Why can a mouse see well in the dark with tiny eyes?
Yet other animals with bigger eyes (like us and horses) cant see in the dark very well?
But then owls and some lemurs have big eyes specifically to give them better night vision?
Answers:
The size of the eye is only important because larger eyes mean that more light can enter the eye. That is one of several adaptations that nocturnal animals have to increase their vision at night. To understand why this is important, you have to understand how vision works. Basically, most animals have both rods and cones. Cones are responsible for clear vision during the day, while rods are responsible for vision in low light and for peripheral vision. Having large eyes is good, because it allows more light to pass into the eye, but that's not good enough to have clear vision at night. Most of the light that passes into the eye does not hit a rod in the retina - instead it just passes through. This light is essentially wasted. In humans, for instance, only about 10% of the light that enters the eye falls on a photosensitive part of the retina, which accounts for our poor night vision. Many nocturnal animals have a layer behind the retina called the tapetum lucidum. At night, light enters the eye and hits the retina. Some of the light hits rods, but a lot of it doesn't, and this light passes through the retina, hits the tapetum lucidum, and is reflected back into the eye, where some of it hits rods. This increases the clarity of the animal's vision at night, and causes the eyeshine that you see in cats, dogs, deer, and other animals at night.
Hope that helps answer your question. Here are a few interesting websites that have more info:
http://en.wikipedia.org/wiki/tapetum_luc.
http://en.wikipedia.org/wiki/night_visio.
http://www.owls.org/information/eyesight.
It's all relative, how big would its eyes be if it was as big as you?
Mice and rats, and rodents in general, do not have good eyesight in the light or dark. They rely strongly on smell, and vibrations received by their vibrissae (whiskers).
The efficiency of any eye is dependent on the lens arrangement, and the number of light-receptor cells in the retina. The relative size of the retina also plays a large part in the sight process.
All this twaddle about cats being able to see in the dark; no animal can see in the dark. Some animals, cats included, have better low-light vision than others, but total-darkness to any animal equals blindness.
You can also get deeper into the sight discussion, and examine the hypothesis that dogs only see in black-and-white. Is that the eye that only responds to black-and-white, or is it the dog's brain cancelling the colour component as being unnecessary?
Tiny eyes? Watch this picture!
http://www.yesnet.yk.ca/schools/wes/proj.
Because they listen to their mothers unlike us and horses and eat all their carrots up like good little boys and girls
cause they are nocturnal
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But then owls and some lemurs have big eyes specifically to give them better night vision?
Answers:
The size of the eye is only important because larger eyes mean that more light can enter the eye. That is one of several adaptations that nocturnal animals have to increase their vision at night. To understand why this is important, you have to understand how vision works. Basically, most animals have both rods and cones. Cones are responsible for clear vision during the day, while rods are responsible for vision in low light and for peripheral vision. Having large eyes is good, because it allows more light to pass into the eye, but that's not good enough to have clear vision at night. Most of the light that passes into the eye does not hit a rod in the retina - instead it just passes through. This light is essentially wasted. In humans, for instance, only about 10% of the light that enters the eye falls on a photosensitive part of the retina, which accounts for our poor night vision. Many nocturnal animals have a layer behind the retina called the tapetum lucidum. At night, light enters the eye and hits the retina. Some of the light hits rods, but a lot of it doesn't, and this light passes through the retina, hits the tapetum lucidum, and is reflected back into the eye, where some of it hits rods. This increases the clarity of the animal's vision at night, and causes the eyeshine that you see in cats, dogs, deer, and other animals at night.
Hope that helps answer your question. Here are a few interesting websites that have more info:
http://en.wikipedia.org/wiki/tapetum_luc.
http://en.wikipedia.org/wiki/night_visio.
http://www.owls.org/information/eyesight.
It's all relative, how big would its eyes be if it was as big as you?
Mice and rats, and rodents in general, do not have good eyesight in the light or dark. They rely strongly on smell, and vibrations received by their vibrissae (whiskers).
The efficiency of any eye is dependent on the lens arrangement, and the number of light-receptor cells in the retina. The relative size of the retina also plays a large part in the sight process.
All this twaddle about cats being able to see in the dark; no animal can see in the dark. Some animals, cats included, have better low-light vision than others, but total-darkness to any animal equals blindness.
You can also get deeper into the sight discussion, and examine the hypothesis that dogs only see in black-and-white. Is that the eye that only responds to black-and-white, or is it the dog's brain cancelling the colour component as being unnecessary?
Tiny eyes? Watch this picture!
http://www.yesnet.yk.ca/schools/wes/proj.
Because they listen to their mothers unlike us and horses and eat all their carrots up like good little boys and girls
cause they are nocturnal
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