雅思场景听写训练 第24期:饮食与健康(1)（在线收听）

About four million people in the United States wear soft contact lenses. These lenses, made of water-absorbing plastic, were developed in the former Czechoslovakia and were introduced into the United States in 1964. The first soft lens was approved by the FDA in 1971. In recent years, soft lenses have become more popular than hard lenses. There are several reasons for this increasing popularity. Many wearers find the soft lenses more comfortable. Also, unlike the case with hard lenses, no break-in period is necessary for soft lenses. But there are drawbacks as well. The soft lenses cost more than the hard lenses. In addition, the life of soft lenses is often measured in months compared to years for hard lenses. They tear easily and become worn by handling. Also, soft contact lenses correct only a limited range of visual problems. Nevertheless, for those who can afford them, soft contact lenses are a safe, simple and attractive solution to the problem of poor vision.