Light Theory
Light waves change speed when they cross a boundary between 2 densities such as air and glass this causes them to change direction. This is called refraction.
When the eye sees the image It sees it upside down but the eye transfers it to the brain which causes it to be the right way up. Light from the object is bent by the cornea. The lens does some adjustments and bends it further and finely focuses it light is focusly sharpened on the macula by the retina
The spectrum of light is range of wavelengths of radiation which is electromagnetic and that causes our eyes to be delicate.