Can't use Raycast to detect if I look at object

I have tv with 3 buttons and 3 screens. Each button disable all screens and then enable it's own screen. Button is empty GP with the box collider only. I want to use a Raycast to detect when I look at Button1, Button2 or Button3. And after pressing LMB I want to enable one of 3 screens. But my code doesn't work...

 public GameObject screen1;
 public GameObject screen2;
 public GameObject screen3;

 private Collider thisCollider;
 private int channelNumber;

 void Start ()
 {
     thisCollider = GetComponent<Collider>();
 }
 
 void Update ()
 {
     if (Input.GetButton("Fire1"))
         if (DoPlayerLookAtButton())
             ChangeChannel();
 }

 bool DoPlayerLookAtButton()
 {
     RaycastHit _hit;
     Ray _ray = Camera.main.ScreenPointToRay(new Vector3(Screen.width / 2, Screen.height / 2, 0));
     bool isHit = Physics.Raycast(_ray, out _hit, 1.5f);
     
     if (isHit && _hit.collider == thisCollider) // with the second condition it doesn't work
     {
         switch (thisCollider.name)
         {
             case "Button1": channelNumber = 1; break;
             case "Button2": channelNumber = 2; break;
             case "Button3": channelNumber = 3; break;
             default: break;
         }
         return true;
     }
     else
         return false;
 }

 void ChangeChannel()
 {
     DisableAllScreens();
     switch (channelNumber)
     {
         case 1: screen1.SetActive(true); break;
         case 2: screen2.SetActive(true); break;
         case 3: screen3.SetActive(true); break;
         default: break;
     }
 }

 void DisableAllScreens()
 {
     screen1.SetActive(false);
     screen2.SetActive(false);
     screen3.SetActive(false);
 }