A refractive error is an error in the focusing of light by the eye and commonly causes blurred or distorted vision. There are several types of refractive errors, which are explained below.
What is nearsightedness?
Nearsightedness (myopia) is when the eye is too long or the curvature of the cornea is too steep and the focus of the rays of light that enter the eye fall short of the retina. The result, is a blurry view of distant objects.
What is astigmatism?
Astigmatism can exist alone or in combination with nearsightedness or farsightedness. With this condition the cornea becomes oval-shaped like a football instead of round like a basketball. An irregular shaped cornea or lens prevents light from focusing at a single point on the retina, which is located at the back of the eye. As a result, vision becomes blurred or doubled at any distance.
What is farsightedness?
Farsightedness (hyperopia) occurs when an eye is too short or the curvature of the cornea is flat. Light rays entering the eye focus behind the retina, and as a result a blurred image is produced, especially with near objects.
What is presbyopia?
Presbyopia is when the lens of the eye loses the ability to change focus. This occurs as part of the natural aging process and usually begins around 40 to 45 years of age. When we lose this ability to change focus it prevents us from seeing both near and distance simultaneously. A person will need to have extra magnification in his or her glasses in the bottom or bifocal part. A nearsighted person over 40 or 45 years of age will be able to see up close if they remove their glasses since their eyes naturally focus at near, but if they wear distance glasses they will then need a bifocal if they want to see near. Since this is part of the natural aging process, a person will develop the lens changes whether they have refractive surgery or not.