【Popular Science Tips on Polymers and Materials】--33 The polymer materials hidden in \"contact lenses\" + People watching the sea

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Contact lenses, also known as corneal contact lenses, are lenses that are worn on the cornea of the eye to correct vision or protect the eyes. Based on the hardness of the material, it includes three types: hard, semi-hard, and soft. Contact lenses bring significant improvements to patients with refractive errors such as myopia, hyperopia, and astigmatism, not only in terms of appearance and convenience. It also offers a wide field of view and realistic image quality; furthermore, it plays a significant role in controlling the progression of myopia and astigmatism in adolescents, as well as in treating certain eye diseases. Hospital experts advise that those who wish to wear contact lenses should go to a reputable hospital or optical shop for a thorough examination, so as to choose the right type of contact lenses for themselves. It is also important to maintain good eye hygiene to prevent other eye problems; if any discomfort occurs after wearing the lenses, one should seek medical attention promptly. Materials: silicone hydrogels, hydrated polymers (methyl methacrylate, hydroxyethyl methacrylate, methyl methacrylate, etc.). Water content: The level of water content affects the properties of the lenses. The higher the water content, the softer the lens; however, it is also more prone to deformation and damage, and loses water more easily ； Conversely, the lower the water content, the better the moldability of the lens, with less deformation; it is also less likely to experience dehydration compared to lenses with a higher water content. The levels of water content are generally classified as follows: lenses with a water content of less than 38% are considered low-water-content lenses, those with a water content of 42%-60% are medium-water-content lenses, and those with a water content greater than 60% are high-water-content lenses. Oxygen permeability: For those who are wearing contact lenses or colored contact lenses for the first time, discomfort may occur, and one possible reason for this is oxygen deficiency in the cornea. Under normal circumstances, our cornea needs to be able to \"breathe.\" The oxygen permeability of contact lenses is an important indicator for assessing the quality of lens materials; therefore, a high oxygen permeability in the lens material is a crucial factor when choosing lenses. Prolonged hypoxia in the cornea can lead to various complications such as chronic corneal edema and corneal neovascularization. Contact lenses, especially colored contact lenses, meet the needs of those who are interested in maintaining their appearance, but it is essential to choose the appropriate contact lens product through proper fitting procedures and to follow strict care routines on a daily basis. It is important to note that lenses made of different materials, such as ordinary hydrogel lenses and silicone hydrogel lenses, have significant differences in their oxygen permeability, which in turn results in substantial differences in the duration for which they can be worn. For example, the new generation of Dr. Brown PureVision silicone hydrogel lenses have an oxygen permeability five times that of regular hydrogel lenses; this helps to prevent corneal hypoxia caused by prolonged wear of contact lenses, allowing for extended periods of continuous wear while still meeting the needs of taking short naps. Material history? (1) Rigid lens: PMMA polymethyl methacrylate was invented in 1934 ； The first all-plastic contact lenses were made from PMMA in 1947. Advantages: Good vision correction, longer lens lifespan ； Disadvantages: brittle, poor breathability, strong sense of foreign body. (2) Soft lenses: PHEMA, hydroxyethyl methacrylate, was discovered in 1960 ； The first pair of soft contact lenses was created (the father of soft lenses: Otto Wichterle) ； Approved by the FDA in 1971. Advantages: Soft, oxygen-permeable, comfortable, no feeling of foreign objects ； Disadvantages: Prone to adsorption and precipitation, short lifespan. (3) Gas-permeable rigid lenses (RGP): Developed in 1970, with Polycon obtaining a patent in 1972; the material is primarily made by copolymerizing PMMA and silicon. Advantages: Good oxygen permeability, lower hardness compared to PMMA ； Disadvantage: Lacks comfort.