This section is from the book "Holistic Medicine", by Shriniwas J. Kashalikar.
While a person is performing asana he is advised to adopt bhrumadhya dnshh (focusing ones eyes on the point between the two eyebrows), nasikagra drishh (focusing eyes on tip nose), or closure of the eyes The drishti presumably helps to integrate one's thinking with one's feelings, intuitions, passions etc At least, there is a subjective experience to this effect. This is important because many psychological disturbances are due to lack of such integration This effect mustbe studied carefully especially with due attention towards the concurrent neural input in optic nerves, activity of muscles of eye balls, neural activity in parietal cortex, occipital cortex and other related regions, activity in other body muscles and all other physico-physio-psycho-spiritual concomitants.
Dnshh puts in action certain muscles of eye ball and lets the others rest. The ones which are put in action are usually at rest and vice versa. This allows diversion of mind, from painful or disturbing or distressing issues Drishti is associated with calm expressions on the face and relaxation of the related muscles of face. This apparently helps the individual to break the vicious cycle of pain, anxiety causing wry face and / or wry expressions.
Another possible benefit of drishti is synergism between the two cerebral cortices which probably perform distinctly different but complementary functions, viz. intuitive and intellectual. The drishti apparently helps in differential relaxation of die body muscles, composure of the personality, concentration of the mind The value of stereopsosis is known in this connection.
As far as kriyas are concerned there are some difficulties in accepting and the conceding of the point of their safety Trataka and kapalbhati however, appear to be safe.
However, it is essential to avoid them in diseased states involving related organs.
The effect of kapalbhah seems to be in terms of reverting the gravitational effects without gross changes in the posture of the body.
Suryatrataka, agnitrataka etc however must be done by only under experts (with thorough scientific background as 111) guidance, in view of effects of U.V. and other, radiations. As regards vamanaknya, it may prove useful in cases of what is called ADHMANA.i e dyspepsia resulting from distension or hyperacidity. This is because vamana may assist the timely relaxation of lower esophageal sphincter in times needed.
Kriya, such as basb, helps, if used judiciously and with due precaution, in hygiene of bowel, especially in those who have constipation of functional nature.
Other kriyas such as involving cleaning of teeth, ears, mouth, tongue, eyes, nose, skin etc are obviously form important items in the daily routine and must continue to do so.