Tantra, probably the most all inclusive spiritual system ever developed and the root of yoga, utilizes trataka on a wide scale in its many practices, whether using symbolic diagrams, deities or objects as a focus of worship or awareness. Trataka in one form or another is utilized by almost every religious and spiritual system, though often heavily disguised. In Hinduism, an integral part of the religious practice is to sit in front of a picture or a statue of Krishna, Rama, Shiva, the symbol Aum and so on. Though many will regard this as a form of worship, and of course it can be if the worshipper is sincere, it is actually a form of trataka for the aim is to concentrate the mind on the external deity. From this comes mental peace and a meditative state. Further-more, many Hindus have the ability to create at will internal visualizations of the outer objects and perform inner trataka.
In Christianity the same thing is done, though in a less obvious manner. In a church there are idols of Christ, there are candles and there is always the symbolic cross. These objects act as focal points for trataka, though of course it is not known by this name. All of these forms have a deep-rooted symbolic meaning which generally acts below the level of normal awareness. In other words, these symbols correlate with and stimulate experiences and memory that is contained in what Jung called the collective unconscious. Therefore these objects of awareness invoke experiences and knowledge of which you are normally unaware.
In Tibetan Buddhism, trataka is often done on various deities, on Buddha and various geometrical figures known as yantras or mandalas. Even Zen Buddhism utilizes trataka, though possibly of a more abstract type, such as staring at a blank wall. The practice of trataka is not confined to yoga. It is universal and has been used throughout the ages as a method of transcending normal experience. Trataka is simple, yet very powerful and this is the reason why so many different systems and religions have used it in one form or another as a means for spiritual upliftment.