using get_avatar as filter

My theme uses a call back function inside wp_list_comments to display comments. The callback function mytheme_comments is inside functions.php and it displays avatars like this:

echo get_avatar( $comment, 44 );

I want to add a function inside my child theme which changes the avatar size to 60px only for comments. I do not want to edit or copy the whole comment callback function. So my guess is that I can do this using get_avatar filter but I don’t know how. Can someone please help?