Understanding Refractive Errors and How they Affect Us

For most people, the prescription that is attached to their contact lenses or glasses is a number that means absolutely nothing. Most just know they can’t see without their corrective lenses. A refractive error is an error in the focusing of light by the eye and commonly causes blurry or distorted vision. There are several types of refractive errors including nearsightedness, farsightedness, astigmatism and presbyopia.

Nearsightedness, also known as myopia, occurs when the eye is too long or the curvature of the cornea is too steep. This causes the focus of light as it enters the eye to fall short of the retina resulting in a blurry view of the distant object. People who are nearsighted will see a minus sign (-) in front of their prescription.

Farsightedness, also known as hyperopia, occurs when the eye is too short or the curvature of the eye is flat. As light rays enter the eye, they focus behind the retina resulting in a blurry view of near images. People who are farsighted have a plus sign (+) in front of their prescription.

An astigmatism can exist alone or in combination with nearsightedness or farsightedness. An astigmatic eye is oval-shaped like a football instead of round like a normal eye. The irregular shaped cornea prevents light from focusing at a single point on the retina. This results in blurred or double vision at any distance.

Presbyopia occurs when the lens of the eye loses the ability to change focus. This occurs as part of the normal aging process and usually begins around 40 to 45 years of age. When we lose the ability to change focus, it prevents us from seeing both near and far simultaneously. A person with presbyopia will find that they need to have extra magnification  in the bottom or bifocal part of his or her glasses. A person who is nearsighted and newly presbyopic will be able to see up close if they remove their glasses. This is because their eyes naturally focus at near. If they wear glasses, however, they will need a bifocal to see near.

Understanding why things are blurry at different distances is an important part of understanding how glasses and contact lenses improve eyesight. As an alternative to corrective lenses, LASIK and PRK help restore vision to those with refractive errors by changing the way that light enters the eye. The only refractive error that cannot be corrected by LASIK or PRK is presbyopia. This is because the error is not caused by the shape of the eye but the lens becoming rigid.

If you would like to learn more about how LASIK or PRK can improve your sight, call (919) 876-2427 today.