add WxH dimensions to WP Retina 2x plugin's column

function addtoretinacolumn_wh_value( $column_name, $id ) {
$meta = wp_get_attachment_metadata($id);
if(isset($meta['width']) && $column_name == 'Retina')
echo $meta['width'].' x '.$meta['height'];
}
add_action( 'manage_media_custom_column', 'addtoretinacolumn_wh_value', 10, 2 );