Isomorphic controls could only be operated by one user. Such controls ostensibly worked only after identifying the allowed user through genetics or other uniquely identifying properties, such as their biological morphic field, of which the name "isomorphic" was derived from. One such device was 's laser screwdriver. The Tenth Doctor attempted to use it to overpower the Master, only to be ridiculed when he could not. (TV: Last of the Time Lords) Gwen Cooper lied to Rex Matheson that the Eye-5 contact lenses were isomorphic. (TV: Dead of Night)