By Dr Jagriti Jain, MS (Ophthalmology)
Glaucoma is the leading cause of blindness in African-Americans. Globally, it is the second leading cause of blindness, affecting 6.7 million people in 2000. More than 65 million people worldwide have glaucoma and unfortunately, only half of them know that they have it because there are usually no early symptoms associated with this condition. That is the reason it is also known as a silent thief of vision.
What is glaucoma?
Glaucoma refers to a group of eye conditions that lead to damage to the optic nerve, the nerve that carries visual information from the eye to the brain.
In many cases, damage to the optic nerve is due to increased pressure in the eye, also known as intraocular pressure (IOP).
The front part of the eye is filled with a clear fluid called aqueous humor. This fluid is always being made in the back of the eye. It leaves the eye through channels in the front of the eye in an area called the anterior chamber angle, or simply the angle.
Anything that slows or blocks the flow of this fluid out of the eye will cause pressure to build up in the eye. This pressure is called intraocular pressure (IOP). In most cases of glaucoma, this pressure is high and causes damage to the major nerve in the eye, called the optic nerve.
The major types of glaucoma are:
● Open-angle (chronic) glaucoma
● Angle-closure (acute) glaucoma
● Congenital glaucoma
● Secondary glaucoma
Open-angle (chronic) glaucoma is the most common type of glaucoma. An increase in eye pressure occurs slowly over time. It tends to run in families. Your risk is higher if you have a parent or grandparent with open-angle glaucoma.
Angle-closure (acute) glaucoma occurs when the exit of the aqueous humor fluid is suddenly blocked. This causes a quick, severe, and painful rise in the pressure within the eye. If you have had acute glaucoma in one eye, you are at risk for an attack in the second eye, and your doctor is likely to recommend preventive treatment.
Congenital glaucoma is present at birth and it results from the abnormal development of the fluid outflow channels in the eye.
Secondary glaucoma is caused by drugs such as corticosteroids, eye diseases such as uveitis or systemic diseases.
Some other forms of glaucoma known as low-tension or normal-tension glaucoma also occur. In this type optic nerve damage and narrowed side vision occur in people with normal eye pressure. A comprehensive medical history is important in identifying other potential risk factors, such as low blood pressure, that contribute to low-tension glaucoma.
Who is at risk for glaucoma?
Anyone can develop glaucoma. Some people are at higher risk than others. They include:
● African-Americans over age 40.
● People with a family history of glaucoma.
● History of steroid use.
A comprehensive dilated eye exam can reveal more risk factors, such as high eye pressure, thinness of the cornea, and abnormal optic nerve anatomy.
What are the symptoms of glaucoma?
Open-angle glaucoma is a chronic condition that slowly progresses over many years. In its earliest stages, it produces no pain, visual changes, or other symptoms. As the condition progresses and the optic nerve becomes damaged, peripheral vision (vision from the side of the eyes) gradually decreases. Patients develop ‘tunnel vision,’ the ability to only see straight ahead. Eventually, straight-ahead vision decreases and if left untreated, blindness results. These symptoms appear in either one or both eyes.
In acute closed-angle glaucoma, the pressure inside the eye increases quickly, and the symptoms are dramatic. Intense pain in the eyebrow area and blurred vision develop usually in one eye, and the patient often feels like the eye will burst (although it won’t). The eye usually reddens. A person may see rainbow-like halos around lights. Sometimes nausea and vomiting occur. These symptoms may occur on and off and not appear as a full attack. In either case, they indicate a medical emergency. In chronic closed-angle glaucoma, the process is gradual and painless.
Diagnosis
The three tests for glaucoma are outlined below.
An eye pressure test (tonometry)
An optic disc appearance test (ophthalmoscopy) to check for damage in the optic nerve
A visual field test (perimetry) which checks for missing areas of vision
It is very important to have regular eye tests so that problems like this can be detected and treated as early as possible. The American Academy of Ophthalmology strongly supports glaucoma screening, with the following specific recommendations:
● Everyone over age 65 and African-Americans over 40 years old should have periodic eye exams, including tests for glaucoma, every other year.
● African-Americans aged 20-39 should have eye examinations every 3-5 years.
● Other people at higher risk (people with diabetes, a history of eye injuries, a family history of glaucoma, or those taking corticosteroid medications) should have eye examinations every year after age 35.
● People with known glaucoma should have frequent examinations to check peripheral vision and to be sure treatment is maintaining a safe eye pressure. After such examinations, the ophthalmologist will assess current treatment and make necessary adjustments.
How is glaucoma treated?
Glaucoma cannot be cured, but treatment may help delay disease progression. Most treatments for glaucoma aim to reduce ocular pressure and its fluctuations. Early treatment with medications, surgery, or both can nearly always maintain safe pressure of the aqueous humor, thus preventing optic nerve damage and blindness. A number of effective drugs are used to treat glaucoma. The drugs reduce pressure in the eye but they have some side effects that affect other parts of the body. Some of these side effects can be quite severe. Doctors generally recommend topical drugs (such as eye drops) first.
The goal of standard glaucoma surgery is to reduce pressure in the eye by increasing the outflow of the aqueous fluid. Two methods are commonly used: Filtration surgery (trabeculectomy) which uses standard surgical instruments to open a passage in the eye for draining fluid; and laser trabeculoplasty, a procedure which uses a laser to burn tiny holes in the drainage area.
Avoiding the progression of glaucoma
Most of the risk factors such as age, race, and genetics for glaucoma are beyond your control. However, because most people with glaucoma have no early symptoms or pain from this increased pressure, it is important to see your eye care professional regularly so that glaucoma can be diagnosed and treated before long-term vision loss occurs. If there is a history of glaucoma in your family or if you have other risk factors for glaucoma, talk with your health professional about having more frequent exams.