Glaucoma 

Introduction
Glaucoma is an eye disorder that occurs from damage to the optic nerve.  The optic nerve carries nerve signals about what you see to your brain for processing.  Glaucoma most frequently results from an imbalance of fluid production and drainage inside of the eye that causes the inner eye pressure to increase. 

Untreated glaucoma can lead to blindness.  Glaucoma is one of the leading causes of blindness worldwide.  Your eye doctor can screen you for glaucoma during your regular eye exam.  Although there is no cure for glaucoma, early detection and treatment can manage the condition and prevent vision loss.

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Anatomy
The vision process occurs as light rays enter the front of your eye and are interpreted by your brain as images.  Light rays first enter your eye through the cornea, a clear dome that helps your eyes focus.
 
The anterior chamber is located behind the cornea and in front of the iris.  The anterior chamber is filled with a fluid that maintains eye pressure, nourishes the eye, and keeps it healthy. This fluid is constantly produced and drained from the anterior chamber into the bloodstream. 
 
The iris is the colored part of your eye.  The iris contains two sets of muscles.  The muscles work to make the pupil of your eye larger or smaller.  The pupil is the black circle in the center of your iris.  It changes size to allow more or less light to enter your eye.
 
After light comes through the pupil, it enters the lens.  The lens is a clear curved disc.  Muscles adjust the curve in the lens to focus clear images on the retina.  The retina is the back part of your eye.
 
Your inner eye or the space between the posterior chamber behind the lens and the retina is the vitreous body.  It is filled with  a clear gel substance that gives the eye its shape.  Light rays pass through the gel on their way from the lens to the retina.
 
The retina is a thin tissue layer that contains millions of nerve cells.  The nerve cells are sensitive to light.  Cones and rods are specialized receptor cells.  Cones are specialized for color vision and detailed vision, such as for reading or identifying distant objects.  Rods perceive blacks, whites, and grays, but not colors.  They detect general shapes.  Rods are used for night vision and peripheral vision.  High concentrations of rods at the outer portions of your retina act as motion detectors in your peripheral or side vision. 
 
The greatest concentration of cones is found in the macula and fovea at the center of the retina.  The macula is the center of visual attention.  The fovea is the site of visual acuity or best visual sharpness.
 
The receptor cells in the retina send nerve messages about what you see to the optic nerve.  The optic nerves extend from the back of each eye and join together in the brain at the optic chiasm.  From the optic chiasm, the nerve signals travel along two optic tracts in the brain and eventually to the occipital cortex.

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Causes
Glaucoma is the term for a group of disorders that lead to optic nerve damage.  Optic nerve damage can cause progressive vision loss and blindness.  People with glaucoma in one eye tend to develop it in the other as well.  Glaucoma most frequently results from an imbalance of fluid production and drainage inside of the eye that causes the inner eye pressure to increase.  However, in a small number of cases, glaucoma results without increased intraocular pressure.
 
There are different types of glaucoma, but most cases are categorized as open-angle glaucoma or closed-angle glaucoma.  Open-angle glaucoma is the most common type of glaucoma.  Open-angle glaucoma results when the anterior chamber angle drainage canals narrow or become clogged over time.  Intraocular pressure increases because fluid is produced at a regular rate, but it drains from the eye at decreased rate.  Closed-angle glaucoma is less common.  It results when the anterior chamber angle drainage canals become blocked or covered.  This causes a sudden rise in eye pressure as fluid production continues.
 
For many people, the exact cause of glaucoma is unknown.  Open-angle and closed- angle glaucoma appears to run in families.  Glaucoma occurs more frequently in adults over the age of 40 and African Americans.  People with diabetes, farsightedness, large cataracts, cataract surgery, and previous eye injuries or infection have an increased risk for glaucoma.  Additionally, long-term corticosteroid use may contribute to the development of glaucoma.

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Symptoms
Open-angle glaucoma is painless.  It may not cause symptoms at first.  Over months or years it may cause blind spots or areas of vision loss.  Peripheral (side) vision is usually lost first.  The central vision is usually lost last, and this contributes to tunnel vision.  People with tunnel vision can see straight ahead, but not in other directions.  If left untreated, open-angle glaucoma can lead to total blindness.
 
Closed-angle glaucoma is a medical emergency.  You should seek emergency care as soon as you experience symptoms because vision loss can result in as short as two or three hours.  Closed-angle glaucoma causes sudden symptoms.  It can cause severe eye pain, severe headache, red eyes, unreactive pupils, nausea, and vomiting.  You may have blurred or cloudy vision or see rainbow halos around lights. 

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Diagnosis
Early detection of glaucoma is very important and should be part of a regular comprehensive eye exam.  There are several methods to test for glaucoma.  A painless tonometer test measures the pressure in your eye.  Your doctor may look at your optic nerve using a slit lamp or scope.  Visual field testing is used to assess your visual field and map areas of vision loss.  Your doctor may view your anterior chamber channels with a gonioscopy, a procedure that uses a slit lamp and hand held lens.  A gonioscopy is used to determine if open-angle or closed-angle glaucoma is present.

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Treatment
The goal of treatment is to prevent and stop the progression of vision loss.  Vision loss from glaucoma cannot be reversed. Early detection and early treatment of glaucoma is vital.

Glaucoma involves lifelong treatment and monitoring.  Most people with open-angle glaucoma respond well to eye drop medications.  Surgery may be necessary if eye drops fail to reduce intraocular pressure.  Laser surgery  is used to open the canals in people with open-angled glaucoma.  Lasers can also be used  to open the iris in people with closed-angle glaucoma.  In some cases, glaucoma filtration surgery called trabeculectomy is used to create a new drainage system for the eye.

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Am I at Risk

People who are farsighted are at greatest risk for angle closure glaucoma.  Open angle glaucoma often runs in families but anybody can develop it.  People who have sleep apnea are also at risk.

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Complications
Some of the medications used to treat glaucoma can cause problems.  Most complications are uncommon but can include slowing of the heart rate, asthma attacks, decreased potassium levels in the body, change in iris color and pigmentation on the conjunctiva.  As with any medication possible side effects should be discussed with your doctor.

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This information is intended for educational and informational purposes only. It should not be used in place of an individual consultation or examination or replace the advice of your health care professional and should not be relied upon to determine diagnosis or course of treatment.

The iHealthSpot patient education library was written collaboratively by the iHealthSpot editorial team which includes Senior Medical Authors Dr. Mary Car-Blanchard, OTD/OTR/L and Valerie K. Clark, and the following editorial advisors: Steve Meadows, MD, Ernie F. Soto, DDS, Ronald J. Glatzer, MD, Jonathan Rosenberg, MD, Christopher M. Nolte, MD, David Applebaum, MD, Jonathan M. Tarrash, MD, and Paula Soto, RN/BSN. This content complies with the HONcode standard for trustworthy health information. The library commenced development on September 1, 2005 with the latest update/addition on April 13th, 2016. For information on iHealthSpot’s other services including medical website design, visit www.iHealthSpot.com.