Generality/Definition
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Astigmatism usually occurs when the front surface of the eye, the cornea, has an irregular curvature. Astigmatism is one of a group of eye conditions known as refractive errors. Refractive errors cause a disturbance in the way that light rays are focused within the eye. Astigmatism often occurs with nearsightedness and farsightedness, conditions also resulting from refractive errors. Astigmatism is not a disease nor does it mean that you have bad eyes. It simply means that you have a variation or disturbance in the shape of your cornea. Astigmatism is very common. Some experts believe that almost everyone has a degree of astigmatism, often from birth, which may remain the same throughout life. The exact reason for differences in corneal shape remains unknown, but the tendency to develop astigmatism is inherited. For that reason, some people are more prone to develop astigmatism than others.
Source: Astigmatism (kellogg.umich.edu)
Symptoms
Treatment
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If the degree of astigmatism is slight and no other problems of refraction, such as nearsightedness or farsightedness, are present, corrective lenses may not be needed. If the degree of astigmatism is great enough to cause eyestrain, headache, or distortion of vision, prescription lenses will be needed for clear and comfortable vision. The corrective lenses needed when astigmatism is present are called Toric lenses and have an additional power element called a cylinder. They have greater light-bending power in one axis than in others. Your eyecare professional will perform precise tests during your eye examination to determine the ideal lens prescription. Refractive surgery may be able to correct some forms of astigmatism.
Source: Astigmatism (kellogg.umich.edu)
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Clinicians and surgeons have searched constantly for the most successful device or procedure to treat this refractive error. Nonsurgical devices include spectacles and contact lenses. To date, these devices are being improved continuously to address the complex problem of astigmatism. Initial surgical approaches include astigmatic keratotomy, compression sutures, and wedge resection. Recent surgical procedures involve the use of the excimer laser in PARK and LASIK with or without wavefront-guided technology. PRK is the application of ultraviolet high-energy photons (193-nm wavelength) of the ultraviolet range generated by an argon fluoride excimer laser to the anterior corneal stroma to change its curvature and, thus, to correct a refractive error. The physical process of remodeling by PRK is called photoablation. This surgical procedure reshapes the central cornea to a flatter shape for people who are nearsighted and a more curved surface for people who are farsighted.
Source: Astigmatism, PRK (emedicine.com)
Statistics
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The incidence of clinically significant astigmatism has been reported to be 7.5-75%, a wide range that primarily depends on the specific study and an author's definitions. Studies have estimated that approximately 44% of the population has more than 0.50 D of astigmatism, 10% of the population has more than 1.00 D, and 8% of the population has 1.50 D or more
Source: Astigmatism, PRK (emedicine.com)
Illustrations
Scientific articles:
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