When you buying a new contact lenses, except duration and method of use, it is important to know what type of material is made. Besides the parameters you have been prescribed by your ophthalmologist, the material is the most important feature of the contact lenses, because it depends on how much the lens will be healthy and convenient to carry. Each human eye has different characteristics and needs, and it is particularly important to know what it's best for your eye.
To be a lens comfortable and pleasant to wear, should be made of material that contains water, which make the lens soft and comfortable, and allows passing of oxygen to the cornea, which is particularly important for the health of the eye.
Accordingly, the lenses are divided into several types:
- Impermeable PMMA contact lenses: tight or "hard" contact lenses are the first lenses are manufactured. First produced in 1960. The are made from a type of plastic called a PMMA (polymethyl methacrylate), a material that is very lasting, but it allows the flow of oxygen to the eye or the cornea. During the blinking lens displaced by allowing oxygen to reach the eye by the tears that touch the cornea. PMMA contact lenses can scratch the cornea of the eye if the lens is not really properly in the eye or if worn during sleep. Also this type of lens is much more likely to replace the cornea or can very easily fall out of the eye. This kind of lenses are least comfortable today already almost not used. However there is a number of people who prefer this type of lenses because of their durability and lower cost.
- Gas - permeable contact lenses: This type of contact lenses are also known as RGP. They are newer and more modern preparation of rigid lenses which are made of plastic in combination with several materials such as silicone and fluoropolymers that permit passing an oxygen directly through the lens to the eye. It is for this reason they are called gas-skip lenses.
- Soft contact lenses: These lenses are made of plastic materials together with water. This quality makes them soft and very flexible and also allow oxygen to reach the eye. Soft lenses can be hydrogel and silicone - hydrogel lenses. Hydrogel lenses are older type of soft contact lenses. Hydrogel has the ability to attract and retain water. These lenses containing from 55% to 75% water. Tears equally distributed and create a feeling of wet and comfortable lens. The problem with this type of soft lenses is that they have low permeability of oxygen and therefore inclined to damage. Silicone - hydrogel lenses are made by sophisticated technology. Contain a smaller proportion of water, from 25% to 50%, but have exceptional oxygen permeability of around five times more than the other soft lenses. Silicon is a waterproof material and problem for manufacturers is how to link the hydrophobic silicone with hydrophilic hydrogel to provide surface moisture required for comfortable wearing. The new silicon - hydrogel contact lenses manage to make a successful combination which allow a greater percentage of water and excellent oxygen permeability.