Refractive Eye Errors 

How does the eye work?

The eye is like a camera that has two lenses. One of these lenses is the crystalline lens inside the eye. The other lens is the cornea, which is positioned in the eye like a watch crystal but actually provides 2/3 of the eye’s focusing power. When the light rays entering the eye are perfectly focused on the retina, the eye is neither nearsighted nor farsighted. This condition is called emmetropia.

What is refractive surgery?

Refractive surgery involves the use of lasers or other devices to treat the refractive errors of the eye. Radial keratotomy has been practiced in the United States for nearly 20 years, but it has now been surpassed by the use of the excimer laser for treating near-sightedness, far- sightedness and astigmatism.

The FDA approved laser that we use to treat near-sightedness (myopia), far-sightedness (hyperopia) and astigmatism is the VISX Star excimer laser. The VISX laser has received FDA approval for treatment of near-sightedness (myopia) up to -14.00 (with astigmatism up to 5 diopters), far-sightedness up to +6.00 diopters (with astigmatism up to 1 diopter). This laser is located in the Laser Eye Center of Iowa at 818-5th Avenue. Dr. Husain is certified to use the VISX laser.

Excimer: Ablation on Human Hair

What are refractive errors of the eye?

Myopia, or near-sightedness, occurs when the eye has too much focusing power. As a result, objects at distance are blurry, whereas objects that are close can be clearly seen (unless astigmatism is present). Typically, the myopic eye is slightly longer or has a steeper cornea compared to the normal eye.

Hyperopia, or far-sightedness, occurs when the eye lacks sufficient focusing power. This usually causes objects at a distance to appear blurry, and near objects are seen even less clearly. Typically, the far-sighted eye is slightly shorter or has a flatter cornea than the normal eye.

Astigmatism, is a condition in which light rays in different orientations are brought to different points of focus. A useful analogy is the comparison of a basketball to a football. The surface of a basketball has equal curvature in all directions, whereas a football is flatter in one orientation and steeper in the other. The surface of the football represents the situation that is present when the eye has astigmatism. Usually, the astigmatism occurs in the cornea. This can often be corrected with glasses or contact lenses, or in many instances, treated with refractive surgery

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Presbyopia, is a natural condition that typically becomes noticeable around age 45. In children and young adults, the crystalline lens inside the eye can focus at a distant object and then easily increase its focusing power to look at a near object. As we get older, the lens inside the eye loses this capacity to focus in and out. As this occurs, individuals find that they need to hold reading material at greater distances. Ultimately, reading glasses are needed, typically by the mid-40s.

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