Trāṭaka
the Haṭha Yoga Pradīpikā
Gazing at a mark without blinking.
- The text tells the practitioner to look steadily at a small mark until the eyes water, and then to close them.
- Candle-flame gazing is the commonest modern form, and the tool has it.
Sources: Haṭha Yoga Pradīpikā 2.31