Glaucoma is actually a family of eye diseases that cause loss of vision. The two main types are open-angle and angle-closure. These can be either primary, when the cause is not known, or secondary, when the cause is known to be something like an eye injury or a disease. Symptoms of secondary glaucoma may vary depending on the cause.

Open-Angle Glaucoma Symptoms

• Usually symptoms are not noticeable until the disease is at an advanced stage.
• Peripheral vision is lost first, gradually progressing to tunnel vision and eventually complete blindness.
• Open-angle glaucoma usually affects both eyes, although sometimes vision loss occurs only in one eye at first.

Angle-Closure Glaucoma Symptoms

• This type of glaucoma develops suddenly because of a sharp rise in pressure within the eye.
• An attack usually occurs at night or in a dark room, when the pupils are very dilated.
• An attack may be very painful.
• Permanent loss of vision can occur within 24 hours of the attack, so seek medical attention immediately if you think you are having an attack.

Symptoms of an attack:

• Blurry vision
• Halos or bright rings around lighted objects
• Redness of the eye
• Extreme eye pain
• Nausea or vomiting

Causes of Glaucoma

• One of the most well-understood causes that contribute to glaucoma is intraocular pressure, or pressure within the eyeball. This pressure helps your eye hold its shape and function correctly. If the pressure is too high, the optic nerves can be damaged. Your eyes are constantly producing and draining fluid to keep themselves clean and healthy. Sometimes, the drain can become blocked, causing the pressure in the eye to increase. However, high eye pressure does not always cause glaucoma. Some people with high pressure in their eyes never develop glaucoma.
• Sometimes the optic nerve is damaged without an increase in pressure. This is called low-tension glaucoma. This type of glaucoma is not understood very well. Doctors have speculated that a loss of blood flow to the eye resulting from vascular diseases may cause glaucoma.
• Age may be a factor in glaucoma. People over 60 are at an increased risk of glaucoma, and African Americans over 40 also have increased risk.
• Certain ethnic groups have a higher risk for glaucoma than others. African Americans are more prone to glaucoma than Caucasians and are much more likely to go blind. Mexican Americans also have a higher risk. Asians have a higher risk of angle-closure glaucoma, while people of Japanese descent are more likely to get low-tension glaucoma. Doctors do not know why certain ethnic groups are more prone to glaucoma than others.
• People with a family history of glaucoma are more likely to develop it.
• Certain conditions like diabetes, hypertension, or heart disease have also been found to increase a person’s risk for developing glaucoma.
• Eye injuries, deformities, near sightedness, and corticosteroid use have all been linked to glaucoma.

Sources:
http://www.glaucoma.org/index.php
http://www.mayoclinic.com/health/glaucoma/DS00283/DSECTION=4