Third Eye

Gaara creates an eye out of sand that hovers in the air wherever it's created. Gaara connects the eye with his optic nerve using chakra, allowing him to see whatever is in the Third Eye's field of vision. The eye gives Gaara a useful method of performing surveillance without being noticed; in Sakura Hiden, Gaara manipulates the Third Eye's sand to allow it to double as a listening device. Gaara also uses the Third Eye when fully surrounding himself with the Shield of Sand, allowing him to be protected without sacrificing seeing what opponents are doing.

In Gaara Hiden, Gaara is capable of creating several eyes and connect each of them to his optical nerve at once, allowing him to observe things from multiple angles simultaneously.

Rasa makes his Third Eye out of Gold Dust. Rasa, like Gaara, must close one of his eyes before he can see through the Third Eye. In the anime, Shinki has displayed the ability of creating multiple Third Eyes with his Iron Sand, without the need of closing one of his, though it quickly drains his chakra.

Trivia

 * In Buddhism and Hinduism, the third eye is considered to be the eye of knowledge and symbolises enlightenment, some deities being depicted with it.
 * In Naruto: Shippūden episode 410, the eye is depicted as blue, matching Gaara's eye colour.