Contact vision correction

Contact vision correction has a centuries-old history. Leonardo da Vinci and Rene Descartes were interested in this issue. A. Fick and E. Kalt were the first to report on the use of contact lenses in 1888. The beginning of the revolution in contact vision correction can be considered the end of the 50s, when Czech scientists O. Wichterle and D. Lim synthesized a hydrophilic material for the manufacture of soft lenses, and in 1966 their mass production began. In our country, the first specialized laboratory was organized at the Helmholtz Moscow Research Institute of Gynecology and Microbiology in 1956.

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

Between the back surface of the lens and the front surface of the cornea there 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 tear film and the cornea. The tear fluid fills all the 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 of the cornea shape, and then pass almost in a homogeneous optical medium. Contact lenses correct astigmatism well, compensate for optical aberrations, change the position of the cardinal points in the optical system little and have an insignificant effect on the image size, do not limit the field of view, provide a good overview, are not visible to others.

Contact lenses are classified depending on the material they are made of. According to this criterion, two classes of lenses are distinguished: hard (RCL) and soft (SCL). The properties of the material from which contact lenses are made largely determine their tolerability by patients.

Rigid contact lenses can be gas-impermeable or gas-permeable. Gas-impermeable hard contact lenses are already becoming a thing of the past: they are made of oxygen-impermeable polymethyl methacrylate, require long-term adaptation to these hard contact lenses, and their use time is limited. Gas-permeable hard contact lenses are tolerated much better by patients.

According to their purpose, soft contact lenses are divided into optical (the majority of them), therapeutic and cosmetic.

According to the wearing regimen, soft contact lenses are divided into daily wear (they are worn during the day and removed at night), flexible wear (the patient can sometimes wear the lenses for 1-2 nights), extended wear (such soft contact lenses can be worn without removing for several days) and continuous wear (up to 30 days in a row).

The ionicity of the material and its moisture content (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 deposit accumulation. Lenses with a low moisture content are stronger and more durable, but less physiological.

According to the frequency of replacement, soft contact lenses are divided into lenses of one-day replacement (put on in the morning and throw away in the evening), lenses of frequent planned replacement (within 1 month and more often), planned-replaceable lenses (replacement after 1-6 months) and traditional lenses (replacement after 6-12 months). Lenses of one-day replacement are the "healthiest", but also the most expensive option.

According to their optical properties, contact lenses can be spherical (most lenses are like this, and they come in versions with any replacement period and wearing mode), toric (for correcting astigmatism), and multifocal (for correcting presbyopia).

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