The contact lenses are worn directly on the cornea of the eyes to correct defects in vision. All the defects that are corrected by regular eyeglasses and those which cannot be corrected with glasses can now be rectified by contact lenses.
Contact Lenses
The first contact lens to be used as an eye aid was made by A.E. Fick in 1887. These early lenses were first made by blowing glasses and then by grinding and polishing the bottoms of glass test tubes. These lenses were not successful and remained just a subject of academic study for a long time. Progress was made only in 1938, when plastic (methyl methacrylate) contact lenses were developed. Form 1938 to 1950, the process adopted for making contact lenses was not simple. First the impression of the eye was taken, then a mould was prepared and then the lens was made out of it. Such lenses had a fluid under them and covered most of the eye.
After 1950, smaller lenses were used that covered only the cornea, which is the front surface of the eye, and floated on layer of tears. It was no longer nec3esar to make an impression of the eye. Optical instruments could measure the curvature of the cornea. Such lenses are usually 7 to 11 millimeters in diameter and 0.1 to 1 millimeter in thickness and can be worn all day.
To fit the contact lenses, the eyes are first tested for defects just as they would be in case of spectacle. Then the radius or curvature of the eye surface is found out by using a device called kerometer. After deciding on the diameter and power of the lens, the prescription is sent to the manufacturer for making the lens.
Contact lens are made by taking a plastic rod which is first sewn into sections and then turned on a lathe to make button shaped tablets, know as bonnets. They are given the right curvature with the help of special machines for obtaining the desired power and then finally polished. The lenses are then examined to see whether they fit the eye. Finally, they are worn on the cornea. These lenses can be worn comfortably by most people throughout the day.
Contact lenses save the bother of wearing spectacles; contact lenses provide a much wider field of vision than ordinary spectacles. They are better for active sports, since they are not easily lost or broken, and can even be used to protect against the sun. Contact lenses cannot correct all defects of the eye. They are also expensive and some people have difficulty in wearing them. In some cases people have experienced irritation after wearing them.
As research continues, smaller and more flexible lenses are being developed in order to make them less irritating to the eyes. Soft lenses of hydroxyethyle are used today in the manufacture of contact lenses.