The composition and manufacturing of contact lenses
The means of contact correction are a great way to correct vision defects without compromising yourself in the usual joys of life. Lenses provide visual acuity and, unlike corrective glasses, do not limit the clarity of peripheral vision. Soft contact lenses do not need to be corrected, removed during sports, swimming, and other activities. Every year they become more and more popular.
Evolution of SCL production technology
The field of contact vision correction is constantly evolving. Constant experiments, new technologies, improvement of materials, and composition of the lens- these are what the best specialists of the leading optical companies are doing. Modern SCL and contact devices, for example, were radically different from each other fifteen years: the material, the main characteristics, and the method of production.
Before the world first learned about contact correction, many scientists around the world were working to create vision-enhancing devices. The first attempts to create something similar to lenses are attributed to the greatest scientist and artist, Leonardo Da Vinci. His lens was a clear glass globe filled with water, through which the objects he examined seemed larger.
A century later, Rene Descartes created his lens. It was a long thin tube, also filled with water, with a magnifying glass attached to it on one side; the other end of the tube was "in contact" with the eye.
In 1888, the first analogs of modern SCL appeared. The glass device itself is kept on the eye, but it completely covers the eyeball, causing discomfort.
In the 40s of the twentieth century, the first lenses made of hard plastic were created. They were much smaller than their predecessors in size, but the material was uncomfortable to wear and sometimes even could injure the eye.
The real revolution in the industry of contact correction occurred in the early 50s of the last century. Two Czech scientists, Otto Wichterlem and Dragoslav Limom, managed to synthesize a completely new material, where 38% of the lens' own mass was water. Thanks to the water component, a soft polymer was obtained – the material for the first-ever elastic contact devices.
What are the contact lenses made of today?
The development of contact correction is now based mainly on the improvement of the properties of the lens.
Depending on the main polymer, there are two groups of SCL in the composition:
The first type is produced from a special polymer-hydrogel, the main component of which is water (from 38% to 69%). The higher the moisture content is, the softer and more delicate the lens material will be. The company of Bausch + Lomb released hydrogel one-day SCL with a rate of water of 78%!
Silicone-hydrogel lenses consist of two polymers-hydrogel and silicone. Unlike hydrogel lenses, this type of lens is not only soft; it is "breathable." The constant flow of oxygen to the cornea has a positive effect on the duration of wearing, and also makes it possible to sleep in the lenses. Some models can be worn for up to 30 days without removing.
What are tinted contact lenses made of?
Tinted contact lenses, as well as corrective ones, are made of hydrogel or silicone hydrogel. The peculiarity of modern tinted lenses is a layer of pigment sealed in the middle of the lens, which changes the color of the eye or shades it. This pigment is hypoallergenic and safe because it does not contact directly with the cornea and even the eyelid.
Due to this additional layer, the colored and tinted lenses are thicker than conventional ones. Therefore you can wear them for up to 8 hours, and the carnival ones only for 2-4 hours.
Production technologies of modern contact lenses
In the modern branch of SCL production, there are several basic technologies:
- centrifugal formation;
- casting method
- mixed method.
This is the technology that formed the basis for the creation of the first hydrogel contact devices in 1960 (Prague Institute of molecular chemistry). It is still used today. The essence of the method is that a certain mass of the liquid substance, rotating at high speed, gradually solidifies and acquires the desired configuration.
First, a liquid monomer is placed in a special curved form. Rotating, the monomer is affected by centrifugal forces. Thanks to a specially set temperature, it spreads in the right proportions in shape. Gradually, the material hardens and is converted into a solid polymer.
After hardening, the polymer can be saturated with an aqueous component. Next, the passage of mandatory computer photo control: checking the size, material, quality of polishing, etc. The next stage is sterilization at high temperatures, tinting, sealed packaging in blisters, and boxes.
The peculiarity of the lenses, which were produced by the centrifugal formation method, is the aspherical back surface.
This method is used for the production of both hard and soft materials. The solid monomer falls on a special machine with computer control. Preset programs affect the workpiece in such a way that the result is contact lenses with different specified parameters.
After that, the machine is subjected to lens polishing. The next stage is hydration, deep chemical cleaning, quality control, tinting (if necessary), sterilization. Unlike centrifugal forming, the turning method is several times more expensive.
It is quite an expensive method of production. First, you need to cast a matrix of metal (personal for each new set of lenses). The forms-copies are created according to the matrix where the monomer is poured.
The strongest action of ultraviolet rays on the monomer forms solid billets. After hardening, they are sent for polishing, then saturated with an aqueous component. The next steps are toning, quality control, sterilization, and packaging in blisters.
The method of pressing
This method is used less often than others. The hardened polymer billets are pressed in special molds, followed by a hydration process. The reverse production option is possible: first, the solid polymer is enriched with water, and then pressed.
It is a quite popular and effective way to create SCL. The front surface of the lens is created by centrifugal forming, and the rear part- by turning.
This method is the basis for the creation of the most complex optical devices.