How Eyes Function

Parts of the Human Eye To understand vision, one needs to understand something about how the eye works. The eye is composed of several parts that work together to create sight. It is divided into two main parts; the anterior segment or front of the eye, and the posterior segment or back of the eye.

The main component of the posterior segment is the retina. This is what reacts to light coming into the eye and sends signals to the brain that are interpreted as sight. But if the light doesn't reach the retina properly, vision is affected.

Left Eye That brings us to the front of the eye. It's two important parts are the cornea and lens. These are basically two lenses that focus the light coming into the eye so that it strikes the retina in the proper way for sharp vision. When one of these components changes, for whatever reason, the light no longer reaches the retina in focus...and a visual problem results.

This is called "refractive error" because it is the "refraction" or bending of light that is incorrect as it passes through the cornea and lens. When this occurs, the light needs to be refocused by glasses, contact lenses or surgical treatments, so that is reaches the retina at the right point.


Common Refractive Eye Problems

Nearsighted Eye When near objects are clear, and distant objects blurry, it is called Myopia or "Nearsightedness". This term indicates that the eyes naturally focus light too quickly. Instead of focusing images on the retina, the image comes to focus in front of the retina. This results in blurred vision for distant objects. The shape of the eye and cornea is usually to blame.

Farsighted Eye When distant objects are sharp, and close objects blurry it is called, Hyperopia or "Farsightedness". This term is used to describe the opposite of nearsightedness. The focus of the light is not quick enough due to lack of natural focusing power in the eye, leaving an unfocused image on the retina. There is another condition called presbyopia that is often confused with farsightedness.

Presbyopia occurs when the lens in the eye becomes "stiff" and the muscle can no longer control it to focus the light properly between far and near objects. By about age 40 to 45, this focusing ability is significantly diminished and the eyes can no longer focus on close objects. This condition is directly related to aging and is not a refractive problem that can be corrected with LASIK.

Astigmatism The last condition is called Astigmatism.

This is different than the two conditions described above. This occurs when the surface of the cornea is not round in shape like a basketball. There is an uneven shape to the surface more like that of a football. The resulting view is distorted since there is not one sharp focal point in the eye.

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