Keen Eye is an ability found in various animals of different types.
In Battle Use
Animals with the Keen Eye ability cannot have their accuracy lowered.
Out of Battle Use
Animals of lower levels will not be encountered when an animal with the Keen Eye ability is out of its aniball.
Keen Eye likely developed from animals with powerful visionary abilities likely from either spotting prey as a predator or using sight to scout out for oncoming predators.