What are myopia, hyperopia and astigmatism?
Patients with myopia, or nearsightedness, have steep curvature in one or both corneas; they can focus on nearby objects, but distant objects appear blurry. For hyperopic or farsighted patients, shallow corneal curvature causes nearby objects to appear blurry while objects in the distance are clear. Astigmatism causes objects that are close or at a distance to appear blurry or doubled. Most people have some degree of astigmatism, which often occurs in combination with myopia or hyperopia.
The optical system of the eye works like a camera lens to focus light rays on the retina in the back of the eye. Two-thirds of the optical power of the eye is determined by the surface contour of the cornea while the human lens inside the eye determines one-third of the optical power of the eye. In the case of nearsightedness (myopia), the optical system of the eye is too powerful and focuses light rays in front of the plane of the retina. Nearsightedness would be like taking a picture with a camera of something far away with the lens focused for something up close. With nearsightedness either the surface contour of the cornea is too steep or the length of the eye is too long. To reverse myopia, the excimer laser flattens the corneal contour. ^top In the case of farsightedness (hyperopia), the optical system of the eye is not powerful enough and focuses light rays on a plane behind the retina. Farsightedness is like taking a picture with a camera of something up close with the camera f
Related Questions
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