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Glaucoma is a disease of the optic nerve, which is the cable through which images you see from the eye are transmitted to the brain. The optic nerve is made up of numerous nerve fibers (like an electric cable made up of many wires). Glaucoma damages nerve fibers, which can cause blind spots and loss of vision.
Glaucoma has to do with the pressure inside the eye, or intraocular pressure (IOP). When the aqueous humor (the clear liquid that normally flows in and out of the eye) cannot drain properly, pressure builds up in the eye. The resulting increase in IOP can damage the optic nerve.
Glaucoma causes no symptoms early in its course; you will not experience pain or vision changes while it is developing. The best way to protect yourself and your family members against vision loss from glaucoma is by being aware of your higher risk of developing this disease and by having regular eye examinations for glaucoma at appropriate intervals. If you are diagnosed with glaucoma, please make sure to tell your family members and urge them to have an eye exam for glaucoma.
Here are some resources for more information on glaucoma:
Glaucoma EvaluationBecause it has no noticeable symptoms, glaucoma is a difficult disease to detect without regular, complete eye exams. During a glaucoma evaluation, your ophthalmologist (Eye M.D.) will perform the following tests:
- Tonometry Your ophthalmologist measures the pressure in your eyes (intraocular pressure, or IOP) using a technique called tonometry. Tonometry measures your IOP by determining how your cornea responds when an instrument presses on the surface of your tear film. Eye drops are usually used to numb the surface of your eye for this test.
- Gonioscopy. For this test, your ophthalmologist inspects your eye’s drainage pathway which sits in the angle between the cornea, the clear front part of the eye, and the iris, the colored part of the eye. This ‘angle’ is where fluid drains out of your eye. During gonioscopy, you sit in a chair facing the microscope used to look inside your eye. You will place your chin on a chin rest and your forehead against a support bar while looking straight ahead. The goniolens is placed lightly on the front of your eye, and a narrow beam of light is directed into your eye while your doctor looks through the slit lamp at the drainage angle. Drops will be used to numb the eye before the test.
- Ophthalmoscopy. With this test, your ophthalmologist can evaluate whether or not there is any optic nerve damage by looking at the back of the eye (called the fundus). There are two types of ophthalmoscopy: direct and indirect. With direct ophthalmoscopy, your ophthalmologist uses a small flashlight-like instrument with several lenses that magnifies up to about 15 times. This type of ophthalmoscopy is most commonly done during a routine physical examination. With indirect ophthalmoscopy, the ophthalmologist wears a headband with a light attached and uses a small handheld lens to look inside your eye. Indirect ophthalmoscopy allows a better view of the fundus, even if your natural lens is clouded by cataracts.
- Visual Field Test The peripheral (side) vision of each eye is tested with visual field testing, or perimetry. For this test, you sit at a bowl-shaped instrument called a perimeter. While you stare at the center of the bowl, lights flash. Each time you see a flash, you press a button. A computer records your response to each flash. This test shows if you have any areas of vision loss. Loss of peripheral vision is often an early sign of glaucoma.
- Photography Sometimes photographs or other computerized images are taken of the optic nerve to inspect the nerve more closely for damage from elevated pressure in the eye.
- Special imaging Different scanners may be used to better determine the configuration of the optic nerve head or retinal nerve fiber layer.
- Pachymetry This measures the thickness of the central cornea. A thin cornea has been shown to be a risk factor for the development of glaucoma, and may be an indication that your IOP reading is an underestimation, although there has not been a direct correlation demonstrated between central corneal thickness and IOP.
Glaucoma – African and Hispanic Ancestry
If you are of African or Hispanic ancestry and especially if you have a known family member with glaucoma, you are at a higher risk for vision loss from this eye disease.
Primary open-angle glaucoma is the leading cause of blindness among people of African ancestry, occurring at a rate four times higher than among Caucasian patients. It also occurs about 10 years earlier among people of African ancestry than among Caucasians and develops more rapidly. Studies show that in the United States, African Americans between the ages of 45 and 64 are approximately 15 times more likely to go blind from glaucoma than Caucasians with glaucoma in the same age group. Primary open-angle glaucoma is also the leading cause of blindness among people of Hispanic (and especially Mexican) ancestry, occurring at a rate approaching that of people of African ancestry.
It is not clear why people of African ancestry have higher rates of glaucoma and subsequent blindness than Caucasians. One factor may be that they are more susceptible to developing elevated IOP earlier in life, which is thought to contribute to optic nerve damage and eventual vision loss. Another reason may be that they are less likely than Caucasians to have early eye examinations that might detect and treat glaucoma. This also may be a factor in the increased rate of glaucoma among Hispanics.
Recommended intervals for a comprehensive eye evaluation in people of African ancestry are as follows:
- 20 to 29 years of age: every 3 to 5 years
- 30 to 64 years of age: every 2 to 4 years
- 65 years and older: every 1 to 2 years
Intraocular PressureElevated intraocular pressure (high pressure within the eye) is a strong risk factor for glaucoma. However, elevated intraocular pressure (IOP) does not always cause glaucoma. It becomes relevant because it is the modificable factor that is addressed in the treatment of glaucoma: all of the glaucoma treatment interventions, whether eye drops, laser, or incisional surgery, are designed to lower the IOP. The average eye pressure in adults, based on normative population data, ranges between 10 mm Hg and 21 mm Hg (“mm Hg” stands for “millimeters of mercury”). There can be a significant difference in your IOP throughout the course of a day. This variation is known as diurnal fluctuation. We know that many patients with IOP in the 20s do not develop glaucoma. Up to 50% of patients diagnosed with glaucoma have an initial pressure reading lower than 22 mm Hg. Intraocular pressure is not a very sensitive tool for diagnosing glaucoma, but it becomes very useful in monitoring treatment for glaucoma as mentioned previously. A variety of methods can be used to check the intraocular pressure, but the most common is applanation tonometry. Your ophthalmologist (Eye M.D.) will often set a “target” pressure for you and will work hard to keep the pressure at or below that target to help preserve your vision. This target pressure is often initially set at a point that is 20-33% below your known maximum eye pressure.
Visual Field TestingBecause it has no noticeable symptoms, glaucoma is a difficult disease to detect without regular, complete eye exams. One particular test, called a visual field test (or perimetry test), measures all areas of your eyesight, including your side, or peripheral vision. A visual field test can help find certain patterns of vision loss and is a key way to check for glaucoma. It is very useful in finding early changes in vision caused by nerve damage from glaucoma. To take this painless test, you sit at a bowl-shaped instrument called a perimeter. While you stare at the center of the bowl, lights flash. Each time you see a flash you press a button. A computer records the location of each flash and whether you pressed the button when the light flashed in that location. At the end of the test, a printout shows if there are areas of your field of vision where you did not see the flashes of light. This test shows if you have any areas of vision loss. Loss of peripheral vision is often an early sign of glaucoma. Regular perimetry tests are an important technique for learning how, if at all, your vision is changing over time. It can also be used to see if treatment for glaucoma is preventing further vision loss.
Nerve-Fiber-Layer AnalysisEarly in the disease process of glaucoma, individual nerve fibers in the eye’s optic nerve are lost, causing an associated pattern of nerve-fiber-layer thinning. This problem can later translate into loss of tissue at the optic nerve head, resulting in visual field defects and, ultimately, loss of vision. New techniques have been devised to help measure the thickness of the nerve fiber layer, helping ophthalmologists (Eye M.D.s) diagnose glaucoma earlier and monitor progression of the disease. One technique uses a low-power laser light and a process called optical coherence tomography (OCT). This imaging technique can help provide an objective measurement of the nerve fiber layer by detecting microns (thousandths of a millimeter) of thickness of the nerve fiber layer, enhancing the ability to effectively diagnose and monitor glaucoma. Both tests are done in the ophthalmologist’s office. During these tests, the patient is required only to remain still while the image is scanned.
Neovascular GlaucomaNeovascular glaucoma is a particularly aggressive and difficult to treat kind of glaucoma. It is caused by new, small blood vessels growing in the front part of the eye. These new, tiny, and fragile vessels (called ‘neovascularization’) grow on the surface of the iris (the colored part of the eye) and over the drainage channel, blocking the flow of fluid from the eye, creating a plumbing issue within the eye. This causes a rapid and painful rise in pressure within the eye. This type of glaucoma often does not respond well to medical treatment, and the high intraocular pressure can lead to a rapid loss of vision. The root cause of neovascularization is poor blood and oxygen supply to the retina. The three most common causes of neovascular glaucoma include diabetic retinopathy, retinal vein and artery occlusions, and carotid artery disease. There are other less common causes of this type of glaucoma. The prognosis for neovascular glaucoma is very guarded. The root cause of poorly controlled blood glucose, poorly controlled blood pressure, or occlusive carotid disease must be addressed with the patient’s co-managing physicians to mitigate disease. The neovascularization can be mitigated with retinal laser treatment called panretinal photocoagulation (PRP) or anti-VEGF injections into the vitreous cavity. If the high eye pressure persists, treatment can include medication or surgery. Because of the risk of scarring with a trabeculectomy, tube shunt surgery is often recommended. The goal in treating neovascular glaucoma is to lower the intraocular pressure, preserve vision, and maintain a comfortable eye.
Pseudoexfoliation GlaucomaPseudoexfoliation glaucoma is a relatively common form of open-angle glaucoma that can cause significantly high eye pressures. This condition is marked by a dust-like material that is observed inside the eye on the surface of the iris and lens. This material can clog the ocular drainage system, increasing intraocular pressure (IOP). It can occur in one or both eyes and is most commonly seen in patients over the age of 70. Pseudoexfoliation glaucoma is found in all ethnic groups, but it is most commonly seen in people of Scandinavian ancestry. Treatment is often required for pseudoexfoliation glaucoma, consisting of medication, laser treatment, or surgery. Pseudoexfoliation can cause increased complications with cataract surgery. With proper treatment and monitoring, patients with pseudoexfoliation glaucoma tend to do well. Early diagnosis is important. While some people may experience side effects from medications or surgery, the risks associated with these side effects should be balanced against the greater risk of leaving glaucoma untreated and losing your vision.
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Camp Lowell Surgery Center
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