Circle contact lenses come in a variety of colors and effects, and are a new fashion trend in Japan, Korea and Taiwan that make one's eyes appear larger. The diameter of regular contact lenses that are sold in America are on average 14mm - 16mm, similar to the diameter of the cosmetic circle contact lenses. The only difference is that circle contact lenses appear to be bigger because they are tinted not only in areas that cover the iris of the eye, but also prominently in the extra-wide outer rim of the lens. The result is the appearance of a bigger, wider iris. Circle contact lenses only change the color of your iris and will not affect your vision. The optical zone in the middle is transparent and it is large enough to provide clear vision.
The lenses are popular among Asian teenagers and young adults. The lenses create an illusion of large, doll-like eyes. Many people consider circle lenses as a fashion accessory rather than medical devices. They are used to create a look reminiscent of anime characters. They are also used to create the Kawaii look, which is characterized by large eyes with anime-like features or the Ulzzang look.In Asia, circle contact lenses can be bought in some stores. They can be purchased without a prescription (0.00 or plano or with prescription). Their legality in western nations varies with the local laws and in the United States they are currently classified as a medical device and are not legal for sale without a valid prescription. 
Along with this popularity, issues concerning the quality of these lenses have arisen. Currently, there are still companies selling circle contact lenses without bearing the stamp of approval from health services. Many lenses are manufactured in Asian countries where there are no guidelines or supervision over the production of the lenses.
The trend had spread to the United States, Australia and Canada, driven by Lady Gaga's video for her song Bad Romance, in which she displayed larger-than-life eyes. The New York Times noted that circle lenses were being worn around the country and were readily available in cosmetic and prescription variants on the Internet.
- from Wikipedia