What is Glaucoma?
Glaucoma is a disease that damages the eye’s optic nerve. The optic nerve is connected to the retina — a layer of light-sensitive tissue lining the back of the eye — and is made up of many nerve fibers, like an electric cable is made up of many wires. It is the optic nerve that sends signals from your retina to your brain, where these signals are interpreted as the images you see.
In the healthy eye, a clear fluid called aqueous (pronounced AY-kwee-us) humor circulates inside the front portion of your eye. To maintain a constant healthy eye pressure, your eye continually produces a small amount of aqueous humor while an equal amount of this fluid flows out of your eye. If you have glaucoma, the aqueous humor does not flow out of the eye properly. Fluid pressure in the eye builds up and, over time, causes damage to the optic nerve fibers.
Glaucoma can cause blindness if it is left untreated. Only about half of the estimated three million Americans who have glaucoma are even aware that they have the condition. When glaucoma develops, usually you don’t have any early symptoms and the disease progresses slowly. In this way, glaucoma can steal your sight very gradually. Fortunately, early detection and treatment (with glaucoma eyedrops, glaucoma surgery or both) can help preserve your vision.
Causes of Glaucoma
Glaucoma causes include elevated eye pressure (called intraocular pressure or IOP) due to the eye’s inability to drain fluid efficiently.
A clear fluid called aqueous humor circulates inside the front portion of our eyes. To maintain a constant healthy eye pressure, the eye continually produces a small amount of aqueous humor while an equal amount of this fluid flows out of the
eye. The fluid flows out through a very tiny drain called the trabecular meshwork, a complex network of cells and tissue in an area called the drainage angle.
Damage to the optic nerve can occur at different eye pressures among different patients. Your ophthalmologist establishes a target eye pressure for you that he or she predicts will protect your optic nerve from further damage. Different patients have different target pressures.
Some people have a type of glaucoma called normal tension, or low tension glaucoma. Their eye pressure is consistently below 21 mm Hg, but optic nerve damage and visual field loss still occur.
Congenital glaucoma is a rare type of glaucoma that develops in infants and young children. It can be hereditary, and it happens when the eye’s drainage system doesn’t develop fully or correctly before birth.
Glaucoma can often be caused by another eye condition or disease. This is known as secondary glaucoma. For example, someone who has a tumor or people undergoing long-term steroid therapy may develop secondary glaucoma. Other causes of secondary glaucoma include:
- Eye injury;
- Inflammation of the eye;
- Abnormal blood vessel formation from diabetes or retinal blood vessel blockage;
- Use of steroid-containing medications (pills, eyedrops, sprays); or
- Pigment dispersion, where tiny fragments or granules from the iris (the colored part of the eye) can circulate in the aqueous humor (the fluid within the front portion of the eye) and block the trabecular meshwork, the tiny drain for the eye’s aqueous humor.
Medicated eyedrops are the most common way to treat glaucoma. These medications lower your eye pressure in one of two ways — either by slowing the production of aqueous humor or by improving the flow through the drainage angle.
These eyedrops must be taken every day. Just like any other medication, it is important to take your eyedrops regularly as prescribed by your ophthalmologist.
If you have glaucoma, it is important to tell your ophthalmologist about your other medical conditions and all other medications you currently take. Bring a list of your medications with you to your eye appointment. Also tell your primary care doctor and any other doctors caring for you what glaucoma medication you take.
In some patients with glaucoma, surgery is recommended. Glaucoma surgery improves the flow of fluid out of the eye, resulting in lower eye pressure.
Visual field loss
Progressive loss of the optic nerve fibers leads eventually to progressive loss of visual field and finally to complete loss or blindness. However, in most forms of glaucoma, a patient will not experience any symptoms until late in the disease. Early peripheral visual field loss is not noticeable to the patient, and its slow progression makes its recognition nearly impossible without special testing. In its normal physiologic state, greater than one million fibers of the optic nerve carry visual information from retinal ganglion cells through the nerve fiber layer of the retina, along the optic nerve, and to the brain. Fortunately, there is a certain amount of functional reserve in the optic nerve so that a considerable portion, perhaps even half, of the nerve fibers can be lost before significant visual field loss occurs. This offers the opportunity for early diagnosis of disk changes before significant visual loss transpires. The functional status of the optic nerve can be assessed by specialized testing of the peripheral vision, the “visual field.”
The special anatomy of the nerve fiber layer in the retina produces visual field defects from glaucoma that follow a characteristic pattern. Visual field loss in glaucoma usually arches from the physiologic blind spot of the optic disk, curves around the central region, and ends abruptly along the horizontal axis nasally. These arch-shaped defects are referred to as “Bjerrum,” or arcuate, scotomas. Loss of the peripheral nasal visual field generally occurs first in glaucoma. Following the progressive change and course of these visual field defects becomes the most critical aspect of managing the glaucoma patient. Source: American Glaucoma Society.
How often should a person with glaucoma see an ophthalmologist?
After the initial examination and diagnosis, glaucoma patients are managed much like patients with other chronic disease, requiring regular visits to assess disease severity and response to therapy. The primary criterion for disease status is the visual field, since it is the most accurate measure of visual function in this disorder. Most patients will need periodic medical examinations, diagnostic testing for progression or new findings, and individualized management with drugs or procedures. Once the diagnosis and treatment regimen are established, the average patient needs to be seen 3-4 times yearly. Frequency of visits and testing depends upon risks for progressive damage and severity of illness, as tabulated below. Because performance on visual field testing shows some variability, visual field tests may have to be repeated if they show any changes. Source: American Glaucoma Society.