What is Glaucoma? How Does It Affect the Eye?

What is Glaucoma? How Does It Affect the Eye?

A leading cause of preventable blindness.

To understand our discussions about glaucoma you need to gain an understanding of the anatomy of the eye. The eye is an amazing optical device. The eye focuses the light from the environment, creating an image that is processed and sent to the brain where the image is interpreted. In this way, the eye is very similar to a camera.

The eye is a fluid-filled globe about an inch in diameter. To focus light, the eye needs to maintain a smooth round shape. To keep the eye round, the eye is filled with a fluid called the aqueous, much like the tires on your car are filled with air to keep them round. There is a certain pressure in this aqueous fluid just like your car tire has pressure in the air. Under normal circumstances, the pressure in the eye is between 10 and 20. The fluid is created by a special tissue called the ciliary body. It then circulates through the eye and eventually drains out of the eye at the drainage tissue called the trabecular meshwork.

A visual image is formed when light enters the eye and is focused onto the retina by the clear lens. The retina then changes the image into electrical signals that are sent along one million tiny nerve fibers in the optic nerve. These electrical signals arrive in a special area of the brain where the electrical signals are interpreted.

So how do fluid flow and electrical signals relate to glaucoma? Glaucoma is a disease where the optic nerve and the tiny nerve fibers within it degenerate. A damaged nerve leads to decreased vision and even blindness in advanced cases. The most common cause of the nerve damage (glaucoma damage) is an increased eye pressure. The eye pressure increases when the drain inside the eye (trabecular meshwork) gets clogged and the fluid doesn’t flow through it easily. When the pressure increases, this pushes against the nerve and over many months and years causes the nerve to degenerate.

How Glaucoma Affects The Eye

Each tiny nerve fiber of the optic nerve is responsible for a certain area of vision. Glaucoma damage causes these tiny nerve fibers to degenerate. The loss of a few nerve fibers is completely unnoticeable. This is why mild glaucoma has no symptoms. As more and more nerve fibers are damaged, subtle changes start to develop with certain areas of the vision becoming less clear. Even this is usually so mild that the average person doesn’t notice any changes in their vision. Small changes like this can be detected with a visual field test that measures glaucoma damage in the peripheral vision. With more damage over time you may start to notice trouble seeing things in dim lighting and a general decrease in the quality of the vision. In late stages of the disease severe visual disability and blindness can occur. Glaucoma damage to the nerve fibers is permanent and irreversible. Once areas in the vision are lost they can never be brought back. That is why treatment and close monitoring are so important.

Peter DeBry
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