Primary Open-Angle Glaucoma

Primary Open-Angle Glaucoma Overview

The definition of glaucoma has changed drastically since its introduction around the time of Hippocrates in approximately 400 BC.

The word glaucoma came from ancient Greek, meaning clouded or blue-green hue, most likely describing a person with a swollen cornea or who was rapidly developing a cataract, both of which may be caused by chronic (long-term) elevated pressure inside the eye.
 
Pressure inside the eye is termed intraocular pressure. Eye pressure is measured in millimeters of mercury (mm Hg). Normal eye pressure ranges from 10-21 mm Hg. Elevated intraocular pressure is an eye pressure of greater than 21 mm Hg.

The concept of glaucoma has been refined, particularly over the last 100 years. Currently, glaucoma is defined as damage to the optic nerve that is usually caused by high pressure inside the eye. This optic nerve damage can usually be stopped but cannot be reversed by adequate lowering of intraocular pressure.

The generic term glaucoma should only be used to refer to the entire group of glaucomatous disorders, because multiple subsets of glaucomatous disease exist. A more precise term should be used to describe the glaucoma if the specific diagnosis is known.

• One subset of glaucomatous disease is primary open-angle glaucoma.
  
  
  • Primary open-angle glaucoma is described as optic nerve damage from multiple possible causes that is chronic and progresses over time, with a loss of optic nerve fibers that is characteristic of the disease.
    
    
  • In addition to the loss of optic nerve fibers, primary open-angle glaucoma is characterized by open anterior chamber angles, visual field abnormalities, and intraocular pressure that is too high for the continued health of the eye.
    
    
  • Primary open-angle glaucoma exhibits cupping (depression) and atrophy of the optic disc (the front surface of the optic nerve, which is seen in the back of the eye), in the absence of other known causes of glaucomatous disease.
    
    
  • Note that the definition of primary open-angle glaucoma is not synonymous or solely defined by the presence of elevated intraocular pressure. Increased intraocular pressure is a risk factor associated with the development of the disease; increased intraocular pressure is not the disease itself.
  
  
• People can have optic nerve damage without having elevated intraocular pressure. This condition is known as normal-tension (or low-tension) glaucoma.
  
  
• People can also have elevated pressures without signs of optic nerve damage or vision loss. They are considered to be at risk for glaucoma because of the elevated intraocular pressure. In medical terms, these people are known as glaucoma suspects or ocular hypertensives (see Ocular Hypertension and Adult Glaucoma Suspect).
  
  

Primary open-angle glaucoma is a major health concern throughout the world because of its usually silent, progressive nature and because it is one of the leading preventable causes of blindness in the world. With appropriate screening and treatment by an ophthalmologist (a medical doctor who specializes in eye care and surgery), glaucoma can usually be identified and stopped before significant vision loss occurs.