How is your hydration? I race enduros on my dirtbike and if I'm not good about my hydration and supplementation and let myself get dehydrated, my vision will get a little wonky, mostly lose the ability to change focus from far to near (when I go from looking down the trail to looking down to read my roll chart and timekeeping computer). Mostly happened when I first go into the sport before I read up on endurance supplements. Now that I add in electrolyte supplements, it's not happening anymore.