How Is the Eye of a Cow Different From the Eye of the Human?

Human eyeballs and cow eyeballs are structurally similar in many ways. Both human and cow eyeballs have the sclera, or white part of the eyeball, cornea or clear structure over the iris and pupil, lens, vitreous fluid, retina and choroid. The choroid is the layer of the eyeball that lies between the retina and the sclera. It supplies blood to the retina. The differences lie in the size of the eyeball, the tapetum lucidum (reflective quality) in the cow eye, the ability to discriminate colors, visual clarity and the functional advantages for each species in its environment.

  1. Size of the Eyeball

    • According to the Journal of Experimental Biology, the radius of the average cow eyeball is 15 mm. This translates into a diameter of 30 mm. Sources vary on the size of the average human eyeball, but the general consensus is 24 mm. All of the anatomical structures of the eyeball that cow and human eyes share in common are larger in the cow eyeball.

    Tapetum Lucidum

    • Anytime an animal, such as a cow, is seen looking into automobile headlights or into the flash of a camera, its eyes appear to be glowing. The anatomical structure that causes a cow's eye to reflect light in that way is the tapetum lucidum. The tapetum lucidum is an area of chartreuse pigment that is located just below the retina at the level of the choroid, in the back of the cow eyeball. This structure causes light that enters the eye to reflect within the eye and amplify low levels of light to improve the cow's night vision. This structure is not present in human eyes.

    Color Discrimination

    • Cows do not see in only black and white. However, the distribution of rod and cone cells in the cow's retina does not allow them to perceive colors in the same way that human beings do. No one can describe accurately how cows see colors, but the distribution of the rod and cone cells in the retina indicate that they can discriminate, on a less precise level than humans, between colors such as red and green, blue and yellow, and of course black and white.

    Visual Clarity

    • The tapetum lucidum functions to increase the cow's night vision ability. However, the internal light reflection that it causes can result in loss of visual clarity during the daytime. Again, it is difficult to put the vision of a cow in terms of 20/20 because they cannot talk to us. However, microscopic evaluation of the retina and visual system of a cow suggests that the cow's eye is capable of seeing at a level that could correspond with approximately 20/80 in the daytime.

    Functional Advantages for Each Species

    • We human beings rely on our sharp, clear daytime vision to allow us to function in our world. Cows do not require clear vision to find food sources and water. They need good night vision and the ability to detect the motion of a potential predator. Their eyes are designed well for this. The rod and cone cell distribution in the cow eye causes them to sacrifice visual clarity compared to humans, but they gain an increased ability to see motion at night, which helps them survive in their habitat.