What is astigmatism?
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Figure 3: Comparison between shapes of normal and astigmatic corneas
Astigmatism is a condition of the eye that results in blurred or distorted vision caused by an incorrectly shaped cornea [see Figure 3], which is the "tissue that forms a transparent, curved structure in the front of the eye [that] refracts light before it enters the eye (Edwards et al. 506)", or by an incorrectly shaped lens. An irregularly shaped cornea or lens prevents light rays from properly focusing on the retina, which is a layer of light sensitive cells called rods and cones at the back of the eye. As a result of the light rays not being able to focus on the retina, vision becomes blurred or distorted.
Astigmatism is a very vision problem. According to recent statistics, approximately every 1 in 6 Americans suffer from astigmatism (rightdiagnosis). Most people are born with some degree of astigmatism. In fact, it is very rare for a person be born with a perfectly round, "golf ball shaped" cornea.
Astigmatism belongs of a group of vision disorders called refractive errors, which are problems with the eye that do not allow light rays to properly refract or focus properly. This leads to the rays not being able to reach the retina, which in turn leads to a blurred image . Astigmatism often occurs in conjunction with other refractive errors, such as myopia (near-sightedness), hyperopia (far-sightedness), and presbyopia, a condition in which the muscles of the eyes can no longer control the lens; usually caused by ageing (Medical News Today).
Astigmatism is a very vision problem. According to recent statistics, approximately every 1 in 6 Americans suffer from astigmatism (rightdiagnosis). Most people are born with some degree of astigmatism. In fact, it is very rare for a person be born with a perfectly round, "golf ball shaped" cornea.
Astigmatism belongs of a group of vision disorders called refractive errors, which are problems with the eye that do not allow light rays to properly refract or focus properly. This leads to the rays not being able to reach the retina, which in turn leads to a blurred image . Astigmatism often occurs in conjunction with other refractive errors, such as myopia (near-sightedness), hyperopia (far-sightedness), and presbyopia, a condition in which the muscles of the eyes can no longer control the lens; usually caused by ageing (Medical News Today).
Types of Astigmatism
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Figure 5: Diagram of the eye
There are multiple types of astigmatism, but the types of astigmatism that occur most frequently in the general population are corneal and lenticular astigmatism.
Corneal astigmatism, which is the most common type of astigmatism, occurs when the cornea is not perfectly spherical in shape. People with this kind of astigmatism usually have oval- or football-shaped corneas. Light rays are forced to refract in an abnormal fashion and this causes the light to focus on the retina in multiple different points, instead of one, causing blurred images (Medical News Today).
Lenticular astigmatism is almost the same as corneal astigmatism, but has a few differences. The main difference with lenticular astigmatism is that it is the lens of the eye, instead of the cornea, that is improperly shaped. The lens, along with the cornea, work to focus light in one spot on the retina, and when then lens is not shaped properly, blurred or distorted vision occurs. People with diabetes often develop lenticular astigmatism as a continuous high blood sugar causes the shape of the lens to change over time. This, however, is a very slow process; it can take many years for the astigmatism to progress to a point where treatment is needed (Medical News Today).
Corneal astigmatism, which is the most common type of astigmatism, occurs when the cornea is not perfectly spherical in shape. People with this kind of astigmatism usually have oval- or football-shaped corneas. Light rays are forced to refract in an abnormal fashion and this causes the light to focus on the retina in multiple different points, instead of one, causing blurred images (Medical News Today).
Lenticular astigmatism is almost the same as corneal astigmatism, but has a few differences. The main difference with lenticular astigmatism is that it is the lens of the eye, instead of the cornea, that is improperly shaped. The lens, along with the cornea, work to focus light in one spot on the retina, and when then lens is not shaped properly, blurred or distorted vision occurs. People with diabetes often develop lenticular astigmatism as a continuous high blood sugar causes the shape of the lens to change over time. This, however, is a very slow process; it can take many years for the astigmatism to progress to a point where treatment is needed (Medical News Today).
Citations:
Edwards, Lois, Nancy Flood, Eric Grace, Craig Jackson, Michael Mazza, Jim Ross, Jenna Dunlop, Katherine Hamilton, Jennifer Parington, and Trudy L. Rising. "12.3 Lens Technologies and the Human Eye." On Science 10. By Tom Dickinson. Toronto, ON: McGraw-Hill Ryerson, 2009. 502-11. Print.
Nordqvist, Christian. "What Is Astigmatism? What Causes Astigmatism?" Medical News Today. MediLexicon International, 26 July 2009. Web. <http://www.medicalnewstoday.com/articles/158810.php>..
Image Credits:
Diagram of the Eye. Digital image. N.p., n.d. Web. <http://www.nei.nih.gov/health/eyediagram/images/NEA08.gif>.
Difference Between Astigmatic and Not Astigmatic Sight. Digital image. Ull Man Eye. N.p., n.d. Web. <http://www.ullmaneye.com/Astigmatism.jpg>.
Images of Astigmatic Eye. Digital image. Accuvision.co.uk. N.p., n.d. Web. <http://www.accuvision.co.uk/astigmatism.html>.
Edwards, Lois, Nancy Flood, Eric Grace, Craig Jackson, Michael Mazza, Jim Ross, Jenna Dunlop, Katherine Hamilton, Jennifer Parington, and Trudy L. Rising. "12.3 Lens Technologies and the Human Eye." On Science 10. By Tom Dickinson. Toronto, ON: McGraw-Hill Ryerson, 2009. 502-11. Print.
Nordqvist, Christian. "What Is Astigmatism? What Causes Astigmatism?" Medical News Today. MediLexicon International, 26 July 2009. Web. <http://www.medicalnewstoday.com/articles/158810.php>..
Image Credits:
Diagram of the Eye. Digital image. N.p., n.d. Web. <http://www.nei.nih.gov/health/eyediagram/images/NEA08.gif>.
Difference Between Astigmatic and Not Astigmatic Sight. Digital image. Ull Man Eye. N.p., n.d. Web. <http://www.ullmaneye.com/Astigmatism.jpg>.
Images of Astigmatic Eye. Digital image. Accuvision.co.uk. N.p., n.d. Web. <http://www.accuvision.co.uk/astigmatism.html>.