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Eye Anatomy: The Retina

Eye Anatomy Retina We use our eyes everyday. Some say that the eyes are the windows to the soul, but one could argue that they are also our windows to the world. Without eyes we would be unable to see a beautiful spring flower or the face of a beloved child. Eyesight is truly a gift that we can appreciate and use everyday when we have it and that will be missed everyday if our sight should fade.

The eye is a complex structure that uses several distinct parts to allow us to see. Some of these parts can be easily seen when looking at an eye. For example, you can see the pupil, the iris and even various blood vessels in the eye. However, the eye has many parts that you cannot see when looking at an eye that are just as important. One of these is the retina.

What is the Retina?
The retina is located at the back of the eye. It is comprised of special cells known as rods and cones. These cells capture images which are then relayed to the brain. If we were to compare the retina to a common household object, we might say that it acts similarly to film in a camera. As the cells in the retina capture light, they transform this light into a nerve signal which can be transported to the brain for processing.

Rods and Cones
Rods and cones are the special light sensitive cells inside of the retina. Both serve a different, but important, purpose in the eye. Each eye has between 6 and 7 million cones. The cones are responsible for vision when we have light. They help us to see and recognize colors. We also have between 75 and 150 million rods. These are responsible for helping us to see in dim light. Rods are better able to react to the light which enables us to see when there isnít as much light available. Proper vision requires both rods and cones since each fulfills a distinct purpose in our ability to see.

The Macula
As we mentioned before, the retina is located at the back of the eye. It is about .5mm thick. The exterior wall of the eye is comprised of 3 distinct layers, with the retina located on the layer closest to the inside of the eye. In the center of the retina you will find a part of the eye known as the macula.

Rods and cones are dispersed throughout the retina unevenly. This greatly impacts your vision. The rods are typically found around the edges of the retina, also known as retinal periphery, while the cones tend to be clustered in or near the macula. This helps the macula to provide clear vision directly in front of the eyes.

How Does the Retina Help You to See?
While the retina captures images, it cannot do this alone. It relies on the other parts within the eye to provide vision. As you look at object, light will enter your eye. Then the lens will focus this light onto the back of the eye or the retina. When this happens your rods and cones are able to get to work. Since rods and cones are light sensitive they can take the light passing through your eye and create an image. This image is translated into a nerve signal. Rods and cones are all attached to various nerve fibers. The many nerve fibers found in the eye all come together near the macula where they form what we call the optic nerve. The optic nerve will act as a highway for the retina and will transport the nerve signal that is created to the brain.

Problems with the Retina
As with many parts of the eye, problems can arise in the retina. Sometimes these problems can result in serious vision problems. One problem is known as retinal detachment. This occurs when the retina detaches from its blood supply. If this happens the cells in the retina will start to die and this can result in permanent blindness if it not treated quickly.

Another common retina problem is macular degeneration. This eye disease is currently incurable and is the leading cause of blindness for those over the age of 55 in the United States. Those with macular degeneration experience deterioration of their macula. Since this is responsible for providing sharp central vision it can seriously impact eyesight.

Electroretinography (ERG)
One of the most common tests used to diagnose problems with the retina is electroretinography or ERG. This test can be used to determine if the cells in the retina are functioning properly. During the test a special electrode is attached to the cornea, or front of the eye. Then the rods and the cones within the eye are then examined. The electrode can measure the response of the retinal cells to light. This test can help to diagnose various problems with the retina so that treatment options can be considered.

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