Glaucoma is a group of diseases in which the optic nerve becomes damaged. Once damaged, characteristic visual field changes occur. There are many types of glaucoma. Some types are hereditary, while other types are not.

Research indicates two interrelated processes leading to primary open angle glaucoma, the most common type of the disease. First, the eye may produce too much fluid (aqueous humor) for itself. Or second, the eye’s drainage system may be blocked. Either one or both processes may occur causing the inside pressure of the eye (intraocular pressure or IOP) to increase. The pressure builds up enough to squeeze the small blood vessels in the eye. This reduces the circulation of blood and damages the nerves that relay vision. The first nerves to be affected are usually the ones that transmit peripheral or side vision. With most types of glaucoma, pressure increases are so mild that there is no feeling of pressure or pain. Therefore, changes occur so slowly that a person is not usually aware of vision loss.

It was once believed that high IOP was the main cause of this optic nerve damage. Although IOP is clearly a risk factor, we now know that other factors must be involved. People with “normal” IOP can experience vision loss from glaucoma, while people with high “IOP” may not experience vision loss (a condition known as ocular hypertension).

Glaucoma can be difficult to diagnose because it is usually a slow process. Many different tests may be necessary to assist your doctor in establishing a diagnosis. These tests may include but not be limited to the following: tonometry, gonioscopy, ophthalmoscopy, visual fields, and retinal tomographs.

• Tonometry is a test that measures IOP. Intraocular pressure varies from one person to the next. With glaucoma, the pressure can vary throughout the day: being normal part-time and high part-time. Several IOP tests are necessary when your eye doctor is suspicious of glaucoma.
  
• Gonioscopy is a test that evaluates the drainage structures of your eyes. Your doctor will use a special handheld lens and a microscope to see if there are any changes causing glaucoma.
  
• Ophthalmoscopy allows your doctor to see the retina and optic nerves inside your eyes. The nerves are best viewed with the eyes dilated. Some eyes have a natural appearance that is very similar to eyes with early glaucoma. These eyes need to be watched very carefully for subtle changes. With glaucoma, eyes do change internally.
  
• Perimetry uses a sophisticated computer to measure and analyze your visual field or peripheral vision. Your doctor will be looking for stable peripheral vision. A decrease my indicate glaucoma. Repeated visual field tests are needed to determine if your peripheral vision is changing.
  
• Tomography assists with early detection of glaucoma. The Heidelberg Retina Tomograph II (HRT II) uses CAT-scan-like technology to create a detailed 3-D “picture” of the optic nerve head and surrounding tissues. In short, the HRT II informs your doctor if your optic nerves are structurally set up to develop glaucoma.
  
  Your doctor may recommend some or all of these tests when there are risks of glaucoma; such as family history, high or borderline IOP measurements, certain medication usage or questionable appearance of internal eye structures. When these tests are ordered, your doctor is not necessarily saying that you have glaucoma. Your doctor needs more information about your eyes. This information provides baseline data for comparisons when evaluating your eyes in the future. With this information, your doctor will be most accurate in determining whether or not your eyes are developing glaucoma.
  
  Treatment of glaucoma involves lowering the pressure of the eye to prevent further damage. Treatment includes various medications or even surgery to control the IOP. Routine eye examinations are extremely important, because if glaucoma is left untreated, permanent vision loss or blindness occurs.