Follow mouse only at certain angle?

Hey, I can’t work out how to do this, but this is what I have so far…

onClipEvent (enterFrame) {
radians = Math.atan2(_root._ymouse-this._y, _root._xmouse-this._x);
degrees = (radians/Math.PI)*180;
_rotation = degrees;
}

How would I make it so that it can only point between 0 and 90 degrees? Thanks.