Refractive Errors

Myopia, Hyperopia, Astigmatism and Presbyopia

The cornea is the transparent tissue that covers the front of the eye. (Read about “The Eye”) It provides a physical barrier that protects the eye. It is also the part of the eye that helps focus light to create an image on the retina. The retina is the paper-thin tissue at the back of the eye that starts the translation of light into vision. If the shape of the cornea isn’t right, the image on the retina will be distorted. Since refraction is the bending and focusing of light, imperfections in the focusing power of the eye are called refractive errors.

The Food and Drug Administration (FDA) and the American Academy of Ophthalmology (AAO) say there are four primary types of refractive errors:

Myopia – In myopia or nearsightedness, people have more difficulty seeing distant objects as clearly as near objects. AAO says that in myopia, the problem is that the eye is too long and images focus in front of the retina instead of on the retina. AAO says myopia is usually inherited and is often discovered in children under age 12, often during routine eye exams. (Read about “Eye Exams”) Between the ages of 20 and 40, there is usually little change.

Hyperopia – Persons with hyperopia or farsightedness, have more difficulty seeing near objects as clearly as distant objects. A hyperopic eye is too short for images to focus on the retina, so close-up objects are blurry.

Astigmatism – Astigmatism is a distortion of the image on the retina caused by irregularities in the cornea or lens of the eye. Combinations of myopia and astigmatism or hyperopia and astigmatism are common, according to FDA.

Presbyopia – This is the one most people notice as they get older. When we’re young, the lens of the eye is soft and flexible. But as we age, it becomes more rigid. This makes it more difficult to read at close range. AAO says you can have presbyopia in combination with myopia, hyperopia or astigmatism.

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