aqueous fluid cannot leave the eye as fast as it is produced, causing the fluid to back up. This backed-up fluid increases pressure in the eye and can cause damage to eyesight. If open-angle glaucoma is not diagnosed and treated, it can cause a gradual loss of vision. This type of glaucoma develops slowly and usually without symptoms.