system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:how do we determine how good an animal’s eyesight is? And how do we compare it to our own or another animals?
gpt
There are a variety of studies that can be done. Some are observational. You see an eagle swoop down from one thousand feet high to catch prey and you have to assume it was able to visually detect the prey from that distance. Lab tests can be run in a similar fashion, putting something desirable at various distances away and recording how far or close the animal has to be to notice it.

You can also learn stuff by analyzing the eye itself via dissection. Like humans, other animals have rods and cones in their retinas, and scientists can observe the density and types of these structures to get an understanding of what types of light an animal might be able to detect and how well. For example, nocturnal animals will typically have more rods and fewer cones to adapt to low-light vision. Meanwhile, the aforementioned eagle's eyes have a larger variety of cones compared to humans, indicating that they see differences of color much more precisely than humans which helps detect prey at long distances.