Occasionally Over The Last Couple Years During Strenuous Exercise, I

occasionally over the last couple years during strenuous exercise, i feel a pulling sensation on left eye as if it's crossed, this goes on for a few seconds, sight is out of focus then restores and no other symptoms. I always thought it was dehydration, but lately it has occurred more often, and when i don't seem to be dehydrated. For example it happened today, and i had eaten a normal breakfast a few hours before and had consumed water. I should say that i have been working out more often which is why i believe it to have happened more often, though one day it happened i was sitting in a meeting, no strain whatsoever. I am expericing a lot of stress in my life at the moment. trying to rule things out.