Human eye shapes can affect vision. There are several different types of eyeball shapes: a normal eye, or one that’s emmetropic; an elongated or myopic eyeball, which causes nearsightedness; and a shortened or hyperopic eyeball, which results in farsightedness. The cornea and lens of the eye can also be shaped differently and affect vision.
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Emmetropia refers to an eye with a cornea and lens that focuses light precisely on the retina. The normal human eyeball measures about 24-25 millimeters in diameter, or approximately 1 inch, according to T. Montgomery, optometric physician. The eye is slightly flattened at the front and back in a roughly spherical shape.
About 30 percent of people are myopic, which means that their eyeball is longer than normal -- or that their cornea is curved more than normal -- reports the American Optometric Association (AOA). When the light rays fall in front of the eye, the retina makes it easy to see near objects, but difficult to see objects far away. According to the U.S. National Library of Medicine, myopia often begins in the school-age years, with the condition worsening until the early twenties, when the condition stabilizes.
Hyeropia occurs in people whose eyeballs are shorter than normal, or that have too little curvature to the cornea. Light rays are focused behind the retina, which makes it easy to see faraway objects, but hard to see nearby objects, according to CNN Health.
In astigmatism, the shape and length of the eyeball are normal, but the curvature of the cornea or the lens is abnormal. These structures are normally spherical, but with people who have an astigmatism, the cornea or lens are either football or cylinder shaped. According to the CNN Health website, the curvature produces blurriness which is usually more pronounced in a diagonal, horizontal or vertical direction.