Glaucoma is a group of eye diseases causing optic nerve damage. The optic nerve carries images from the retina, which is the specialized light sensing tissue, to the brain so we can see. In glaucoma, eye pressure plays a role in damaging the delicate nerve fibers of the optic nerve. When a significant number of nerve fibers are damaged, blind spots develop in the field of vision. Once nerve damage and visual loss occur, it is permanent. Most people don’t notice these blind areas until much of the optic nerve damage has already occurred. If the entire nerve is destroyed, blindness results. Glaucoma is a leading cause of blindness in the world, especially in older people. Early detection and treatment by your ophthalmologist are the keys to preventing optic nerve damage and vision loss from glaucoma.
What Causes Glaucoma?
The exact causes of optic nerve damage from glaucoma is not fully understood, but involves mechanical compression and/or decreased blood flow of the optic nerve. Although high eye pressure sometimes leads to glaucoma, many people can also develop glaucoma with “normal” eye pressure.
What are the Different Types of Glaucoma?
Open-angle glaucoma
Chronic open-angle glaucoma is the most common form of glaucoma. The “open” drainage angle of the eye can become blocked leading to gradual increased eye pressure. If this increased pressure results in optic nerve damage, it is known as chronic open-angle glaucoma. The optic nerve damage and vision loss usually occurs so gradually and painlessly that you are not aware of trouble until the optic nerve is already badly damaged.
Angle-closure glaucoma
Angle-closure glaucoma results when the drainage angle of the eye narrows and becomes completely blocked. In the eye, the iris may close off the drainage angle and cause a dangerously high eye pressure. When the drainage angle of the eye suddenly becomes completely blocked, pressure builds up rapidly, and this is called acute angle-closure glaucoma. The symptoms include severe eye pain, blurred vision, headache, rainbow haloes around lights, nausea and vomiting. Unless an ophthalmologist treats acute angle-closure glaucoma quickly, blindness can result. When the drainage angle of the eye gradually becomes completely blocked, pressure builds up gradually, and this is called chronic angle-closure glaucoma. This form of glaucoma occurs more frequently in people of African and Asian ancestry, and in certain eye conditions.
Other Types of Glaucoma
Not all types of glaucoma are characterized by eye pressures. In normal-tension or low-tension glaucoma, the optic nerve suffers damage with the resulting visual field loss even though normal eye pressures are maintained. Eyes afflicted with this condition are far more susceptible to optic nerve damage with any increase in the intraocular pressure compared to other eyes.
Exfoliation syndrome is a common form of open-angle glaucoma that results when there is a buildup of abnormal, whitish material on the lens and drainage angle of the eye. This material and pigment from the back of the iris can clog the drainage system of the eye, causing increased eye pressure. This form of glaucoma responds well to laser treatment.
Pigmentary glaucoma is a condition that typically affects young, nearsighted, Caucasian males. This condition is characterized by the iris bowing backwards, and coming into contact with the support structures that hold the lens in place. This position disrupts the cells lining the back surface of the iris containing pigment, and results in a release of pigment particles into the drainage system of the eye. This pigment can clog the drain and can lead to an increase in eye pressure. This form of glaucoma responds well to laser treatment.
Other types of glaucoma may be caused by injuries to the eye, tumors, and other eye diseases. A rare type of glaucoma can even be present in children at birth.
What are the Warning Signs
Unfortunately, most cases of glaucoma do not occur with readily noticeable symptoms that warn of the irreversible optic nerve damage being done. However, the presence of the following warning signs, indicates that you need a thorough examination by an eye doctor:
- Unusual trouble adjusting to dark rooms
- Difficulty focusing on near or distant objects
- Squinting or blinking due to unusual sensitivity to light or glare
- Change in color of iris
- Red-rimmed, encrusted or swollen lids
- Recurrent pain in or around eyes
- Double vision
- Dark spot at the center of viewing
- Lines and edges appear distorted or wavy
- Excess tearing or “watery eyes”
- Dry eyes with itching or burning; and
- Seeing spots, ghost-like images
The following may be indications of potentially serious problems that might require emergency medical attention:
- Sudden loss of vision in one eye
- Sudden hazy or blurred vision
- Flashes of light or black spots
- Halos or rainbows around light
The symptoms listed above may not necessarily mean that you have glaucoma. However, if you experience one or more of these symptoms, contact your eye doctor for a complete exam.
How Is Glaucoma Detected?
Regular eye examinations by your ophthalmologist are the best way to detect glaucoma. Your ophthalmologist will measure your eye pressure (tonometry); inspect the drainage angle of your eye (gonioscopy); evaluate your optic nerve (ophthalmoscopy); and test the visual field of each eye (perimetry). Optic nerve evaluation and visual field testing are performed at regular intervals to monitor the effects of glaucoma. The information from these tests provides an indication of the effectiveness of the treatment being used and whether further treatments may be necessary. Not all of these tests are necessary for every person, nor at every visit. The objective is to determine if glaucoma damage has progressed over time.
Who is at Risk for Glaucoma?
High eye pressure alone does not mean that you have glaucoma, but it is an important risk factor your ophthalmologist will use to determine your risk for developing the disease.
The most important risk factors include:
- age
- elevated eye pressure
- African ancestry
- thin cornea
- family history of glaucoma
- nearsightedness
- past injuries to the eyes
- steroid use
- a history of severe anemia or shock
Your ophthalmologist will weigh all of these factors before deciding if you need treatment for glaucoma; or whether you should be monitored regularly as a glaucoma suspect to detect the early signs of damage to the optic nerve.