The influence of environment on the ocular contact lens

Contact lenses interact with each layer of the tear film. Although recent advances in contact lens science have led to the development of improved materials, the contact lens is still a foreign body to the eye. If a contact lens were completely biocompatible, the body would treat the lens as a natural part of the eye, and the ocular environment would not react to the presence of the lens. However, since contact lenses do not have perfect biocompatibility, the ocular environment reacts to the presence of a contact lens by forming deposits.

Deposit on a contact lens is any formation in the form of a coating on the surface or in the matrix of the lens that is not washed away and is not carried away by the film of tear fluid when blinking.

Sediment formation is a very complex phenomenon. Below is its brief description. The formation of deposits will be considered in more detail in the "Contact lens cleaners" section.

The reaction of the tear film to the contact lens depends on the contact lens material. It is important to remember that contact lenses are made of different materials - from similar plastic PMMA to a soft, sponge-like material that contains a large amount of water. Just as plastic behaves differently than a sponge, different lens materials will cause different reactions in the eye environment.

Deposits are formed on soft contact lenses as a result of the interaction of the tear fluid film with both the lens matrix and its surface.

Soft contact lenses contain 30-70% water and have molecular pores or holes where water circulates freely. When the lens is placed on the surface of the eye, the components of the tear film, which have a small size, can also freely circulate through the pores of the matrix of the soft lens.

Such circulation in the lens matrix leads to an increase in the number of centers with which the tear fluid film can interact. In this regard, the interaction with the film of tear fluid occurs in the matrix of the lens and on its surface.

The first reaction of the eye environment to the presence of a contact lens is the attraction of tear fluid proteins to the surface of the lens. This attraction happens very quickly. Protein was detected on the surface of the lens after only a few seconds of wear. The rapid deposition of proteins on the surface of biological material is not a unique phenomenon, peculiar only to contact lenses. This phenomenon also occurs during the implantation of other biologically compatible materials, such as vein prostheses and an artificial heart.

It is widely believed that the attraction of tear fluid proteins to the contact lens surface is the body's attempt to mask the contact lenses, making them more biologically compatible. The formation of such an initial protein layer can be useful, as the lens becomes more comfortable to wear and compatible with the natural eye environment. The initial protein layer changes the surface properties of the lens, making them similar to the surface properties of the cornea. As a result, the lens becomes more compatible with the ocular environment.

After the initial protein layer is deposited on the soft contact lens material, other components of the tear film may be attracted to the lens. As the duration of lens wear increases, deposits on the lens change, and not all changes are positive. All large amounts of proteins are attracted both to the lens and to the protein previously deposited on the lens. Often, the composition of such protein layers includes mucin, which becomes a component of deposits on the lens.