Why use a white circle/spot in eye icons/logos?
What is the reason behind using a white circle/spot in eye icon/logo in terms of visual or graphic design? Is there any specific meaning?
The circle (or otherwise white mark) is a meant to be a reflection.
The reflection makes it more realistic and understandable as an icon. As seen in a google image search, our eyes are pretty reflective and we often perceive this even if we don't consciously think about it. As Andrew H notes, this reflection is called a catch light. Below is one for example:
For comparison take a look at these two icons below. I'd argue that the one with the dot looks more human like and friendly.