What are refractive errors?
Refractive errors include myopia, hyperopia, presbyopia, and astigmatism. During the refraction process, the cornea and lens bend light to focus it on the retina. When light hits the retina in the correct place, it produces good vision. In people with refractive errors, the light is not bent correctly and hits the retina in the wrong place. This results in imperfect vision.
These eye conditions are very common and most people have one or more of them. Most refractive errors can be corrected with eyeglasses or contact lenses. Surgery is also becoming a popular option to correct refractive errors.
What is myopia (nearsightedness)?
In nearsighted or myopic eyes, the cornea is curved too much, or the eye is too long, and light gets focused in front of the retina. As a result, people with myopia can clearly see close objects, but distant objects are blurry.
What is hyperopia (farsightedness)?
In farsighted eyes, the eye is too short, and the cornea is not curved enough. Images are focused on a point behind the retina. This makes close-up objects appear blurry, while faraway objects remain clear.
What is astigmatism?
Astigmatism is a condition in which the cornea is curved unevenly. A normal cornea is round, with even curves from side to side and top to bottom. With astigmatism, the cornea is shaped more like the back of a spoon, curved more in one direction than in another. This causes light to have more than one focal point and focus on two separate areas of the retina. As a result, people with astigmatism have blurry and distorted vision for both faraway and close-up objects.
Astigmatism rarely happens on its own. It is usually happens with myopia or hyperopia. Two-thirds of Americans with myopia also have astigmatism.
What is presbyopia?
Presbyopia is a condition that causes problems with focusing on objects up close. This usually happens with age. Around 40 to 50 years old, a person with presbyopia might realize he or she has trouble reading words at close distances. The letters of the phonebook might be “too small” or he or she has to hold the newspaper farther away to see it clearly. While people with presbyopia have problems with close-up vision, their ability to see far away objects stays the same.