Bachiller

What are the different types of refractive errors?
Myopia (nearsightedness)
A myopic eye is longer than normal, so that the light rays focus in front of the retina. Close objects look clear but distant objects appear blurred. In myopia, distant objects are blurry because the eye is too long, and images focus in front of the retina instead of on it. Myopia is inherited and is often discovered inchildren when they are eight to twelve years old. During the teenage years, when the body grows rapidly, myopia gets worse. Between the ages of 20 and 40, there is usually little change.
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If the myopia is mild, it is called low myopia. Severe myopia is known as high myopia. If you have high myopia, you have a higher risk of detached retina. It is important to have regular eye examinationsby an ophthalmologist (medical eye doctor) to watch for any changes in the retina. If the retina does detach, a surgical operation is the only way to repair it.
Hyperopia (farsightedness)
A hyperopic eye is shorter than normal. Light from close objects, such as the page of a book, cannot focus clearly on the retina. In hyperopia, the eye is too short for images to focus on the retina, so closeobjects are blurry.
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Like nearsightedness, farsightedness is usually inherited. Babies and young children tend to be slightly hyperopic. As the eye grows and becomes longer, hyperopia lessens.
Astigmatism (distorted vision)
The cornea is the clear front window of the eye. A normal cornea is round and smooth, like a basketball. When you have astigmatism, the cornea curves more in onedirection than in the other, like a football. Astigmatism distorts or blurs vision for both near and far objects. It's almost like looking into a funhouse mirror in which you appear too tall, too wide or too thin. You can have astigmatism in combination with myopia or hyperopia.
Presbyopia (aging eyes)
When you are young, the lens in your eye is soft and flexible. The lens of the eye changes its shapeeasily, allowing you to focus on objects both close and far away. After the age of 40, the lens becomes more rigid. Because the lens can't change shape as easily as it once did, it is more difficult to read at close range. This perfectly normal condition is called presbyopia. You can also have presbyopia in combination with myopia, hyperopia or astigmatism.
How are refractive errors corrected?Eyeglasses
Glasses are an easy method to correct refractive errors. They can also help protect your eyes from harmful light rays, such as ultraviolet (UV) light rays. A special coating that screens out UV light is available when you order your glasses. Bifocals are glasses that are used to correct presbyopia. They have a correction for reading on the bottom half of the lens and another for seeingdistance on the top. Trifocals are lenses with three different lens corrections in one set of eyeglasses. If you don't need correction for seeing distance, you can buy over-the-counter reading glasses to correct presbyopia. No exercise or medication can reverse presbyopia. You will probably need to change your prescription from time to time between the ages of 40 and 60, because your lens willcontinue to lose flexibility.
Contact lenses
There are now a wide variety of contact lenses available. The type that is best for you depends on your refractive error and your lifestyle. If you want to wear contact lenses, discuss the various options with your ophthalmologist. You may have heard of a process called orthokeratology to treat myopia. It uses a series of hard contact lenses togradually flatten the cornea and reduce the refractive error. Improvement of sight from orthokeratology is temporary. After the use of the lenses is discontinued, the cornea returns to its original shape and myopia returns.
Refractive surgery
Radial keratotomy is a surgical operation to improve myopia by changing the curve of the cornea over the pupil. The surgeon makes several deep incisions...