Open angle Glaucoma
This is the most common type of glaucoma, it is painless, and the vision loss is slow and progressive. This is associated with increased pressure in the eye. Not all people with primary open-angle glaucoma have high IOP, but decreasing the eye pressure further has been shown to stop the progression of vision loss.
The increased pressure is caused by trabecular blockage which is where the aqueous humor in the eye drains out. Because the microscopic passageways are blocked, the pressure builds up in the eye and causes imperceptible and very gradual vision loss. Peripheral vision is affected first but eventually the entire vision will be lost if not treated.