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Methods of manufacturing contact lenses

13 Sep 2010
Today, there are several methods for the production of contact lenses (lens purchase). The most widely used four methods:
- The method of centrifugal forces;
- Method of turning (lathe processing);
- Method "Reversible Process III»;
- The method of polymerization in the form of (casting).
Let's see what is each of them.
Method centrifugal forces (spin-cast)
This process was developed in the sixties by a group of Czechoslovak scientists led by chemist Otto Viherle (Otto Wichterle) makromolekulyarnoy Chemistry Institute in Prague, and then improved by Bausch & Lomb (contact lenses Bausch & Lomb). Like many other great achievements in science, process centrifugal forces based on a simple idea - converting rotating mass of liquid in a solid. Currently, it is used in an advanced modification and controlled by special software. The method consists in that the liquid monomer is dosed and injected directly into the rotating form that has a cylindrical wall and a concave lower surface. When rotating shapes in a special installation under the influence of centrifugal force, liquid reagents conveyed on its inner surface. The shape of the lens and its parameters are determined by indicators such as process units: temperature, speed, volume and other monomer. Due to the effects of ultraviolet radiation on liquid monomer during rotation, it is converted to polymer. Then the lens is removed from the mold, hidratiruetsya (saturated with water), subjected to sterilization and packaging. This method is the cheapest of the existing ones.
The process enables lenses with high reproducibility, stability and accuracy parameters. At the same time, the technology has limitations centrifugal forces. This technology can not get lenses with complex geometries, such torycheskye soft lenses.
In addition, lenses manufactured centrifugal molding without doctor's prescriptions are issued with base curve, according to some ophthalmologists, prevents precise selection of lenses. However, studies show that the use of lenses with a base curvature done on purpose, gives significant advantages in clinical practice. It should also be noted that because of the low thickness and high flexibility lenses manufactured centrifugal molding, handling difficult, especially if the lenses have low optical power. Move the lens in the eye is minimal. However, research results indicate that even with such minimal movements lens (only 0.1 mm) film of tear fluid is in a dynamic state. The film ensures the supply of oxygenated tears beneath the lens and helps to remove deposits from under the lens.
The method of turning (lathe cut)
This method is widely used to make soft contact lenses and some types of hard contact lenses (hard contact lens price). For turning on the machine using hard (dry) blanks with pre-polymerised material. In the production of soft contact lenses, lens processed in hard condition, then subjected to hydration. Sizes and hard lenses in various hydrated state, as calculated before processing optical and geometrical parameters of the lens in hard (dry) state, based on set parameters in the soft lens (hydrated) state.
Turning process consists of several stages:
- CNC lathe. Application of computer control allows to obtain surfaces with two or even greater number radii of curvature of the rear surface;
- Polishing to remove traces of the tool;
- Saturation with water to the desired concentration;
- Chemical removal of the lenses of impurities;
- Toning;
- Quality control and compliance parameters given value;
- sterilization;
- Packaging and labeling.
Turning method is more expensive than centrifugal Molding or casting. However, this method is very useful for making small batches of lenses, lenses with complex geometry or customized for the individual patient.
Typically, chiseled lenses are made individually for the patient Measured according to the topography of his eyes. Also widespread small-scale production. Using high-precision air bearings on machine tools allows to make Turned lenses with high repeatability of parameters. In addition, some types of design elements may only perform this method. Compared with centrifugal molding, lathe processing requires more time and labor. To perform this complex process takes about 30 minutes. As a result, the cost of lenses in four to five times higher than in the centrifugal forces.
Reversing the process III (reversive process)
This method was proposed by Bausch & Lomb. By its very nature it is combined as a connecting methods centrifugal forces and turning. It got its name because the first foreign made, and the inner surface of the lens. The outer surface is produced by centrifugal forces and internal - turning with further polishing. The result is high surface smoothness, good oxygen permeability and provides the possibility of manufacturing complex shapes lenses on specified parameters.
The front surface of the lens, obtained by centrifugal casting, has a high degree of smoothness that attaches the lens high optical performance, comfort wearing and perfect edge profile. The rear surface obtained tokarnoy processing, provides good functional quality lenses, including the best moving and centering. When handling and turning are stable, rigid lens, through this lens treatment is not complicated and at low optical power.
Polymerization in form - lytъo (cast-mold)
Today this method is the most common. In mass production it allows you to make cheap enough soft contact lenses. First is form-matrix and punch. For each set of parameters made its own lens matrix. More on this matrix produce thousands of copies of plastic molds. The liquid monomer is poured into the lower half of a plastic shapes on top in this half inserted into the upper part of the form. Manufactured form ultraviolet radiation exposure. The result is a "dry" lens that is removed from the mold after rassoedynenyya.
The lens is saturated with water and subjected to further processing (chemical removal of the lenses of impurities, toning, sterilization, packaging and labeling). The production in this way silikonhidrohelevyh contact lens to improve wettability (decrease wettability angle) using various (including plasma) surface treatments of contact lenses.
In mass production have a high reproductive parameters of lenses produced by this technology.
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