Chameleon, (Photo credit, somepets.com)
This week, as you probably guessed, I am going to inform you on Chameleon eyes. It is widely believed that chameleons can look in two different directions at the same time, well, this turns out be only partially true. Chameleons can scan their surroundings for danger or prey, but they cannot focus in two different directions. When they hunt, they must look at their prey with both eyes before striking. One thing that the chameleon has going for it are negative lens, meaning that the lens in their eyes are concave. This increases the retinal image size, allowing more precise focusing. In fact, image magnification in chameleons is higher in a scaled comparison than all other vertebrate’s eyes. While the lens is negative, the cornea is positive or convex. This also contributes to precise focusing by improving sight resolution in a narrower field of vision. When you think about it, Chameleons don’t really need long range vision. They usually live in an environment rich with bugs anyway, so they don’t need to look a long ways for their next meal. And let’s face it. They’re too slow to get out of the way of a swooping bird anyway.
To see some lizard with their eyes facing different directions, click here to watch my video.
Cat face (photo credit, photosof.org)
Now I’m going to focus on feline eyes. Cats, like dogs and many other animals, have a tapetum lucidum. Which is a reflective layer behind the retina that sends light passing through the retina back into the eye. While this improves the ability to see in darkness, it appears to reduce net visual acuity, thus detracting when light is abundant. In very bright light, the iris closes to a slit, reducing the amount of light on the sensitive retina, and improving depth perception. The tapetum and other mechanisms give the cat a minimum light detection threshold up to seven times lower than that of humans. Variation in color of cats’ eyes in flash photographs is largely due to the reflection of the flash by the tapetum. Cats have a visual field of view of about 200°, while humans only have 180°. But their binocular field (overlapping the images from each eye) is narrower than that of humans. As with most predators, their eyes face forward, affording depth perception at the expense of field of view. Field of view is largely dependent upon the placement of the eyes, but may also be related to the eye’s construction. Instead of the fovea, which gives humans sharp central vision, cats have a central band known as the visual streak. Cats can see some colors, and can tell the difference between red, blue and yellow lights, as well as between red and green lights. They are also able to distinguish between blues and violets better than between colors near the red end of the spectrum. I’ve noticed a “win some lose some” pattern with different kind of eyes, Humans can’t see well in the dark, cats can’t see all the colors, And chameleons can’t focus on two different things. But that’s for next week.
To see the inside of a cat’s eye, click here to watch my video.