Glaucoma - Introduction

Primary Open-Angle Glaucoma

Most people with glaucoma have the form called primary-open-angle glaucoma (also called chronic open-angle glaucoma). Open-angle glaucoma is essentially a plumbing problem.

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The disease process may occur as follows:

The drainage angle remains open, but tiny drainage channels in the trabecular meshwork pathway become clogged. This pathway is responsible for most aqueous humor fluid outflow. An imbalance then occurs as fluid continues to be produced but does not drain out efficiently. Experts have still not definitely determined the precise area in the pathway where the blockage is most likely to occur. (In rare instances the pressure is high because the eye produces too much aqueous humor.)
The fluid in the eye?s anterior chamber builds up and increases pressure within the eye. This is called intraocular pressure (IOP).
The intraocular pressure exerts force on the optic nerve at the back of the eye.
Over time, the persistent pressure or other factors irreversibly damages the delicate long fibers of the optic nerve, called axons, which convey images to the brain.
As these axons die, the small cup-like head of the optic nerve may eventually collapse into an enlarged irregular shape.

Optic nerve damage is the basic glaucoma condition. If it is untreated, eventually the nerve deteriorates until a person loses sight, first in the peripheral vision (the vision in the "corner of the eyes"). If it becomes severe, the person loses central vision (in the middle of the eyes), and may eventually become blind. (Blindness is fortunately nearly always preventable with early treatment.)

Primary open-angle glaucoma tends to start in one eye but eventually involves both. In about half of patients the damage in the eye is diffuse, that is the nerve damage is generalized. In the other half the disease is localized, causing wedge-shaped abnormalities in the nerve fiber layers of the retina.

Normal Tension Glaucoma

Intraocular eye pressure is normal (between 12 and 22 mmHg) in about 25 - 30% of U.S. glaucoma cases, a condition known as normal tension glaucoma. (In Japan, the rates may be as high as 70%.) Other factors are present then that cause optic nerve damage but do not affect IOP.

Closed-Angle Glaucoma

Closed-angle glaucoma (also called angle-closure glaucoma) is responsible for 15% of all cases. It is less common than open-angle glaucoma in the U.S., but it constitutes about half of the world's glaucoma cases because of its higher prevalence in Asians. The iris is pushed against the lens, sometimes sticking to it, closing off the drainage angle. This can occur very suddenly, resulting in an immediate rise in pressure. It often occurs in genetically susceptible people when the pupil shrinks suddenly. Closed-angle glaucoma can also be chronic and gradual, a less common condition.