What causes glaucoma?
Clear liquid called aqueous humor circulates inside the front portion of the eye. To maintain a healthy level of pressure within the eye, a small amount of this fluid is produced constantly while an equal amount flows out of the eye through a microscopic drainage system. (This liquid is not part of the tears on the outer surface of the eye.)
Because the eye is a closed structure, if the drainage area for the aqueous humor – called the drainage angle – is blocked, the excess fluid cannot flow out of the eye. In some forms of glaucoma, fluid pressure within the eye increases, pushing against the optic nerve and causing damage. Clear liquid called aqueous humor is constantly being produced within the eye (left). If the drainage angle of the eye is blocked, fluid cannot flow out of the eye (right).
What are the different types of glaucoma?
Chronic open-angle glaucoma:
This is the most common form of glaucoma in the United States and represents over 95 % of the glaucoma treated at the Phillips Eye Center. Currently, over 2 million adults in the US have glaucoma and the number is increasing each year. Since one of the main risk factors for developing glaucoma is age, the stage is set for ever increasing numbers of active glaucoma patients in the US as life expectancy increases.
The risk of developing chronic open-angle glaucoma increases with age. The drainage angle of the eye becomes less efficient over time, and pressure within the eye gradually increases, which can damage the optic nerve. In some patients, the optic nerve becomes sensitive even to normal eye pressure and is at risk for damage. Treatment is necessary to prevent further vision loss.
|Early||Moderate||And advanced optic nerve damage from glaucoma|
Typically, open-angle glaucoma has no symptoms in its early stages and vision remains normal. As the optic nerve becomes more damaged and fibers are lost, blank spots begin to appear in the field of vision. Since the early stages of glaucoma can be symptom-less, early detection is crucial and is often the result of a careful eye exam coupled with testing such as visual field testing and laser nerve analysis. These tests are available at the Phillips Eye Center, where we have a Zeiss-Humphrey visual Field Analyzer as well as the Stratus OCT laser nerve analyzer. The latter of these devices measures the amount of nerve tissue present in the eye to a resolution of approximately ten microns ( about the length of a red blood cell). These tests, while important, are only part of the process to evaluate a patient for glaucoma. The results are considered in light of other findings from the eye exam and other risk factors that may be present.
Visual field machine
Some eyes are formed with the iris (the colored part of the eye) too close to the drainage angle. In these eyes, which are often small and farsighted, the iris can be sucked into the drainage angle and block it completely. Since the fluid cannot exit the eye, pressure inside the eye builds rapidly and causes an acute closed-angle attack.
Symptoms may include:
- blurred vision
- severe eye pain
- rainbow-colored halos around lights
- nausea and vomiting
This is a true eye emergency. If you have any of these symptoms seek medical attention immediately. Unless this type of glaucoma is treated quickly, damage to your vision can occur.
Who is at risk for glaucoma?
The most important risk factors include:
- Age (over 65)
- Elevated eye pressure ( over 22)
- Family history of glaucoma
- African or Spanish-American ancestry
- Farsightedness or nearsightedness
- Past eye injuries
- Thinner central corneal thickness
How is glaucoma detected?
Detecting glaucoma involves more than just checking your pressure. A glaucoma screening that checks only the pressure of the eye is not sufficient to determine if you have glaucoma since glaucoma can develop in the setting of normal eye pressures. The only sure way to detect glaucoma is to have a complete eye examination, including a dilated exam and evaluation of the optic nerve. Some of the new diagnostic advances in nerve imaging, such as the Zeiss OCT often help us detect glaucoma earlier than previously possible.
Patients with any of the first three risk factors listed above should have a full glaucoma exam.
- It is estimated that over 3 million Americans have glaucoma but only half of those know they have it.
- Approximately 120,000 are blind from glaucoma in the United States.
- About 2% of the population ages 40-50 and 8% over 70 have elevated IOP.
- Estimates put the total number of suspected cases of glaucoma at around 65 million worldwide.
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