6 facts you didn't know about whitetail deer vision Part 1 Number 6. A whitetail deer has a round eye but an oval, almost rectangular pupil. This shape reduces light from entering above and below and allows deer to have heightened vision horizontally, where most of their predators live. Huge advantage for treestand hunters. Number 5. Deer have larger pupils than humans. These larger pupils increase light gathering nine times more than humans. Which is exactly why they can see better under low li