Contact Lenses Types
Today, contact lenses are small thin plastic disks designed to correct vision by changing the way the light enters the eye by altering the curvature of the cornea. The contact lens covers both the iris (colored portion of the eye) and the pupil (the dark center of the eye). Contact lenses correct mostly Myopia (nearsightedness), Hyperopia (farsightedness), Astigmatism (irregular shape of the cornea, causing skewed vision), and Presbyopia (caused by natural aging of the eye). Contact lenses are about the size of a button and are held in place on the eye by the eyes own natural tears.
Perfect and clear vision occurs when light entering the eyes through the cornea and converge at an exact point on the retina, or the back of the eyeball. Only about 4 in 10 people have this vision. Due to eye and cornea shape, size and distances, it may be necessary for vision to be corrected through the use of lenses.
The alteration of light through the cornea is controlled by the curvature of the lens. Concave, or minus, lenses are used to treat Myopia. Convex, or plus, lenses are used to correct Hyperopia by taking the light into the before the normal cornea would, allowing the light to focus perfectly on the retina, instead of past where the retina is.
The following are the common types of contact lenses :
Spherical and Aspherical Contact Lenses
Spherical contact lenses correct the most common types of eyesight problems: Myopia and
Hyperopia. Myopia is the medical term for nearsightedness, the ability of the eye to focus on tasks and items that are closer to the eye, and the inability of the eye to focus on items that are at a distance. For patients with Myopia, items placed farther from the eye may appear blurred. Squinting may help bring these items partially into focus. Hyperopia is the medical term for farsightedness, or the ability of the eye to see clearly those items and tasks that are farther away. Items and tasks that are closer to the eye may appear blurred. Spherical contact lenses can correct these vision problems.
Spherical contact lenses have the same corrective power at each part of the lens. This allows the lens to help the eye focus and clear blurred vision. Another type of one power contact lenses are aspheric, a slightly more specialized lens. Aspheric lenses are a higher quality premium lens for patients with very slight Astigmatism and patients at the early stages of development of Presbyopia, the inability to focus on closer objects such as reading materials. Presbyopia is part of the natural aging process of the eye.
Toric Contact Lenses
Toric contact lenses are for people with Astigmatism. Astigmatism is a condition of the eye where vision is affected by an irregularly shaped cornea. People with this shape to the cornea may also have Myopia or
Hyperopia. People with Astigmatism may view images that are slightly to moderately skewed form top to bottom.
To correct the Astigmatism and the Myopia or Hyperopia, toric contact lenses need to have more than one power shaped into them at angles, as well as an anchoring mechanism to keep the contact lens from shifting around on the eye. Normally, contact lenses turn and shift on the eye with no discomfort to the wearer. Because of eye shape in patients with Astigmatism, this shifting and movement can become uncomfortable. The Toric contact lens is shaped in a way to provide a stabilizer to the lens that keeps it form shifting on the patients eye.
Patients with very mild Astigmatism, with more issues of Myopia or Hyperopia may wear aspherical or even spherical lenses with little or no problems.
Bifocal Contact Lenses
Bifocal contact lenses have different powers shaped into the lens. They differ from toric lenses because the powers are not at angles to each other.
Some lenses feature two more obvious prescriptions. The top of the lens can have a prescription for distance if needed, where the bottom section of the lens has corrections for the Presbyopia.
Other designs are progressive with different powers blended onto the lens. This eliminates the defined line between the top and bottom of the bifocal lens discussed earlier. Another option for Presbyopia patients is monovision, where one eye is fitted for a spherical lens that corrects the condition for reading, and the other eye is fitted for a spherical lens that corrects the farsightedness. The eye can then learn to differentiate between the two for specific tasks.