In chronic glaucoma, the circulation of a fluid called aqueous humor, which is produced constantly by the ciliary body in the eye, is blocked gradually over a period of years. Aqueous humor builds up in the eye, and eventually creates an internal pressure that affects the blood supply to the retina and the optic nerve, both of which are essential to vision. The aqueous humor normally drains out of the eye through a network of tissue between the iris and the cornea. This network is called the drainage angle, and it is there that the blockage occurs.

As the disorder progresses, it becomes increasingly more difficult for the aqueous humor (which normally flows from behind the iris, through the pupil, and into the chamber between the iris and the cornea) to drain out of the eye through the drainage angle. The blockage causes a slow and steady build-up of internal pressure on the rest of the eyeball. For a more detailed description of how glaucoma occurs, read the introduction to this section .

Unlike acute glaucoma (see previous article), chronic glaucoma often is not detected without an eye examination. This is because the blockage occurs and the pressure builds up so slowly. In most cases of chronic glaucoma, both eyes are affected by the disorder, one soon after the other.

What are the symptoms?

The development of the disorder is so gradual that the only symptom that occurs in the early stages is too slight to be noticeable. This is the loss of small areas of peripheral vision in one eye, on the side near the nose, caused by pressure in the eyeball that damages the fibers of the optic nerve. The loss passes unnoticed because the peripheral vision of the other eye compensates for it. Gradually, other areas of peripheral vision are lost, the areas lost increase in size, and the disorder affects the other eye. At some point in this process, you will become aware of the loss of part of your vision.

What are the risks?

Chronic glaucoma is more common than acute glaucoma . It may affect one to two per cent of the population over the age of 40. The risk increases from middle age onwards. The disease tends to run in families, so you are more likely to get it if you have relatives who have it.

If the disease is allowed to continue unchecked, all your peripheral vision in both eyes is lost. Then the ability of the eye to see straight ahead gradually diminishes until it disappears altogether and both eyes become totally blind.

What should be done?

Since any vision that is lost through the disease cannot be regained, the sooner you receive treatment the better. In the early stages of this type of glaucoma, it is impossible to tell that you have it unless you are tested for it. For this and other good reasons, you should have regular eye examinations by a qualified physician. Be sure to go to an ophthalmologist for a checkup every two to three years after you reach the age of 40.

What is the treatment?

The treatment for chronic glaucoma is to try to bring down the pressure in the eyeball as quickly as possible. You will probably be given eye drops that partially unblock the drainage angles and/or drops or tablets to reduce the production of aqueous humor. All these drops and tablets generally have to be taken for life, and you will also need to have regular checkups by your physician to be certain that all is going well. Taking the drugs soon becomes part of your daily routine, and if you continue to take them you should not have any further loss of vision.

If drugs fail to reduce the pressure in the eye sufficiently, the ophthalmologist will probably recommend that you have an operation in which the surgeon creates an artificial drainage channel. This procedure has a high rate of success.