How do I detect when the mouse is outside a specific area of the screen?

Let's say I have an invisible 2D circle at the center of the screen and has a radius of 200 pixels. When the mouse is inside this circle, nothing happens, but when the mouse is outside this circle, I want an object to, for example, look at where the mouse's position translated to world space. How would I go about doing that? Can anyone point me in the right direction? Are there any particular resources I could refer to?

 

Code (csharp):

1.  
2. if (Vector2.Distance(input.mousePosition, center) < radius) {
3.     // Mouse is inside the circle with the center and radius.
4. }
5. else {
6.     // Mouse is outside the circle area
7. }
8.  

 

I can't believe I forgot about .Distance(), thanks!

 

Another option (just for the record here) is to use the IPointerEnter/Exit handlers.