Declared var in php page cannot be seen in function ?

[eL_NiNo]

Probably an easy problem, but can't figure it out for some reasons !

I have a PHP page in hich i declared a var called $strAction. Now, this var can't be seen in a function of this page (well, it should be visible as a global scope for this page, no ?).

Anyway here's the code :

$strAction = '';
function IsEnabled()
{
    if( $strAction == 'lookup' || $strAction == 'delete') // Line X
        return ' disabled ';
    else
        return '';
}

...

Notice: Undefined variable: strAction in page.php on line X