system
Given the following post, respond as if you're commenting on Reddit:
human
Is there a reason why bigger animals tend to have bigger eyes. What advantage is it having eyes in proportion to body size?
gpt
Bigger eyes generally mean better visual resolution and better light-gathering abilities.  It's basically the same reason that big telescopes are better than small ones.  For example, on the reef at dawn and dusk big predators come out to hunt.  They have the advantage over small reef fish because their larger eyes allow them to see better in the dim light.  

So big animals basically just have bigger eyes because they _can_.  You couldn't stick a human sized eye on a mouse, because the poor thing would be about half eyeball.  But there are diminishing returns, and eyeball size levels off.  Cows are a lot bigger than people, but their eyes aren't all that much bigger.  The animal with the largest eye of all, the giant squid, hunts in deep dark water and needs extra-large eyes to see.  The much larger blue whale has smaller eyes, due to the fact that it doesn't rely on vision, especially vision in dark water, nearly as much.