A long time ago, my yoga instructor suggested this: Light a candle in a dark room, sit a few feet away from it and focus your eyes on it. Do not blink. After a

A long time ago, my yoga instructor suggested this: Light a candle in a dark room, sit a few feet away from it and focus your eyes on it. Do not blink. After a while, your eyes might start welling up but fight hard not to blink. On the mental level, do not think about anything. Just concentrate on your breathing and the light in front of you. Something like 5-10 mins should be fine in the initial stages. I haven't tried beyond that. Also, make sure you are decently hydrated throughout the day before starting on this exercise. Good luck.