The eye constantly produces aqueous, the clear fluid that fills the anterior chamber (the space between the cornea and iris). The aqueous filters out of the anterior chamber through a complex drainage system. Normally, the amount of aqueous humor being produced is equal to the amount that is draining out.

The delicate balance between the production and drainage of aqueous determines the eye's intraocular pressure (IOP). Most people's IOPs fall between 8 and 21.

Glaucoma is a condition in which the normal fluid pressure inside the eyes slowly rises as a result of the fluid aqueous humor not being able to drain properly. Instead, the fluid collects and the pressure builds up in the eye and may ultimately damage the optic nerve and loss of vision. If left untreated, an elevated IOP causes irreversible damage to the optic nerve and retinal fibers resulting in a progressive, permanent loss of vision. However, early detection and treatment can slow, or even halt the progression of the disease.

Open Angle, also called chronic open angle, is the most common type of glaucoma. With this type, even though the anterior structures of the eye appear normal, aqueous fluid builds within the anterior chamber, causing the IOP to become elevated. Left untreated, this may result in permanent damage of the optic nerve and retina. Eye drops are generally prescribed to lower the eye pressure. In some cases, surgery is performed if the IOP cannot be adequately controlled with medical therapy.

Acute angle closure occurs because of an abnormality of the structures in the front of the eye. In most of these cases, the channel between the iris and cornea is more narrow than normal, leaving a smaller channel for the aqueous to pass through. If the flow of aqueous becomes completely blocked, the intraocular pressure rises sharply, causing a sudden angle closure attack. This type of glaucoma is a medical emergency that must be treated by an ophthalmologist immediately. Permanent vision loss can occur within days.

This type occurs as a result of another disease or problem within the eye such as: Inflammation, Trauma, Previous surgery, Diabetes, Tumor and certain medications. For this type, both the glaucoma and the underlying problem must be treated.

This is a rare type of glaucoma that is generally seen in infants. In most cases, surgery is required. In approximately one-third of children, it is inherited through an autosomal recessive gene. Autosomal means that boys and girls are affected equally, and recessive indicates that both parents have the gene.

This is an inherited type of open angle glaucoma that most commonly affects myopic men in their 20s or 30s. Myopia (nearsightedness) causes the eyes to have a concave iris, creating a wide angle. This causes the color (pigment) layer of the eye, the iris, to rub off onto the lens, where it can shed into the aqueous humor and the trabecular meshwork. The pigment can clog the pores of the trabecular meshwork, which prevents adequate aqueous humor drainage and increases IOP.

Normal-tension glaucoma is also known as Low-tension, or Normal-Pressure, Glaucoma. In this type, normal IOP is too high for the individual's optic nerve, leading to damage of the nerve. This condition is rare and poorly understood. It may be that an inadequate blood supply to the optic nerve may cause the damage.