Materials for contact lenses

Classification of materials

 

A large number of different materials for soft contact lenses difficult to know all the physicians and clinical chemical properties of each. So they developed a classification. Materials are divided into groups by indicators such as water content and ionic characteristics. Studies have shown that within the group of materials similar to each other in many ways.

 

Group I (low water content / non-ionic polymers)

 

   - Polimakon (38%) Bausch & Lomb / Hydron

   - Krofilkon (39%) CSI

   - Hefilkon Sun (45%) BL Toric / Optima Toric

   - Tefilkon (37,5%) Ciba Vision

   - Tetrafilkon (43%) Cooper Vision

   - Femfilkon (38%) WJ

 

Group II (high water content / non-ionic polymers)

 

   - Lidofilkon B (79%) CW 79

   - Syurfilkon (74%) Permaflex

   - Lidofilkon A (70%) Hydron, Sauflon, BL 70

 

 

Group III (low water content / ionic polymers)

 

   - Etafilkon (43%) Vistakon Hydromark

   - Bufilkon A (45%) Hydrocurve 45 / Softmate I

   - Femfilkon A (38%) WJ Durasoft 2

 

Group IV (high water content / ionic polymers)

 

   - Bufilkon A (55%) Hydrocurve 55 / Softmate P

   - Perfilkon (71%) Rermafleh

   - Etafilkon A (58%) BL 58

   - Femfilkon A (55%) WJ Durasoft

   - Vifilkon A (55%) Ciba Softcon EW

 

Lenses with low water content

 

Such lenses show excellent properties when used by patients with visual impairment ranging from minus one to minus five diopters. In addition, such materials (with low water content) compatible with all methods of contact lens care, including heat treatment, hydrogen peroxide treatment, chemical disinfectants. These materials absorb little protein that extends their service life. Lenses of this material have high tensile strength and is therefore more durable than the lens of a material with a high water content. They also have good stability and are compatible with most methods of storing soft contact lenses. Since materials with low water does not absorb preservatives, no problems with obestsvechyvanyem as in materials with a high content of ?? vody.Materialy with low water content can be used for all three production techniques: turning, casting a centrifuge and casting in shape .

 

 

Lenses made of materials with high water content

 

These materials have a high oxygen permeability and are therefore perfectly suited for the production of thicker and consequently stronger lenses for both short-sighted and far-sighted for. Stronger lenses are usually thicker to provide adequate durability and ease of handling. However, this is indicated in several oxygen permeability. Due to the presence in them of significant amounts of water lenses from such materials have lower tensile strength compared to materials with a lower water content. These materials also differ poor compatibility with disinfectants. Their use is contraindicated in patients who use thermal disinfectant. Among other things, thermal disinfection causes severe eye redness and discoloration lenses. In addition, contact lenses with high water content can not be subjected to enzyme purification over time. Means are associated enzyme purification matrix material of the lens, and then enter the eyes, causing irritation. This is a significant drawback considering that the contact lens material with a high water content tend to absorb protein. In combination with enzyme cleaner incompatibility of this helps to reduce the service life of such lenses. Contact lenses with high water content usually made ways lathe cutting or molding.

 

Lenses with an average water content

 

Over the past few years have developed materials with an average water content. This usually ionic or nonionic materials with a water content of 50 to 70%. This type of material is an attempt to combine the advantages of both materials with low water content and materials with a high content of ?? vody.Obychno such materials have good physiological parameters and can produce thin lenses comfortable. The disadvantage of these materials is that they have an increased absorption of protein. Moreover, they can not be subjected to thermal disinfection.

 

The physician should choose the appropriate lens material allowing for the patient's eye to avoid problems clinical nature. For example, a patient who has a chronic problem with the release of the protein should not wear lenses with ?? ion materials with high water content. In contrast, patients with very low visual acuity (over seven diopters), recommended to wear lenses ?? of materials with middle and low water content for oxygen permeability in more peripheral areas of thick lenses.