Synonyms in a broader sense
Adhesive lenses, adhesive shells, adhesive lenses, glasses engl. : contact lenses
Definition
Contact lenses are thin lenses made of plastic, which rest on a tear film or directly on the cornea of the eye. Most contact lenses are visual aids which, like glasses, can be used for long-sightedness or short-sightedness. Due to the close contact with the cornea of the eye, irregularities of the cornea, such as astigmatism (astigmatism) or after injuries, can also be compensated. However, there are also colored contact lenses that are worn for purely cosmetic reasons.
History of contact lenses
As early as the 17th century, the French philosopher and scientist “René Descartes” was the first to come up with the idea of a visual aid whose lens lies directly on the eye. But it was not until the end of the 19th century that the first contact lenses were developed, which were then still made of glass and were very uncomfortable to wear due to their large diameter. It was only with the development of acrylic glass (PMMA) that it became possible to produce smaller comfortable lenses that could be worn for several hours.
Important terms about contact lenses
- Dk valueThe oxygen permeability of a contact lens is indicated with Dk/t. The higher the Dk/t, the better the oxygen supply to the cornea. There are various minimum values: For a lens that is only worn during the day, the dk/t must be at least 20 to ensure a minimum oxygen supply to the cornea.
For contact lenses that can also be worn overnight, the minimum value is 87. No corneal swelling is caused by wearing these lenses overnight. For contact lenses that claim not to alter the oxygen supply to the cornea, the Dk/t is at least 125.
- DioptresThe unit dioptres (dpt = 1/m) describes the refractive value of lenses. Lenses for the correction of myopia have negative values, for the correction of hyperopia the lenses have positive dioptres.
- BC-ValueDe BC-Value indicates the degree of curvature of contact lenses. Every cornea has an individual curvature and therefore needs suitable contact lenses to prevent damage. When fitting contact lenses, the optimal BC value is determined.
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