IE11 javascript screen resolution

I've a strange situation. A simple code like this

<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="utf-8" />
        <title></title>
    <script>
        function checkScreen()
        {
            alert(window.screen.width);
            alert(window.screen.height);
        }
        checkScreen();
    </script>
    </head>
    <body>
    </body>
</html>

It works on all browser and it show to me my screen resolution (1920x1080) but, on IE 11 it show 1812x1029. After a search, I've not found nothing that can help me to understand why IE gets these values from js (it isn't even the viewport). If somehone can illuminate me on this situation it will be a great help. Thanks.