Comment author user id

Im trying to get comment authors user id how do i do that?

Here is the comment autput code im trying to manipulate and get comment authors user id from.

function get_comment_author( $comment_ID = 0 ) {
	$comment = get_comment( $comment_ID );

	if ( empty( $comment->comment_author ) ) {
		if ( $comment->user_id && $user = get_userdata( $comment->user_id ) )
			$author = $user->display_name;		
		else
			$author = __('Anonymous');
	} else {
		$author = $comment->comment_author;
		echo $id;
	}