Functionally, there are myopia glasses, reading glasses, astigmatism glasses, anti-sand glasses, sunglasses, anti-ultraviolet glasses, welding glasses, anti-infrared glasses and so on. According to the types of materials: glass mirror, resin mirror, plexiglass mirror, etc. From the appearance: there are full frame, half frame and hidden type. Contact lenses are widely used to correct ametropia. They are about the size of buttons, thin and completely transparent. Divided into soft mirror and hard mirror. The soft lens is made of 2- hydroxyethyl methacrylate, which is soft and can absorb water, and it is soft and comfortable to wear, but it is easy to deform and break, so it is not suitable for astigmatism eyes. The hard lens is made of methyl methacrylate, which is hard and difficult to deform, and is suitable for correcting high astigmatism and keratoconus. Contact lenses have some features that ordinary glasses don't have, mainly including: (1) Because contact lenses are close to the cornea and can rotate with the rotation of the eyeball, no matter which direction, light can always enter the eye through the center of the lens, thus eliminating the prism effect and oblique astigmatism caused by the edge of ordinary glasses. (2) Irregular astigmatism on the corneal surface is effectively eliminated. The curvature of contact lens surface can be specially ground according to refractive requirements to replace the irregular curvature of corneal surface, thus eliminating corneal astigmatism. (3) Contact lenses can eliminate the size difference between eyes. Because it is close to the cornea, the image on the retina after the light passes through is similar to that without glasses, and the object will not be enlarged or reduced, especially for a person with anisometropia or aphakia in one eye. (4) Contact lenses are light and thin, stick to the surface of cornea, and have beautiful appearance, which is especially suitable for actors, athletes and other special occupations. However, those suffering from keratitis, corneal ulcer, corneal epithelial exfoliation and pannus should not wear contact lenses, and those suffering from acute conjunctivitis and dacryocystitis are prohibited from wearing contact lenses. Therefore, not everyone with myopia can wear contact lenses. Types of contact lenses According to the manufacturing materials, contact lenses can be roughly divided into soft contact lenses and hard contact lenses. As the name implies, soft contact lenses are made of soft materials, so contact lenses can be very close to the cornea, and the foreign body sensation is very small, which makes people almost forget its existence. On the contrary, hard contact lenses are hard and will not deform along the cornea, so the foreign body sensation is heavier. Contact lens materials to evaluate the quality of contact lens materials, oxygen permeability is an important goal, because to maintain the health of the cornea, there must be sufficient oxygen supply. The higher the oxygen permeability of the material, the higher the water content, so sometimes the water content is used to represent the oxygen permeability. Therefore, the higher the water content, the better the oxygen supply is usually. Attractive advantages of soft contact lenses: short adaptation period, more comfortable wearing, good stability, and can be worn intermittently at any time. Disadvantages: poor optics, easy to break, easy to deposit, difficult to clean, short life (1-2 years), relatively causing conjunctivitis and high infection rate. Characteristics and advantages of hard contact lenses: good optics, good astigmatism correction effect, long service life (3-5 years), easy cleaning and low infection rate; Disadvantages: long adaptation period, heavy foreign body feeling, large slip, easy to shift, afraid of sandstorm. Although hard contact lenses have their own advantages and disadvantages, hard contact lenses are healthier for glasses health care. Contact lenses are in direct contact with eyes, and the cornea has the greatest influence. To keep the cornea healthy, we must first have enough oxygen. Oxygen is mainly supplied by air and tears. Contact lenses form a barrier between air and cornea, which hinders oxygen supply and causes corneal hypoxia. One way to solve this problem is to increase oxygen permeability. In addition, there is a thin layer of tears between the contact lens and the cornea. Every time you blink, there will be some tears exchange, so that the tears with high oxygen content outside will run between the contact lens and the cornea, providing fresh oxygen to the cornea. But this tear exchange rate is only 2% for soft contact lenses and 20% for hard contact lenses. This is the reason why corneal hypoxia is not easy to occur under the same oxygen permeability. Moreover, soft contact lenses are larger (about 14mm) and hard contact lenses are smaller (about 9- 10mm). In terms of area, hard contact lenses are less likely to cause corneal hypoxia. The clinical benefits of hard contact lenses are good for cornea, and hard contact lenses have clinical benefits. Because of its large degree of sliding, if there is any damage to the cornea, the foreign body sensation will not get heavier and it can't be worn any more; Unlike soft contact lenses, the initial symptoms are not obvious, and when they can't stand it, they are already very serious. Although hard contact lenses have many advantages, their popularity is far lower than that of soft contact lenses. The biggest reason is that hard contact lenses have a long adaptation period and a heavy sense of foreign body, which some people simply can't stand. Disposable contact lenses Disposable contact lenses are basically soft contact lenses, but the service life of the products is short (from sun-throwing type to moon-throwing type). This is an improvement on the shortcoming that soft contact lenses are easy to absorb impurities. Because there is no need to consider the service life, the materials used in them are usually high in oxygen permeability and thin in thickness, and because of frequent replacement, impurities are not easy to remain, so they will not cause inflammation. But it has a big disadvantage, that is, it is very expensive to use. There is also a kind of contact lens called long wear type, which is also a high oxygen permeability material. It is said that it can be worn to sleep. But from the point of view of ophthalmologists, it is not recommended to wear this kind of contact lens, because according to statistics, the infection rate of sleeping with it is ten times that of cleaning every day. Therefore, even if you buy contact lenses that you wear for a long time, please take them off for cleaning and disinfection before going to bed every day to protect your mind window. Each kind of contact lens has its own advantages and disadvantages, and none of them is the best. In addition to the contact lens itself, personal physique, eye condition, wearing habits, lifestyle, working environment, etc. may affect the choice of contact lenses. Instructions for selecting contact lenses 1. No matter what kind of contact lens, the lens that can suit the individual is the best lens.