Meditation  is often practiced with eyes closed. But it can also be done with  eyes half-open and focused within, by following a well guarded  technique of yogi-s and tantric-s, called Shambhavi mudra.
Literally,  the word ‘mudra’,  means, seal, sign, badge, symbolic gestures or parched grain, in  different contexts. However in esoteric practices, it has a specific  meaning and relevance, associated with worship, dancing, postures or  mindful attention. Shambhavi mudra is a divine method of gazing inward to remove mental distractions, of  sojourning into the depths of one’s being with internalized  attention, and of opening oneself to nature’s higher forces.
This mudra is named after Shambhavi or Parvati (sometime identified as Durga),  the consort of Lord Shiva. Shambhavi symbolizing Shakti, the divine  energy, propels existence. Her manifestation in the human being is  best realized through this mudra,  which rests on the praxis of identity between the macrocosm and  microcosm.
Shakti  lies dormant at the base of the spine in the four-petalled psychic  centre (chakra), muladhara( mula = root; adhara = support). In its awakened state, it moves through sushumna nadi,  conduit of Shambhavi shakti, as mentioned by Svatmarama yogi in his  14th  century work, Hathayoga  pradipika ( IV.18). It  pierces the subtle centres – svadhishthana,  manipura, anahata,vishuddha and ajna – one after another till it unites with Shiva in the sahasrara  chakra , the thousand petalled lotus in the cerebral cavity. Svadhishthana  chakra lies at the root of reproductive organ, manipura,  in the region of the navel,  anahata, in  the region of the heart, vishuddha,  at the base of  throat, and ajna,  between the eyebrows. Shambhavi also connotes the aperture in the  crown of the head through which the self is believed to escape at the  time of death.
According  to Hathayoga  Pradipika ( IV.36), Shambhavi mudra has  three characteristics. The practitioner (sadhaka)  is inwardly attentive to Brahman, the supreme reality. He is able to harmonize the mind and prana, the  vital energy. And  finally, he  keeps the sight steady in a way that he appears to see everything,  while in reality, he sees nothing outside, below or above.
The  beginner may gaze on the tip of the nose, or fix the sight on  something external like a speck of light, a black dot on white, or a  natural object like the sun, moon or star, without blinking  ((trataka).  But advanced seekers concentrate on the space between eyebrows by  rolling both eyes upwards. With practice, gazing becomes involuntary,  and one experiences union with the Supreme Being (samadhi)  spontaneously. Even when eyes are closed, the sadhaka is  able to watch the object of focus in the inner space of his mind  (chidakasha).
 Shambhavi mudra is best practiced under the guidance of a guru in siddhasana ( perfect pose) or padmasana (lotus  pose), with jnana  mudra - the posture of hand placed on knees, in which the tip of thumb is  touched with the tip of  index finger. This is accompanied by  rhythmic breathing (pranayama),  contemplation on the Absolute reality (brahman)  and chanting of the primal sound, AUM ( manasa  japa).
The sadhaka undergoes a variety of experiences, depending on the rate of progress  made in this mudra.  He may see the sun, stars, galaxies or concentric rings of violet or  yellow, or feel as if he has landed in a paradise of beauty, light  and bliss. His breath slows down. Sometime he loses physical  consciousness for a short while, and undergoes involuntary body  movements. 
‘Whatever  wonderful shunya (void) or ashunya (not void) is perceived, is to be regarded as the manifestation of  that great Shambhu ( Shiva), states Hathayoga  pradipika (  IV.36).
Shambhavi mudra vivifies the physical, the vital, the mental and the intellectual  sheaths (kosha-s)  in the subtle human body (sukshma  sharira),  by internalizing consciousness flowing in mundane objects. As eyes,  called the windows of the mind, stabilize, the vagaries of chitta,  mind-stuff, are curbed automatically, and the pineal gland activated,  with an increased level of awareness. When the active and passive  aspects of the Supreme Reality, ie Shakti and Shiva respectively,  coalesce within, the third eye of sadhaka is opened. 
 Shambhavi mudra increases the alpha brain waves, boosting creativity and  concentration. It takes away depression and cures insomnia. Yogi-s,  tantrika-s and siddha–s keep this mudra secret in accordance with the injunction in Hathayoga  pradipika ( IV.340) which treats Shambhavi  mudra as the one which is secluded like a respectable lady, in contrast to  an ordinary woman. The Gheranda  Samhita ( III.60), a late 17th  century Vaishnava treatise on yoga, corroborates this view. The one  who is accomplished in Shambhavi mudra is called the living embodiment of  divinity (brahmarupa). 
 About Author:  Dr Satish K Kapoor, former British Council Scholar and former  Registrar, DAV University, is a noted author, educationist,  historian, and spiritualist based in Jalandhar City.
 This piece was first  published and is courtesy The Tribune, Chandigarh.
 For a very good site  on Mudras visit http://www.mudravigyan.com/Mudra.html There is a lot to learn from this site by Shri Bansal. It has  pictures and guidelines for mudras to improve eyesight, energy  levels, prana and so on.