Daniela Ruah, the actress who has played Kensi Blye on CBS show NCIS: Los Angeles since 2009, does not have a glass eye. Ruah has a birthmark (clinically known as a Nevus of Ota) in the iris of her right eye, making the eye color appear black. The natural color of her left eye is hazel.
Birthmarks in the eye are rare, but often very noticeable since the eyes are in such a prominent facial position. Such birthmarks are usually harmless, although discoloration of some body tissues can sometimes indicate an underlying serious condition. The birthmark in Ruah's right eye has no effect on her vision.