|
In order to see clearly, objects need to be brought to a focus point precisely on the retina of the eye. The retina can be compared to the film in a camera. The light is brought to a focus point by the cornea and lens of the eye. The cornea's curvature is ideally matched to its length in the normal eye. As the normal eye ages, the lens (depicted in this schematic as the yellowish oval structure in the middle part of the eye) loses the ability to focus for reading and will require the help of reading glasses. This process is called presbyopia. Presbyopia increasingly affects your reading vision as you age and typically becomes problematic enough by age 45 to require reading or bifocal eyeglasses to correct for this problem. Presbyopia is commonly mistaken for far-sightedness (hyperopia). |
 |
|
If you are nearsighted, the cornea of your eye is overly curved or your eyeball is too long. This combination brings images of distant objects to a focus point in front of the retina. When the light reaches the retina, a blurred image is seen since the light rays spread apart after the focus point. |
 |
|
If you are farsighted, the cornea of your eye is not curved enough or your eyeball is too short. This combination of factors causes the focus point of the eye to be located behind the retina. When light reaches the retina, a blurred image is seen since the light rays have not been brought to focus on the retina. |
 |
|
If you have astigmatism, the cornea of your eye has a non-spherical shape (like a football) and does not bring light to focus at a single point. Instead, it focuses images over a range of points producing a blurred image. Both nearsighted and farsighted eyes can also have astigmatism. |
 |