If ones eyes are constantly watching sexual movies, magazines, etc. it would be considered zina of the eyes. If one goes to the place to commit zina or to the place of sexual movies, magazines, etc., it would be considered zina of the feet. Similarly, the act of masturbation, could be considered a zina of the eyes, or hands, etc.
The Prophet (blessings and peace of Allah be upon him) explained the seven sins that doom a person to Hell in a saheeh hadeeth that was narrated by the two Shaykhs, al-Bukhaari and Muslim, in as-Saheehayn, in which it was narrated that the Prophet (blessings and peace of Allah be upon him) said: “Avoid the seven sins that doom a person to Hell.” We said: What are they, O Messenger of Allah?