Glaucoma is an eye disease which causes damage to the optic nerve from an intolerable elevation of intraocular pressure. This means that the fluid pressure inside the eye is too high. If left unchecked or uncontrolled, this high pressure will eventually lead to loss of vision. Although there are about 30 different types of glaucoma with various causes and treatments, all have intolerable elevation of intraocular pressure. 

Open Angle Glaucoma
In the most common form of glaucoma, simple glaucoma, there are no symptoms which signal disease. This is because glaucoma first attacks the side or peripheral vision, leaving the straight ahead "detailed" or reading vision perfectly normal. 

Angle Closure or Narrow Angle Glaucoma
In this form of glaucoma, attacks occur which are characterized by pain in the eye or the eyebrow. The pain is often accompanied by halos around lights, blurred vision, nausea and vomiting. 

Glaucoma Pressure Readings
What may be normal pressure for one person may not be normal for another. The average intraocular pressure is somewhere between 8 and 22 millimeters of mercury. Some optic nerves can tolerate a pressure of 30mm with no damage, wheras, other eyes are permanently damaged by a pressure of 15mm. Once an optic nerve is damaged, it can no longer tolerate pressures as high as it once did. 

Surgery 
A control of glaucoma by surgery is usually reserved for those cases in which medicines are not sufficiently effective.