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The optical system of the eye consists of the cornea, vitreous body, and the lens. The optical system bends rays of light to focus exactly on the retina of the eye. This bending of light rays is called refraction. Refractive errors in the eyes happen when the lens and the cornea don’t focus properly the light rays on the retina. Good vision is the result of sharp images being focused on the retina. The retina is the sensory nerve layer of the eye.

If the point of refraction is in front or behind it, not on the retina, blurry images are produced. This is called refractive error. The result is eye conditions such as near-sightedness, known as myopia, far-sightedness, known as hyperopia, astigmatism and presbyopia.

Normal vision is emmetropia. With emmetropia, the focusing powers of the cornea and the lens are perfectly matched to the length of the eye ball.

In myopia, the cornea is too curved for the eye ball. Distant objects cannot be seen clearly because light rays are focused in front of the retina. A person with myopia is able to see close objects clearly, but those objects at a distance appear blurry. Myopia is the most common type of refractive error in Asia.

In hyperopia, people are able to see far away objects relatively sharply but not so with the closer targets. The cornea is too flat or the lens, and too weak for the length of the eye ball. As a result, the lens and the cornea focus the light rays behind the retina.

In astigmatism, images of objects at both close and far distances appear distorted. The reason for this usually is the shape of the cornea. It resembles more the shape of an egg than a ball. The result is that light rays are bent in different directions and do not focus on one refractive point on the retina.

For additional information on Lasik Eye Surgery, go to Lasik Consumer Guide.