A Comparison Between a Human's and Cow's Eye

Aim

To compare the structure of the cow's eye to the structure of a human eye

Materials

Cow's eye

Sharp Knife

Plastic dishes

Paper Towel

Tweezers

Mounted Needle

Hypothesis

My hypothesis is that we should be able to see all the parts of a human eye (that we've been studying from the text book) in the cow's eye. This is my hypothesis because just from my knowledge, I think cow's need to see as well as humans do. They need to see what they are eating, where they are going, and since all mammals are somewhat related, their eye functions should be relatively similar to each other. I don't think evolution changed the functions of eyeball in mammals that differently to each other. We all live in similar environment and we all use eyes for the same purpose.

The Exterior of the Eye

A table comparing the exterior of the eyeball in cows and humans

Optic Nerve

It looks exactly like in the text book, except that I think that the white 'wall' or 'membrane' surrounding the nerve fibers in the pig was thicker; I could hardly see the nerve fibers.

Pupil

The shape of the pupil in cow's are oval. Humans are round. When strong light passed the pupil of the cow's eye, it appeared to be blue colour! Humans are only black.

Sclera

They appear to be the same. (The cow's sclera is so thick to break through!)

Iris

When I looked around at my colleague's eyeball cow, all the iris seemed to be dark brown. I know that human's iris come in different colour such as green, blue, gray, etc.

Cornea

They look exactly the same

Exterior Observations - A diagram illustrating the shape of Cornea, Iris and Pupil

Description of Cow's Eyeball's Shape

The two eyeballs (cows and humans) look very similar. The cow's eyeball seemed to be almost round (excluding the cornea section). The cornea always seemed to be the part that was 'sticking out' of the eyeball.

Function for Muscles

The muscles and pieces of fat were attached to the thick sclera of the eyeball. The muscles were thick and fat. The function of the muscles there are to move the eyeball around so that you can have full vision around your eye, not just in front. The muscles are there in order to move your eyeball around your socket.

The Interior of the Eye

A diagram from the inside back half of the dissected eyeball

Diagram of the inside front half of the dissected eyeball

Lens

The cow's lens seem to be exactly the same as the human lens. When I examined the lens, and I put it up close to an image, it almost worked as a magnifying glass. BUt when I put it up to an image with a distance, the image turned up side down. This proves that our eyeball (more like our retina) 'sees' images up side down, and that our brain converts the image the right way around for us.

Vitreous Humour

The vitreous humour was jelly-like, and clear. It filled up most of the interior eyball, and didn't squirt out when I stabbed the eyeball with the knife. The vitreous humour looks like mucus, but isn't sticky. This humour helps to fill and give the eyeball it's shape.

Analysis

Prefer eyes facing front or side? Table of disadvantage and advantage of eyes on sides and front

Eyes on front

Advantage - You can see in front of you without turning your whole head to one side. Also, take an example of a lion. Eyes in front of them help them watch their prey and judge how far they are.

Disadvantage - You don't have a wide range of vision as eyes on the sides of your head

Eyes on sides

Advantage - You have a very wide range of vision. Take an example of a horse: their vision are almost up to 350 degrees! This helps them so that they can see if there are any lion-like hunters sneaking back at them from behind.

Disadvantage - Sometimes in order to see something well in front of you, you need to turn your whole head to the side. You ever watched a cow eating?? It turns their head to the side!

A Cow Colour Blind or Not?

I can tell from the eyeball that the cow is not colour blind. The back of the eyeball (from the inside) has many colours. This is caused by cones which containing different pigments. Humans normally have 3 pigments collecting blue, yellow-green and green, the abillity seeing different colours. In cows, as we've dissected, we can see that it has many pigments, therefore it must not be colour blind.

Conclusion

My hypothesis was correct, that a cow's eye and human's eye are very similar. I think that the major difference was only the shape of the pupil. We have all the functions like cow's, except their eyes a lot bigger than our eyes. Now that I know how strong and tough the scela is, next time I will cut the muscles around it freely (I wasted so much time seperating the muscles because I thought the scerla was thinner). A cow is slow and wouldn't have time to turn it's whole head 180 degrees just to see if there's a lion behind it. That's another advantage of having eyes on the sides of your head. I was able to compare the illustration from the text-book and make connections. I was able to dissect the cow's eyeball and draw conclusion and justify to my observations, like the colour-blindness.