According to the American Academy of Ophthalmology (AAO), the most common type of glaucoma — called primary open-angle glaucoma — affects an estimated 2.2 million people in the United States, and that number is expected to increase to 3.3 million by 2020 as the U.S. population ages.
Glaucoma usually happens when the fluid pressure inside the eyes slowly rises, damaging the optic nerve. Often there are no symptoms at first, according to the NIH. Without treatment, people with glaucoma will slowly lose their peripheral, or side vision. They seem to be looking through a tunnel. Over time, straight-ahead vision may decrease until no vision remains. A comprehensive eye exam can tell if you have glaucoma. People at risk should get eye exams at least every two years. They include people in these demographics:
• African Americans over age 40
• People over age 60, especially Mexican Americans
• People with a family history of glaucoma
There are several types of glaucoma. The two main types are open-angle and angle-closure, according to www.glaucoma.org . Open-angle Glaucoma, the most common form of glaucoma, accounting for at least 90% of all glaucoma cases:
• Is caused by the slow clogging of the drainage canals, resulting in increased eye pressure
• Has a wide and open angle between the iris and cornea
• Develops slowly and is a lifelong condition
• Has symptoms and damage that are not noticed.
“Open-angle” means that the angle where the iris meets the cornea is as wide and open as it should be. Open-angle glaucoma is also called primary or chronic glaucoma. It is the most common type of glaucoma, affecting about three million Americans.
Angle-closure Glaucoma, is a less common form of glaucoma:
• Is caused by blocked drainage canals, resulting in a sudden rise in intraocular pressure
• Has a closed or narrow angle between the iris and cornea
• Develops very quickly
• Has symptoms and damage that are usually very noticeable
• Demands immediate medical attention.
It is also called acute glaucoma or narrow-angle glaucoma. Unlike open-angle glaucoma, angle-closure glaucoma is a result of the angle between the iris and cornea closing, according to Glaucoma.org. Additionally, other types of this eye disease have also been diagnosed:
Normal-Tension Glaucoma (NTG): Also called low-tension or normal-pressure glaucoma. In normal-tension glaucoma the optic nerve is damaged even though the eye pressure is not very high. We still don't know why some people’s optic nerves are damaged even though they have almost normal pressure levels.
Congenital Glaucoma: This type of glaucoma occurs in babies when there is incorrect or incomplete development of the eye's drainage canals during the prenatal period. This is a rare condition that may be inherited. When uncomplicated, microsurgery can often correct the structural defects. Other cases are treated with medication and surgery.
Other Types of Glaucoma: Variants of open-angle and angle-closure glaucoma include:
• Secondary Glaucoma
• Pigmentary Glaucoma
• Pseudoexfoliative Glaucoma
• Traumatic Glaucoma
• Neovascular Glaucoma
• Irido Corneal Endothelial Syndrome (ICE)
During routine eye exams, a tonometer is used to measure your intraocular pressure, or IOP, according to www.allaboutvision.com . Your eye typically is numbed with eye drops, and a small probe gently rests against your eye's surface. Other tonometers send a puff of air onto your eye's surface. An abnormally high IOP reading indicates a problem with the amount of fluid (aqueous humor) in the eye. Either the eye is producing too much fluid, or it's not draining properly.
Normally, IOP should be below 21 mmHg (millimeters of mercury) — a unit of measurement based on how much force is exerted within a certain defined area. If your IOP is higher than 30 mmHg, your risk of vision loss from glaucoma is 40 times greater than someone with intraocular pressure of 15 mmHg or lower. This is why glaucoma treatments such as eye drops are designed to keep IOP low.
Other methods of monitoring glaucoma involve the use of sophisticated imaging technology — such as scanning laser polarimetry (SLP), optical coherence tomography (OCT) and confocal scanning laser ophthalmoscopy — to create baseline images and measurements of the eye's optic nerve and internal structures. Then, at specified intervals, additional images and measurements are taken to make sure no changes have occurred over time that might indicate progressive glaucoma damage.
Visual field testing is a way for your eye doctor to determine if you are experiencing vision loss from glaucoma. Visual field testing involves staring straight ahead into a machine and clicking a button when you notice a blinking light in your peripheral vision. The visual field test may be repeated at regular intervals to make sure you are not developing blind spots from damage to the optic nerve or to determine the extent or progression of vision loss from glaucoma.
Gonioscopy also may be performed to make sure the aqueous humor (or "aqueous") can drain freely from the eye. In gonioscopy, special lenses are used with a biomicroscope to enable your eye doctor to see the structure inside the eye (called the drainage angle) that controls the outflow of aqueous and thereby affects intraocular pressure. Ultrasound biomicroscopy is another technique that may be used to evaluate the drainage angle. More info can be found at this website: http://www.allaboutvision.com/conditions/glaucoma.htm .
Glaucoma cannot currently be prevented, but if diagnosed and treated early it can usually be controlled. Medication or surgery can slow or prevent further vision loss. However, vision already lost to glaucoma cannot be restored. That is why the American Optometric Association recommends an annual dilated eye examination for people at risk for glaucoma as a preventive eye care measure. Depending on your specific condition, your doctor may recommend more frequent examinations.
Patients with glaucoma need to continue treatment for the rest of their lives. Because the disease can progress or change silently, compliance with eye medications and eye examinations are essential, as treatment may need to be adjusted periodically. By keeping eye pressure under control, continued damage to the optic nerve and continued loss of your visual field may slow or stop. The optometrist may focus on lowering the intraocular pressure to a level that is least likely to cause further optic nerve damage. This level is often referred to as the target pressure and will probably be a range rather than a single number.
Target pressure differs for each person, depending on the extent of the damage and other factors. Target pressure may change over the course of a lifetime. Newer medications are always being developed to help in the fight against glaucoma. Early detection, prompt treatment and regular monitoring can help to control glaucoma and therefore reduce the chances of progression vision loss. Much more information can be found at this website: http://www.aoa.org/Glaucoma.xml .
Regular eye exams are critical for your vision health, especially if you fall into the high risk categories of those individuals more susceptible to this disease. Don’t put off getting your vision checked. Just pretending it won’t happen to you doesn’t mean you may not develop glaucoma. Prevention, regular check ups, and proper care of your vision can help. If you suspect you may be experiencing any problems with your eyes, get an exam with your doctor.
Until next time.
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