Saturday, November 19, 2011

Lions and Their Vision

As my Gentle Readers know, I have just gotten back from a safari in Africa.  I can't tell you in words about the impact that it has had on me as I am still digesting it.  I still am not totally on my sleep schedule yet and have been conking out at 8  pm or drinking lots of coffee so I fall asleep at 10 pm.

One of the things I have noticed is the difference in which animals see things.  On safari I saw lots of lions.  Lions are big in Tanzania.  In fact, the Broadway hit, "Lion King"  went over big here.  All the Tanzanians know Accoona Mattata -- No problem. 
I learned some interesting things about lions and vision.

Apparently, lions have some of the best binocular vision of all the species.  In fact, they have practically perfect binocular vision.   Biologists have noted that predators overall have the best binocular vision of all the animals.  Unlike prey animals, like zebra, a lion has its eyes square in the middle of its head.    Although there are tradeoffs in gaining great binocular vision.  A lion's visual field is compromised in favor of better depth perception and binocular vision in lions that comes with relatively narrowly placed eyes, that aid them in judging distance from prey for pouncing upon it.   This means that a lion can't see as much of the world around it as a zebra can but it is better able to judge distance so that it can pounce better.

The visual axes in a lion's eye are roughly parallel.  With parallel visual axes, the maculae of the retina can align on the same object.  The macula is oval-shaped highly pigmented yellow spot near the center of the retina that contain special light-sensitive cells. In the macula these light-sensitive cells help lions and other mammals including man see details clearly in the center of a visual field.

In the daytime, Lions see about as well as humans dowhile at night their vision is at least six times better than ours.   In fact, I was warned to stay in my tent when we were camping out in the Serengetti as lions were known to roam through our campsite.  The lions could see us before we could see them.  For some reason, lions didn't like to go in the tents so I was safe in the tent. 

In a lion's eye, there are more rod cells than cone cells in the retina of the eye. These are photoreceptor (light-sensetive) cells, cone cells being colour sensitive and rod cells are light-sensitive. Lions having more light sensitive cells packed tightly in the fovea (most sensitive area of the retina), this means they only need 1/6th of the light that humans need to see in.

Another reason  lions can see better than we can is because of a special eye structure known as a “tapetum lucidum,” (Latin translation of "bright carpet") which absorbs and reflects the available light.   The tapetum lucidem is the  reflective layer of cells positioned behind the retina. This means that light entering the eye will be absorbed by either the rod or cone cells, light that passes through the retina and the photoreceptor cells is reflected back by the Tapitum lucidum and the light-sensitive cells have a second chance to absorb the light waves, in effect doubling the effectiveness of their night vision

This structure is what gives lions (and all cats) the unique glow, eyeshine,  that can be seen if light is shined at them in the darkness.  

In bright light, a lion's pupils constrict to round points so the lion can hunt during the day without being blinded by the sun. At night, their hunting ability is enhanced because the pupils of their eyes let in more light by dilating to three times the size of a human’s pupils.  Like many cats, a lion's pupil reacts quicker to changes in light than that of dogs.

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