Contact vision correction

Contact correction of vision has a long history. This question was also of interest to Leonardo da Vinci and René Descartes. The application of contact lenses was first reported by A. Fick and E. Kalt in 1888. The beginning of the revolution in contact correction of sight can be considered the end of the 50's, when the Czech scientists O. Wichterle and D. Lim synthesized a hydrophilic material for making soft lenses, and in 1966 their mass production began. In our country, the first specialized laboratory was organized in the MIIGIB them. Helmholtz in 1956

Contact lenses are a means of optical vision correction. They are directly in contact with the eye and are held by the forces of capillary attraction.

Between the posterior surface of the lens and the front surface of the cornea is a layer of tear fluid. The refractive index of the material from which the lens is made is practically the same as the refractive index of the film of the tear fluid and the cornea. The lacrimal fluid fills all deformations of the anterior corneal surface, so the light rays are refracted only on the front surface of the contact lens, which neutralizes all the imperfections in the shape of the cornea, and then passes in practically a homogeneous optical environment. Contact lenses well correct astigmatism, compensate for optical aberrations, change the position of cardinal points little in the optical system and have little effect on the image size, do not limit the field of view, provide a good view, are not visible to others.

Contact lenses are classified according to the material from which they are made. By this criterion, two classes of lenses are distinguished: rigid (LCS) and soft (MKL). The properties of the material from which contact lenses are made, largely determine their tolerability by patients.

Rigid contact lenses can be gas tight or gas permeable. Gas tight rigid contact lenses are already going down in history: they are made of oxygen-tight polymethyl methacrylate, long-term adaptation to these hard contact lenses is required, their use time is limited. Gas-permeable hard contact lenses patients suffer much better.

By appointment, soft contact lenses are divided into optical (most of them), therapeutic and cosmetic.

According to the mode of wearing, soft contact lenses of day wear are distinguished (worn during the day and at night), flexible wearing (the patient can sometimes not remove lenses 1-2 nights), prolonged wearing (such soft contact lenses can be worn without removing a few days ) and continuous wearing (up to 30 consecutive days).

The ionicity of the material and the moisture content in it (more or less than 50%) determine the comfort of wearing the lens and the timing of its replacement. Obviously, lenses with a high moisture content are more comfortable, but they are less durable and more prone to accumulation of deposits. Lenses with a low moisture content are stronger and more durable, but less physiological.

On the frequency of replacement, soft contact lenses are divided into lenses of a one-day replacement (in the morning they put on - in the evening they threw away), lenses of frequent scheduled replacement (for 1 month and more often), scheduled lenses (replacement in 1-6 months) and traditional lenses 6 to 12 months). Lenses one-day replacement - the most "healthy", but at the same time the most expensive option.

According to their optical properties, contact lenses can be spherical (most of these lenses produce their variants with any term of replacement and wearing mode), toric (for correction of astigmatism) and multifocal (for correction of presbyopia).

[1], [2], [3]