So holding the index finger can ease the discomfort of a full bladder (too much water) and at the same time lubricate dry eyes (too little water).
The body is very clever at doing these balancing acts given a bit of help. So also with too much, or too little moisture in the hands and feet.
If you suffer from clammy hands and sweaty feet, then hold the index finger (either one) regularly throughout the day. This will also help teary eyes. Let me know if it works for you!