Glaucoma is the result of damage to the optic nerve. As this nerve gradually deteriorates, blind spots develop in visual field. It's often linked to a build up of pressure inside your eye. If the damage worsens, glaucoma can cause permanent vision loss or even total blindness within a few years.

The fluid inside your eye, called aqueous humor, usually flows out of your eye through a mesh-like channel. If this channel gets blocked, or the eye is producing too much fluid, the liquid builds up. Less-common causes of glaucoma include a blunt or chemical injury to your eye, severe eye infection, blocked blood vessels inside your eye, and inflammatory conditions. 

Open-angle glaucoma This is the most common type. Your doctor may also call it wide-angle glaucoma. The drain structure in your eye (called the trabecular meshwork) looks fine, but fluid doesn’t flow out like it should.

Angle-closure glaucoma This is more common in Asia. You may also hear it called acute or chronic angle-closure or narrow-angle glaucoma. Your eye doesn’t drain like it should because the drain space between your iris and cornea becomes too narrow. This can cause a sudden buildup of pressure in your eye. It’s also linked to farsightedness and cataracts, a clouding of the lens inside your eye.

Secondary glaucoma glaucomawhen another condition, like cataracts or diabetes, causes added pressure in your eye.
Normal-tension glaucoma This is when you have blind spots in your vision or your optic nerve is damaged even though your eye pressure is within the average range. Some experts say it’s a form of open-angle glaucoma.
Pigmentary glaucoma:With this form, tiny bits of pigment from your iris, the coloured part of your eye, get into the fluid inside your eye and clog the drainage canals.

Most people with open-angle glaucoma don’t have symptoms. If symptoms do develop, it’s usually late in the disease. That’s why glaucoma is often called the "sneak thief of vision." The main sign is usually a loss of side, or peripheral, vision. Symptoms of angle-closure glaucoma usually come on faster and are more obvious. Damage can happen quickly. If you have any of these symptoms, get medical care right away:

• Seeing halos around lights
• Vision loss
• Redness in your eye
• Eye that looks hazy (particularly in infants)
• Upset stomach or vomiting
• Eye pain