The lenses that are produced as an alternative to glasses and attached to the front surface of the cornea to correct the refractive errors of the eye are called contact lenses. Contact lenses can be used for correcting refractive errors, but also for cosmetic and therapeutic purposes. The principles of refraction and optics apply to contact lenses, similar to eyeglasses. These are the correction of the existing defect by replacing the corneal curvature, which occurs according to the degree of myopia and hyperopia, with a contact lens surface. Since astigmatisms are mostly caused by the distortion of the front surface of the cornea, either hard contact lenses or soft lenses (toric lenses) specially produced for astigmatism should be used. While the numbers of glasses and contact lenses are the same in small numbers, as the number increases, myopes are smaller than glasses and hypermetropes are more they should use a lens with a large number.

Gas Permeable Rigid Lenses They get this name because they allow oxygen to pass into the eye, and due to these features, they disrupt the corneal epithelial metabolism less than the obsolete hard lenses. Since they do not take the shape of the cornea, they are especially preferred in cases such as high astigmatism and keratoconus. Soft Lenses There are many different types: Daily used 1-day-lasting lenses, daily-used 1-month-lasting lenses, daily-used 3-month-lasting lenses, daily-used 1-year-lasting lenses, 1-month-wearing 1-month-lasting lenses, therapeutic lenses used for the treatment of some eye diseases, bifocal lenses, and colored like lenses. They are very comfortable to use. Most of the lenses used to correct the defect in the eye are colorless and do not change the appearance when placed on the eye. As long as they are attached, they remove the defect and provide a clear image.