Colour Vision: Humans are trichromatic, meaning they can perceive three primary colours (red, green, and blue). This trait allows us to distinguish a wide range of colours. In comparison, many mammals, such as dogs, cats, and cows, are dichromats, meaning they only have two types of cone photoreceptor cells in their retinas. As a result, they are less capable of distinguishing between certain colours, such as red and green. However, some other animals, like primates and some birds, have trichromatic or even tetrachromatic (four-colour) vision, allowing them to perceive colours in ways that humans can't.
Resolution and Acuity: Humans have a relatively high visual acuity, which means we can see fine details clearly. This is facilitated by the high density of cone photoreceptor cells in the central part of our retinas, called the macula. Some birds of prey, such as eagles, have even higher visual acuity, enabling them to spot small prey from great distances. Other animals, such as cats, have lower acuity but excel in low-light conditions due to having a higher proportion of rod photoreceptor cells, which are more sensitive to dim light.
Peripheral Vision: Humans have a wide field of view, allowing us to see a large area without moving our eyes. However, some animals, like rabbits and horses, have even wider fields of view, giving them a better sense of their surroundings.
Night Vision: Humans have limited night vision compared to many animals. This is because humans have a relatively small number of rod photoreceptor cells compared to other species. Animals like cats, owls, and raccoons have a higher proportion of rods, allowing them to see better in low-light conditions. Some animals, such as geckos and snakes, even have specialised structures in their eyes that enhance night vision further.
Motion Detection: Many animals have specialised visual adaptations for detecting motion. For example, certain lizards and insects have specialised neurons that respond specifically to movement. These adaptations help these animals locate prey or avoid predators.
It's worth noting that even within the same species, there can be variations in eyesight based on factors such as genetics and individual adaptations.