Myopia is a vision problem experienced by about one-third of the population. People with myopia have difficulty in seeing objects at a distance.
Myopia occurs when the eyeball is too long, or the eye's focusing mechanism is too powerful (cornea and lens)In this case light rays are focused in front of the retina. Lenses to correct this common disease are thinner in the center than on the edges to help redirect light rays to the retina, and are "minus" lenses called concave lenses as well.
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Hyperopia is a common vision problem and if you suffer from Hyperopia you can see distant objects very well, but have difficulty seeing objects that are close.
Hyperopia occurs when the eyeball is too short from front to back, or the eye's focusing mechanism is too weak. This way light rays are focused behind the retina, not on it. An estimated 60% of the population is farsighted to some degree. This vision problem is corrected with, a "plus" lens (convex). This lens is thicker in the center and thinner on the edges.
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Astigmatism is the most common vision problem and often accompanies nearsightedness or farsightedness.
Astigmatism is characterized by an irregularly shaped cornea; the cornea is shaped more like an oblong football than a spherical baseball that is the normal shape. In this case light images are focused on two separate points in the eye, creating this way a distorted image. Contact lenses designed to correct astigmatism are fitted for each individual. The cornea is measured and special toric lenses are used to direct light rays to one single spot on the retina. Rigid Gas Permeable (RGP) lenses, due to their firm design, offer a high degree of correction for this eye problem and sometimes it does not require a complicated toric design, as they can compensate for the irregularly shaped cornea.
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Presbyopia is also known as "aging eye”. This is an eye problem that occurs as the eye’s lens grows older and begins to lose elasticity needed to switch focus between near and far objects.
Presbyopia affects most people around the age of forty but it can occur in the case of teenagers as well. Bifocal lenses are used to correct presbyopia. Bifocal means two points of focus- the main part of the lens contains a prescription for nearsightedness/farsightedness, while the lower part of the lens has the stronger near prescription for close work. |
Eye Diseases
Eyes do not actually see objects -they see the light that objects reflect. When these light rays enter the eye, they converted into electrical signals by the retinal nerves. These signals are then sent to the brain and the brain interprets them as visual images. In a normal eye light rays enter the eye through the "cornea" and are focused behind the pupil at a point directly on the retina. As only about four in ten people have normal sight, the light rays must be refocused with the use of corrective lenses.
