Contact Lenses ABC
To overcome this obstacle, a range of new rigid materials were developed between the 1970s and 1990s that allowed for oxygen to pass through to the eye. These contact lenses came to be known as Rigid Gas Permeable (RGP). All of the lenses created to this time were considered hard, but the RGP lenses offered more comfort to the wearer and better health for the eye. For contact lens wearers who have astigmatism or distorted corneal shapes, RGP have some unique qualities that are of a great benefit. RGP lenses can provide the distorted cornea shape with a new refracting surface, thus greatly improving vision. This is done in part by trapping the eyes own tears underneath the surface of the lens. Tears have a refractive index very similar to that of the cornea, thus the contact lens creates a sort of new cornea through which the wearer experiences better vision. Hard contact lenses last for a couple of years before they need to be replaced. As long as they are properly maintained, they should last at least 2 years. These types of lenses do require a few days for the eye to completely adjust to the feel of the material. The wearer usually has them in for about two hours the first day, four the next, and gradually moves towards being able to wear them all day. Once the eye adjusts, wearing these types of contact lenses is easy and comfortable. Some contact lens wearers prefer the hard lenses to the soft because they easily go on the eye and do not require placing ones fingers on the eye to remove them. Soft contact lenses are a fairly recent development in the field of eye care. Hydrogel lenses were invented by Otto Wichterle and were first used in some countries in the 1960s, but did not receive the Food and Drug Administrations approval until 1971 under the name of Soflens. Soft contact lenses are of almost immediate comfort to the wearer, thus they became more popular and were prescribed more often than hard lenses. The materials used in soft lenses were modified many times over the next 25 years to increase the amount of oxygen allowed through to the eye. Wearers of soft contact lenses need to take extra care with the lenses. They are easily torn and the maintenance of them is more involved than with hard lenses, which is one of the reasons why disposable contact lenses have become available. The wearer throws the pair of lenses away at the end of the day and starts with a fresh pair in the morning. This is convenient as the wearer does not have to worry too much about tearing the lens, but if that does happen, a new pair of lenses can be opened. Silicone hydrogels were the next major breakthrough in contact lens technology. These lenses, introduced in 1999, were originally designed for extended wear. Silicone has a material with high oxygen permeability and these lenses combined the benefits of silicone with the comfort of the hydrogel. Recently, the silicone hydrogels are being used for daily wear lenses as well as the extended wear. For some clinical purposes, a variety of hybrid contact lenses are being used. These lenses are often referred to as piggybacking and entail the use of a hard contact lens over a soft lens. This is done for several reasons; among them are increased optical strength and optimal comfort. The Differences between Vision and Eyesight | ||
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