Although contact lenses have been around for more than 100 years, modern contacts made of plastic rather than glass, were introduced in 1948. They are worn directly on the cornea of the eye and, if properly fitted, can provide nearly natural vision.
The first plastic lenses were made of hard plastic called PMMA (polymethyl methacrylate) and did not deliver oxygen to the cornea. In 1971, soft contacts were introduced. Soft lenses are made from a water-loving or hydrophilic polymer that can bind up to 74 percent water. Soft contacts quickly replaced hard lenses in popularity, as they are generally more comfortable for the wearer.
The silicone hydrogel lens entered the market in 1999, and have become the fastest growing contact lens segment worldwide. The material is resistant to dehydration and allows for a high oxygen transmission to the eye. Contact lenses are a medical device, and as such, they must be prescribed and properly fitted by an eye care practitioner. They are grouped based on the material they are made of, length of wear, frequency of disposal, and lens design.
Until the introduction of extended wear contact lenses in 1979, all contacts needed to be removed and cleaned nightly. Today, eye care professionals can prescribe an extended wear lens, which can be worn overnight for up to seven days without removal; a continuous wear lens, which can be worn for as long as 30 days without removal; and a daily wear lens, which must be removed every night.
The major disadvantage of contact lenses is that proteins and lipids, which are naturally found in tears, adhere to its surface, making it prone to natural deposits, such as calcium. Eye discomfort and dryness can result from the deposits creating a water-rejecting film on the front surface of the lens. The deposits can also provide a source of nourishment for infection-causing bacteria. This makes it especially important to follow the advice of one’s eye care practitioner regarding lens care and replacement. The primary function of a contact lens is to address the vision problem it has been prescribed to correct. Eye care professionals must work to find a lens that properly fits the eye of the patient, while considering other eye conditions the patient may have, such as dry eye.
Contact lenses come in several designs – spherical, astigmatic (toric), bifocal, multifocal, keratoconus and orthokeratology. Spherical lenses have a rounded shape and correct myopia (near-sightedness) or hyperopia (far-sightedness). Astigmatic or toric lenses mainly correct for astigmatism, but also for myopia and hyperopia, as astigmatism can occur in both conditions. Bifocal lenses contain two different zones for near and far vision. Multifocal lenses contain several different zones providing for near, intermediate and distance vision, a combination that results in clear vision throughout. Keratoconus lenses are specially designed to correct irregularly shaped corneas, which cause distorted vision. Only these lenses can accommodate the irregularity and provide a clear and comfortable solution. Orthokeratology lenses are designed to reshape the cornea while the wearer sleeps, allowing them to be lens free during the day. In the United States, one out of five people who need vision correction wear contact lenses. Because contact lenses are worn directly on the cornea, wearers typically find them to be more beneficial than eyeglasses.
5 reasons to wear contact lenses:
2) The contact lens wearer may notice that the quality of vision appears more natural. This benefit is especially important in sports and while driving, when peripheral vision and accurate depth of field is necessary.
3) Contact lenses provide vision that is free of annoying obstructions and reflections.
4) Contact lenses don’t fog up with varying ambient temperatures, nor do they require constant adjustment, as is common with eyeglasses.
5) Although the majority of contact lenses are worn for vision correction, there are lenses that are manufactured and distributed as cosmetic and therapeutic lenses. The cosmetic application is probably the most common. Wearers can select a color enhancing or an opaque color contact lens to match their mood or wardrobe. Although color contact lenses can be made available to someone who does not need corrective vision, a valid prescription is required to obtain any kind of contact lens.