John Meehan, MD Eye Doctor Dartmouth
John E. Meehan

Glaucoma -  Diagram of the eyeWhat is glaucoma?
Glaucoma is a group of diseases that can damage the eye's optic nerve and result in vision loss and blindness. Glaucoma occurs when the normal fluid pressure inside the eyes slowly rises. However, with early treatment, you can often protect your eyes against serious vision loss.

What is the optic nerve?
The optic nerve is a bundle of more than 1 million nerve fibers. It connects the retina to the brain. The retina is the light-sensitive tissue at the back of the eye. A healthy optic nerve is necessary for good vision.


  1. NarrowAngle Glaucoma (NAG) is a less common type of glaucoma. Although it is curable by laser iridotomy, it is imperative that these patients continue to be monitored, as many of them will also, eventually, develop open angle glaucoma. No drops are used in treating this type of glaucoma. Laser iridotomy, a 60-second procedure is employed to cure narrow angle glaucoma. This procedure has been available for 25 years and can be performed using either the Argon or the YAG laser.

  2. Open Angle Glaucoma (OAG - by far the most common type of glaucoma) is controllable, but not curable. It is a chronic (i.e., forever) and progressive (i.e., it gets worse with age) condition. As such, it must be monitored regularly and retreated throughout life. The new SLT laser, unlike the traditional Argon laser, allows for re-treatment in the future as the glaucoma progresses with age.


Glaucoma - Fluid pathway How does open-angle glaucoma damage the optic nerve?
In the front of the eye is a space called the anterior chamber. A clear fluid flows continuously in and out of the chamber and nourishes nearby tissues. The fluid leaves the chamber at the open angle where the cornea and iris meet. (See diagram below.) When the fluid reaches the angle, it flows through a spongy meshwork, like a drain, and leaves the eye.

Sometimes, when the fluid reaches the angle, it passes too slowly through the meshwork drain. As the fluid builds up, the pressure inside the eye rises to a level that may damage the optic nerve. When the optic nerve is damaged from increased pressure, open-angle glaucoma--and vision loss--may result. That's why controlling pressure inside the eye is important.

Does increased eye pressure mean that I have glaucoma?
Not necessarily. Increased eye pressure means you are at risk for glaucoma, but does not mean you have the disease. A person has glaucoma only if the optic nerve is damaged. If you have increased eye pressure but no damage to the optic nerve, you do not have glaucoma. However, you are at risk. Follow the advice of your eye care professional.

Can I develop glaucoma if I have increased eye pressure?
Not necessarily. Not every person with increased eye pressure will develop glaucoma. Some people can tolerate higher eye pressure better than others. Also, a certain level of eye pressure may be high for one person but normal for another.

Whether you develop glaucoma depends on the level of pressure your optic nerve can tolerate without being damaged. This level is different for each person. That's why a comprehensive dilated eye exam is very important. It can help your eye care professional determine what level of eye pressure is normal for you.

Can I develop glaucoma without an increase in my eye pressure?
Yes. Glaucoma can develop without increased eye pressure. This form of glaucoma is called low-tension or normal-tension glaucoma. It is not as common as open-angle 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.
  • Everyone over age 60, especially Mexican Americans.
  • People with a family history of glaucoma.


A comprehensive dilated eye exam can reveal more risk factors, such as high eye pressure, thinness of the cornea, and abnormal optic nerve anatomy. In some people with certain combinations of these high-risk factors, medicines in the form of eyedrops reduce the risk of developing glaucoma by about half.

Medicare covers an annual comprehensive dilated eye exam for some people at high risk for glaucoma.

What are the symptoms of glaucoma?

At first, there are no symptoms. Vision stays normal, and there is no pain.

However, as the disease progresses, a person with glaucoma may notice his or her side vision gradually failing. That is, objects in front may still be seen clearly, but objects to the side may be missed.

As glaucoma remains untreated, people may miss objects to the side and out of the corner of their eye. Without treatment, people with glaucoma will slowly lose their peripheral (side) vision. They seem to be looking through a tunnel. Over time, straight-ahead vision may decrease until no vision remains.

Glaucoma can develop in one or both eyes.

Glaucoma - Normal vision vs glaucoma vision

How is glaucoma detected?
Glaucoma is detected through a comprehensive eye exam that includes:

  1. Routine Eye Exam- During your routine eye exam your Doctor will look for general signs of glaucoma and record of there is a Family History..
  2. Tonometry-Also performed during your routine eye exam, this test measures the eye pressure.
  3. Visual Field Test-This test measures your side (peripheral) vision. It helps your eye care professional tell if you have lost side vision, a sign of glaucoma.
  4. Dilated eye exam- Drops are placed in your eyes to widen, or dilate, the pupils. Your eye care professional uses a special magnifying lens to examine your retina and optic nerve for signs of damage and other eye problems. After the exam, your close-up vision may remain blurred for several hours.
  5. Pachymetry- A numbing drop is applied to your eye. Your eye care professional uses an ultrasonic wave instrument to measure the thickness of your cornea.

Glaucoma Treatment - eye diagram

  1. Medicines. Medicines, in the form of eyedrops or pills, are the most common early treatment for glaucoma. Some medicines cause the eye to make less fluid. Others lower pressure by helping fluid drain from the eye.

    Before you begin glaucoma treatment, tell your eye care professional about other medicines you may be taking. Sometimes the drops can interfere with the way other medicines work.

    Glaucoma medicines may be taken several times a day. Most people have no problems. However, some medicines can cause headaches or other side effects. For example, drops may cause stinging, burning, and redness in the eyes. Many drugs are available to treat glaucoma. If you have problems with one medicine, tell your eye care professional. Treatment with a different dose or a new drug may be possible.

    Because glaucoma often has no symptoms, people may be tempted to stop taking, or may forget to take, their medicine. You need to use the drops or pills as long as they help control your eye pressure. Regular use is very important. Make sure your eye care professional shows you how to put the drops into your eye.

  2. LASERS: 40 years ago the Argon Laser was introduced, and since that time has remained the mainstay of open angle glaucoma laser treatment. It works by causing microscopic scarring (thermal damage) of few of the honeycombed-like aqueous fluid drains which results in the stretching and opening of adjacent honeycombed drainage channels. This allows the fluid to drain better. Argon laser treatment (ALT) can generally be performed only twice over a number of years: each time treating ½ of the drainage area (trabecular meshwork) which encircles the front of the eye and is located along the base of the iris. Remember that glaucoma is chronic and progressive. As such, the 2nd treatment comes not because the first treated failed, but because, with time, the glaucoma itself becomes worse, more difficult to control, and requires further treatment.
  3. SLT Laser
    Although developed several years ago, the SLT laser has been fine- tuned and improved during the last 10 years. The SLT laser, unlike the ALT, produces essentially no apparent scarring to the honeycombed fluid drainage (trabecular meshwork) system. It works by selectively breaking up intracellular pigment which causes the honeycombed drainage framework to swell and become obstructed. (Remember that it is this obstruction of the microscopic drainage meshwork that causes the elevated pressure characteristic of open angle glaucoma in the first place.) In essence the SLT laser widens and opens the drainage "pores" which have become narrowed and obstructed with age.

    The SLT laser is considered very safe and because it is not associated with permanent scarring of the draining system, it will be replacing the argon laser procedure (ALT) as the primary treatment modality for open angle glaucoma. Unlike its argon laser predecessor, the SLT can be used to treat essentially any patient with open angle glaucoma (OAG): i.e.,

    • newly diagnosed glaucoma patients as an alternative to first starting treatment with eye drops
    • existing glaucoma patients who are using one or more eye drops as a way of decreasing or eliminating the need for drops
    • long-standing chronic glaucoma patients who have already had one or two argon laser (ALT) treatments and thus cannot have any more ALT treatments

    There are only two other facilities in the area capable of providing the SLT laser technology: one in Providence and the other at the Massachusetts Eye and Ear Infirmary in Boston. Appointments with Dr. Sullivan for evaluation as to appropriateness of SLT treatment may be scheduled by calling his office at 508-994-1400 or 508-823-5536.

  4. Conventional Surgery. Glaucoma surgery has been available for over 50 years, but has been reserved as a last resort in patients who are still losing vision despite the use of multiple drops and laser treatments. Glaucoma surgery though successful and often necessary carries a higher risk than the use of either drops or laser.Conventional surgery makes a new opening for the fluid to leave the eye.

    The National Eye Institute (NEI) is part of the National Institutes of Health (NIH) and is the Federal government's lead agency for vision research that leads to sight-saving treatments and plays a key role in reducing visual impairment and blindness.