In recent years, the use of soft contact lenses has been expanding, but most consumers do not have a detailed understanding of the material, design and technology of soft contact lenses. Currently, there are two types of soft contact lens lenses on the market, one is the traditional one. HEMA water gel (HEMA water gel also has many kinds of subdivided materials, most of which will focus on the water content ratio), the higher the water content of the traditional hydrogel lens, the higher the oxygen permeability will be, up to 70 % water content and oxygen permeability value can be as high as DK25~30.
However, this kind of high water content lens must also be used by people with sufficient tear secretion, because if the tears are not enough to replenish the moisture required by the lens, the lens will have insufficient water retention, resulting in foreign body sensation, dry eyes, red eyes or oxygen permeability. The effect may not be ideal, leading to hypoxia and hyperplasia of blood vessels. Overdry lenses may even rub against the surface of the cornea, endangering eye health. Moreover, lenses with too high water content are less stable. In addition, it is relatively easy to break.
Silicone Hydrogel (that is, hydrogel + silicon Si) ("silicon" is actually used in high oxygen permeability hard contact lenses is quite popular today, mainly because of its ultra-high oxygen permeability. .) However, due to the limitations of the material, it is impossible to use silicon alone to make contact lenses (silicon is a water-repellent material, which has poor hydrophilicity), so it combines the components of hydrogel and silicon with advanced technology to achieve comfort and high transparency. Oxygen balance.
The biggest advantage of silicone hydrogel contact lenses is that they can use low water content while achieving high oxygen permeability. We just mentioned that the oxygen permeability of traditional hydrogels is about DK25~30, but most silicone hydrogels are oxygen permeable. It can further reach DK 100 or more, and can use low water content to avoid the trouble of insufficient tears or the inability to replenish the moisture required by the lens, achieve long-term wearing, and avoid hypoxia problems.
But there are also disadvantages. Although it is a soft lens, it is slightly harder and has a certain thickness, so the foreign body sensation is heavier when worn at the initial stage. More attention must be paid to the cleaning of the lens. Because the main feature of silicone hydrogel is high oxygen permeability, it is not easy to be infected. In cleaning and maintenance, special attention must be paid to the cleaning of tear protein and oil, and pay attention to the potions purchased. Not all potions can be used, because some of the maintenance liquids PHMB containing small molecules, then these small molecules will be attached to the pores of the silicone hydrogel while preserving the lens. These small molecules will damage the corneal epithelial cells and cause severe corneal damage, bacterial infection, and corneal infiltration Symptoms and more.
So generally speaking, the material properties of silicone hydrogel are excellent, but you still have to try to see if you can accept the comfort of the product, and still pay attention to cleanliness and hygiene to avoid infection.
(Text / Optometrist Huang Qunchen)