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Your Eyes
Emmetropia
Vision in the normal eye, or the Emmetropic eye, light rays focused directly on the retina result in clear vision.
Myopia
Myopia or nearsightedness, occurs when light rays have their focal point in front of the retina instead of directly on the retina. This is normally caused by the eye being either too long or the cornea too steep, resulting in blurry distance vision.
Hyperopia
Hyperopia or farsightedness, occurs when the eye is either too long or the cornea is too flat, resulting in light rays that would have to focus behind the retina. This inability to focus within the relaxed state of the eye, makes vision blurry at close, and sometimes blurry at distance as well.
Astigmatism
Astigmatism is an optical defect of the eye just as nearsightedness (myopia) and farsightedness(hyperopia), are. Astigmatism results from the cornea having a sharper curve in one direction than the remainder of the cornea. An example of this situation is the bottom of a teaspoon where the curvature from side to side is a good deal sharper than from front to back. (Of course, this example is exaggerated and the astigmatic eye appears normal.) This results in the light rays focusing on more than one point on the retina resulting in blurry or distorted vision.
