"Circle lenses" (also known are "Big eye" lenses) are an special type of cosmetic contact lenses first created and marketed in asian countries like Japan and South Korea. This lenses have something special about them: they can make your eyes look bigger.
To create the effect of a bigger eye, the diameter of the iris in the lenses is larger compared to ordinary cosmetic lenses. Some of them have a dark circle (limbal ring) around the iris, which helps making the eye look even bigger.

"Circle lenses" (también conocidos como "Big eye lenses" o "pupilentes agrandadores de pupila/ojo") son un tipo especial de lentes de contacto de tipo cosmético elaborados y comercializados por primera vez en países asiáticos como Japón y Corea del Sur. Estos lentes de contacto tienen algo especial: pueden hacer que tus ojos se vean más grandes.
Para crear el efecto de un ojo más grande, el diámetro del iris en estos contactos es incrementado en comparación con lentes de contacto ordinarios. Algunos de ellos tienen un anillo oscuro (anillo limbal) alrededor del iris, lo que ayuda a hacer que el ojo se vea aún más grande.

Here are some examples of how circle lenses look. You can easily see the difference:

Aquí hay algunos ejemplos de cómo se ven los circle lenses. La diferencia es muy notable:

Circle lenses exist in a wide variety of colors and prescriptions, and most of them last for a year. Common diameters for circle lenses go from 14.00 mm to 15.00 mm (15.00 mm giving the greatest enlarging effect).
Circle lenses have been approved by several health institutions in asia. They are safe to wear, but be sure to pay special attention to hygiene and only buy them from trusted sellers, since fake lenses are getting more common and those can damage your eyes. Popular brands are Geo and Dueba.

Since I'll be reviewing some pairs of circle lenses, I thought I should make a small post explaining what they are! I know they are quite popular know, but the're still unknown for a lot of people. I hope this can help clearing any doubts