As regards trataka, it is steady gazing at a particular point or object without winking of the eyes. There are 5 types of trataka:
Central horizontal: keep a candle flame three to four feet away from your body. The level of your eyes and the candle flame should be in a horizontal line. Sit straight, with relaxed body. For one minute, look upon the flame with a steady gaze and without winking. After a minute, close the eyes, relax the eye muscles, and visualize the flame between the eyebrows for a minute. Then again gaze with open eyes on the flame for a while and then relax and close the eyes. Continue this for five to six minutes. Slowly increase the period of gazing from one to three minutes, spending equal time relaxing the eyes.
Vama Jatru Trataka and Dakshina Jatru Tratak: These are left shoulder and right shoulder gaze. Sit in any comfortable posture. Sit straight, head steady and neck straight. Keep the thumb in front of you and fix the eyes on the nail of your thumb. Slowly move the hands towards the end of your shoulder, keeping yur eyes fixed on the thumb nail-eyes wide open - no turning of the head. Maintain the gaze without flickering eyelids. Now, repeat this exercise for the other shoulder. Cup your hands and cover them over your closed eyes for rest, each time. Note:Make use of the right thumb for left shoulder and the left thumb for the right shoulder.
Bhrumadhya Drishti (Frontal Gazing): Start concentrating by directing and turning the half-closed eyes towards the space between the eyebrows. Do it slowly.
Nasagra Drishti (Nasal Gaze): Sit in a comfortable position with body relaxed and gaze at the tip of the nose for one or two minutes.
CAUTION: One should avoid too much strain on the eye muscles while practising any of the above trataka. If you feel any pain or tiredness, close the eyes and relax the eyes muscles. Prolonged practice without the guidance of a qualified yoga practitioner may affect the eye muscles as well as the nervous system.
In the beginning practise for a minute or two and gradually increase to ten minutes, but should without any strain.