How does animals see, is it black and white for a dog? Why are some animals blind?

Answer 1

Different animals use different senses, depending on what their survival dictates. Animals living deep in caves, for example, live in a world completely devoid of light, so their eyes did not have an environment in which that sense would have provided an advantage to their livelihood.

Similarly, an animal with a strong chemical sense (taste, smell) would not need strong eyesight (such as a dog).

The specifics of sight varies between species, however some basic principles are simple.

When light enters an eye, it strikes a structure in the back called the retina. The retina contains two types of nerve cells: rods, and cones. Rods contain a chemical that, upon contact with most light, generates an electrical signal that goes to the brain. Cones contain chemicals that, upon contact with lights of a specific color(s), send a series of electrical signal to the brain, the specific pattern of those signals being determined by the color of the light. In other words, cones are what allow your brain to understand color.

Rods are much more sensitive to low amounts of light. An animal that replaced all of its cones with rods would have very good vision, even in low amounts of light. Most nocturnal animals have no cones, but plenty of rods. They see better in the dark, but they can't see in color.

Cones need more light to generate an electrical signal strong enough for the brain to notice. An animal that replaced all of its rods with cones would have very sharp, detailed color vision, but would be blind in the dark. Most diurnal animals have only cones (birds are the most commonly cited animals).

Behind the retina is a structure known as the choroid. For most animals, this captures stray light that fails to strike a cell in the retina. Nocturnal animals have a slight evolutionary change that makes the choroid reflective, allowing light to bounce back into the eye. Because such light passes through the retina again, there's essentially a "second chance" to have that light detected. If the light passes through again, it travels out of the eye, which is why you sometimes see nocturnal animals with "shiny eyes." It's all that light being reflected back out.

You can always cause this effect in other animals by shining too much light for the choroid to absorb; in photography, we call this effect "red eye."

Answer 2

well eagles for instance actually have more accute eyesight than we humans do...dogs and cats do see colour but not as well. I just learnt too that cats don't actually see any better in the dark than humans do, however they use their whiskers and hearing to determine their position. Animals such as humans and apes need sight mostly to survive so our other senses aren't so strong. Sight is most important for scanning vast areas of terrain which is why most dessert or grassland animals have good eyesight. Animals that are blind or close to blind just don't need sight, their other senses are just so good that sight isn;t required for survival.

Answer 3

In general, animals that are blind evolved that way over time because it wasn't neccesary for them to have eyes that work. Animals that live underground, in caves, underwater, etc often don't need their eyes to navigate themselves.
An dogs don't see in black and white, they are color blind in the way humans are, mixing up reds and greens.

Answer 4

Dogs and cats don't see in black and white, they just don't see colours as well as we do.

As the first answerer said, not all animals require vision to live. Not as many are blind as people think tho - bats are not, they just have poor vision. They rely on echolocation instead. Owls are also not blind, they just rely more on their hearing.

http://en.wikipedia.org/wiki/Dogs#Sight
http://en.wikipedia.org/wiki/Eye

Chalice