What is Glaucoma?
Glaucoma is a disease that damages your eye's optic nerve. It usually happens when fluid builds up in the front part of your eye. That extra fluid increases the pressure in your eye, damaging the optic nerve.
Types of Glaucoma
Open Angle Glaucoma
The most common form of glaucoma is called primary open-angle glaucoma. It occurs when the trabecular meshwork of the eye gradually becomes less efficient at draining fluid. As this happens, your eye pressure, called intraocular pressure (IOP), rises. Raised eye pressure leads to damage of the optic nerve. Damage to the optic nerve can occur at different eye pressures in different patients. There is not one ‘right’ eye pressure that is the same for everyone. Your ophthalmologist or optometrist 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.
Typically, open-angle glaucoma has no symptoms in its early stages and your vision remains normal. As the optic nerve becomes more damaged, blank spots begin to appear in your field of vision. You usually won’t notice these blank spots in your day-to-day activities until the optic nerve is significantly damaged and these spots become large. If all of the optic nerve fibers die, you will be blind.
Half of patients with glaucoma do not have high eye pressure when first examined. Eye pressure is not always the same – it rises and falls from day to day and hour to hour. So a single eye pressure test will miss many people who have glaucoma. In addition to routine eye pressure testing, it is essential that the optic nerve be examined by an ophthalmologist for proper diagnosis.
Eye pressure is expressed in millimeters of mercury (mmHg), the same unit of measurement used in weather barometers.
Although "normal" eye pressure is considered a measurement less than 21 mmHg, this can be misleading. Some people have a type of glaucoma called normal-tension, or low-tension glaucoma. Their eye pressure is consistently below 21 mmHg, but optic nerve damage and loss of vision still occur. People with normal-tension glaucoma are usually treated in the same way as people who have open-angle glaucoma.
Angle-closure glaucoma (also called "closed-angle glaucoma" or "narrow-angle glaucoma")
This type happens when someone’s iris is very close to the drainage angle in their eye. The iris can end up blocking the drainage angle. You can think of it like a piece of paper sliding over a sink drain. When the drainage angle gets completely blocked, eye pressure rises very quickly. This is called an acute attack. It is a true eye emergency, and you should call your ophthalmologist right away or you might go blind. People of Asian descent and those with hyperopia (farsightedness) tend to be more at risk for developing this form of glaucoma.
Symptoms of an acute attack include:
- Your vision is suddenly blurry
- You have severe eye pain
- You have a headache
- You feel sick to your stomach (nausea)
- You throw up (vomit)
- You see rainbow-colored rings or halos around lights
A closed-angle glaucoma attack is a medical emergency and must be treated immediately. Unfortunately, people at risk for developing closed-angle glaucoma often have few or no symptoms before the attack.
People at risk for closed-angle glaucoma should avoid over-the-counter decongestants and other medications where the packaging states not to use these products if you have glaucoma. These products are usually safe to use once your narrow angle has been treated with laser iridotomy. Always ask your ophthalmologist if it is safe for you to use products with this warning.
Congenital glaucoma is a rare type of glaucoma that develops in infants and young children and can be inherited. While less common than the other types of glaucoma, this condition can be devastating, often resulting in blindness if not diagnosed and treated early.
Secondary glaucoma is glaucoma that results from another eye condition or disease. For example, someone who has had an eye injury, someone who is on long-term steroid therapy or someone who has a tumor may develop secondary glaucoma. The most common forms of secondary glaucoma are: pseudoexfoliative glaucoma, pigmentary glaucoma, and neovascular glaucoma.
Some people have normal eye pressure but their optic nerve or visual field looks suspicious for glaucoma. These people must be watched carefully because some eventually develop definite glaucoma and need treatment.
Other people have an eye pressure that is higher than normal, but they do not have other signs of glaucoma, such as optic nerve damage or blank spots that show up in their peripheral (side) vision when tested. This condition is called ocular hypertension. Individuals with ocular hypertension are at higher risk for developing glaucoma compared to people with lower, or average, eye pressure. Just like people with glaucoma, people with ocular hypertension need to be closely monitored by an ophthalmologist to ensure they receive appropriate treatment.
Symptoms of glaucoma
In its early stages, open-angle glaucoma has no obvious symptoms. As the disease progresses more blind spots develop in the peripheral (side) view. These points can go undetected until the optic nerve has had serious damage, or until it is detected by an ophthalmologist through a complete eye exam.
People at risk for angle closure glaucoma (also called narrow angle glaucoma), usually show no symptoms before an attack. Some early symptoms may include blurred vision, halos, mild headaches or eye pain. An attack of angle-closure glaucoma includes the following:
- Severe pain in the eye or forehead
- Redness of the eye
- Decreased vision or blurred vision
- Vision rainbows or halos
People with "normal tension glaucoma" can have their eye pressure within normal ranges, but show signs and symptoms of glaucoma, such as blind spots in their field of vision and optic nerve damage.
Some people may not have symptoms of glaucoma, but may have a higher than normal eye pressure (called ocular hypertension). These patients are considered as "glaucoma suspects," and should be carefully evaluated by an ophthalmologist.
The only sure way to diagnose glaucoma is with a complete eye exam. A glaucoma screening that only checks eye pressure is not enough to find glaucoma.
One of the problems with glaucoma, especially open-angle glaucoma, is that there are typically no symptoms in the early stages. Many people who have the disease do not know they have it. This is why it is important, especially as you get older, to have regular medical eye exams by an Eye M.D.
Your ophthalmologist will do the following tests and exams during a comprehensive glaucoma evaluation:
Measure the pressure in your eye (tonometry)
Your doctor measures your eye pressure using tonometry. (See photo above) Testing your eye pressure is an important part of a glaucoma evaluation. A high pressure reading is often the first sign that you have glaucoma. During this test, your eye is numbed with eye drops. Your doctor uses an instrument called a tonometer to measure eye pressure. The instrument measures how your cornea resists pressure. Normal eye pressure generally ranges between 10 and 21 mmHg. However, people with normal-tension glaucoma can have damage to their optic nerve and visual field loss even though their eye pressure remains consistently lower than 21 mmHg.
Inspect your eye’s drainage angle (gonioscopy)
Gonioscopy allows your ophthalmologist to get a clear look at the drainage angle to determine the type of glaucoma you may have. Your ophthalmologist is not able to see your eye’s drainage angle by looking at the front of your eye. However, by using a mirrored lens, he or she can examine the drainage angle to determine if you have open-angle glaucoma (where the drainage angle is not working efficiently enough), closed-angle glaucoma (where the drainage angle is at least partially blocked), or a dangerously narrow angle (where the iris is so close to the eye’s drain that the iris could block it).
Inspect your optic nerve (ophthalmoscopy)
Your ophthalmologist inspects your optic nerve for signs of damage using an ophthalmoscope, an instrument that magnifies the interior of the eye. Your pupils will be dilated (enlarged) with eye drops to allow your doctor a better view of your optic nerve.
A normal optic nerve is made up of more than one million tiny nerve fibers. As glaucoma damages the optic nerve, it causes the death of some of these nerve fibers. As a result, the appearance of the optic nerve changes. This is referred to as cupping. As the cupping increases, blank spots begin to develop in your field of vision.
Test your side, or peripheral, vision (visual field test)
The visual field test will check for blank spots in your vision. The results of the test show your ophthalmologist if and where blank spots appear in your field of vision — including spots you may not even notice.
The test is performed using a bowl-shaped instrument called a perimeter. When taking the test, a patch is temporarily placed on one of your eyes so that only one eye is tested at a time. You will be seated and asked to look straight ahead at a target. The computer makes a noise and random points of light will flash around the bowl-shaped perimeter, and you will be asked to press a button whenever you see a light with your side vision. You should not turn your eyes to look for the lights. Not every noise is followed by a flash of light. Visual field testing is usually performed every 6 to 12 months to monitor for change.
Measure the thickness of your cornea — the clear window at the front of the eye (pachymetry)
Because the thickness of the cornea can affect eye pressure readings, pachymetry is used to measure corneal thickness. A probe called a pachymeter is gently placed on the cornea to measure its thickness. A very thin cornea may increase your risk of glaucoma.
How your glaucoma is treated will depend on your specific type of glaucoma, the severity of your disease and how well it responds to treatment.
A surgery called laser trabeculoplasty is often used to treat open-angle glaucoma. There are two types of trabeculoplasty surgery: argon laser trabeculoplasty (ALT) and selective laser trabeculoplasty (SLT).
During ALT surgery, a laser makes tiny, evenly spaced burns in the trabecular meshwork. The laser does not create new drainage holes, but rather stimulates the drain to work better.
SLT uses a newer, lower-energy laser which only treats specific cells in the drainage angle. SLT and ALT are equally good at lowering eye pressure.
Even if laser trabeculoplasty is successful, many patients continue taking glaucoma medications after surgery. For many, this surgery is not a permanent solution. Nearly half of the people who receive this surgery develop increased eye pressure again within five years. Many people who have had a successful laser trabeculoplasty will need more treatment in the future. This treatment may be another laser, more medication or surgery.
Laser trabeculoplasty is commonly used as a first line of treatment for patients.
Medicated eye drops are a common way to treat glaucoma. These medications lower your eye pressure in one of two ways — either by reducing the amount of fluid created in the eye or by helping this fluid flow out of the eye 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.
Once you are taking medications for glaucoma, your ophthalmologist will want to see you regularly.
You can expect to visit your ophthalmologist about every 3–6 months. However, this can vary depending on your treatment needs.
If you have any questions about your eyes or your treatment, talk to your ophthalmologist.
In some patients with glaucoma, surgery is recommended. Glaucoma surgery improves the flow of fluid out of the eye, resulting in lower eye pressure.
Laser iridotomy is recommended for treating people with closed-angle glaucoma and those with very narrow drainage angles. A laser creates a small hole about the size of a pinhead through the iris to improve the flow of aqueous fluid to the drainage angle.
When laser iridotomy is unable to stop an acute closed-angle glaucoma attack, or is not possible for other reasons, a peripheral iridectomy may be performed. This is performed in an operating room. A small piece of the iris is removed, giving the aqueous fluid access to the drainage angle again. Because most cases of closed-angle glaucoma can be treated with glaucoma medications and laser iridotomy, peripheral iridectomy is rarely necessary.
In trabeculectomy, a small flap is made in the sclera (the outer white coating of your eye). A filtration bleb, or reservoir, is created under the conjunctiva — the thin, filmy membrane that covers the white part of your eye. Once created, the bleb looks like a bump or blister on the white part of the eye above the iris, but the upper eyelid usually covers it. The aqueous humor can now drain through the flap made in the sclera and collect in the bleb, where the fluid will be absorbed into blood vessels around the eye.
Eye pressure is effectively controlled in three out of four people who have trabeculectomy. Although regular follow-up visits with your doctor are still necessary, many patients no longer need to use eye drops. If the new drainage channel closes or too much fluid begins to drain from the eye, additional surgery may be needed.
Aqueous shunt surgery
If trabeculectomy cannot be performed, aqueous shunt surgery is usually successful in lowering eye pressure.
An aqueous shunt, or glaucoma drainage device, is a small plastic tube or valve connected to a reservoir (a roundish or oval plate). The plate is placed on the outside of the eye beneath the conjunctiva (the thin membrane that covers the inside of your eyelids and the white part of your eye). The tube is placed into the eye through a tiny incision and allows aqueous humor to flow through the tube to the plate. The fluid is then absorbed into the blood vessels. When healed, the reservoir is not easily seen unless you look downward and lift your eyelid.
Important things to remember about glaucoma treatment
There are a number of ways to treat glaucoma. While some people may experience side effects from glaucoma medications or glaucoma surgery, the risks of side effects should always be balanced with the greater risk of leaving glaucoma untreated and losing vision
If you have glaucoma, preserving your vision requires strong teamwork between you and your doctor. Your doctor can prescribe treatment, but it’s important to do your part by following your treatment plan closely. Be sure to take your medications as prescribed and see your ophthalmologist regularly.
From the American Academy of Ophthalmology