Limit rotation on x & y axis

I’m working on a project where a set of eyes rotate towards the cameras current position. However, I would like to limit the movement of the eyes on the x & y axis as I am trying to make the eye movement look as natural as possible. Thank you for your time.

If you want to limit rotation inside a cone (same angle from the center in any direction), use Vector3.Angle to know the angle relative to the eye forward direction - for instance:

var maxAngle: float = 15;

private var fwdDir: Vector3;

function Start(){
  fwdDir = transform.forward; // save initial forward direction
}

function Update(){
  // find direction to camera
  var dir: Vector3 = Camera.main.transform.position - transform.position;
  // if camera inside viewing angle, follow it:
  if (Vector3.Angle(dir, fwdDir) < maxAngle){
    transform.forward = dir;
  }
}