Visual Problems

There are four main types of vision disorders:

Myopia:

Near-sightedness or blurry vision for objects at a distance.Contact Lenses for Myopia: Regular lenses (spherical).  Myopic people can see close objects clearly, but distant objects are out of focus.  The main cause is an eyeball which is longer than normal from front to back.  The extra length means light from distant objects is focused short of the retina.  Light continues on to reach the retina, but the projected image is blurred. Myopia also can occur when the curvature of the cornea is “over bulged”.  The resulting extra refraction has the same result as the elongated eyeball: focus falls short of the retina. Some people have both errors.

Hyperopia:

Far-sightedness or blurry vision for close objects.
Contact Lenses for Hyperopia: Regular lenses (spherical). Hyperopia occurs when the eyeball is too small, or short.  The reduced length means that the point of focus lies beyond the back wall of the eye, and light rays are not yet in focus when they arrive at the retina. The result is a blurred image. Improper corneal curvature can also cause hyperopia.  If the cornea is too flat, not enough refraction of light rays from near objects takes place to bring them into focus on the retina. Normally, all young children have a small degree of hyperopia that decreases as they progress through their teens. Despite their hyperopia, most youngsters can see well at all distances since the crystalline lens is sufficiently flexible to counteract minor refractive errors.

Astigmatism:

Uneven cornea, which produces ghosting or double images.
Contact Lenses for Astigmatism: Toric Lenses. Astigmatism is an overall inability of the eye to focus clearly at any distance because of uneven curvatures of the  cornea. Essentially, the cornea is oval, having a surface shaped more like a football or the back of a spoon rather than spherical.  Frequently associated with myopia, astigmatism can cause light rays to focus at more than one point on the retina and objects at all distances appear distorted—in much the same way as fun house mirrors.Virtually all corneas have at least a tiny degree of astigmatism.  For many, the resulting distortion is not discernible, but as the curvature of the cornea becomes more uneven, image distortion increases. Eyeglasses, hard contact lenses or toric soft contact lenses are used to correct astigmatism, which is often inherited.

Presbyopia:

Aging eye, or deterioration of near vision.
Contact Lenses for Presbyopia: Bifocal Lenses. As we get older, the crystalline lens in each of our eyes loses its suppleness and becomes less flexible. When this occurs, our ability to focus close-up diminishes and our eyes are said to be presbyopic. 
This condition usually becomes noticeable between the ages of 40 and 50, and those with otherwise normal eyesight find it increasingly difficult to read or do close-up activities without bifocal contacts or reading glasses. Many prefer multi-focal lenses to see clearly at all distances.