What is refraction? Which portions of the eye refract light before the light reaches the retina? How did these areas appear in the cow eye?

Refraction:

When ray of light passes through from one medium to another medium, due to the difference in medium index, the light deflect from its original path. This deflection of light ray from its path is called refraction. The phenomenon of refraction can also be observed in sound and water waves.

Cornea reflect the light before light reaches to the retina. Cornea is a transparent part and which place in front of the eye.

The irises of cow look brown that is why the eye of cow looks brown. But the irises of man can be different type like brown, green blue etc.