Hide field only if prepopulated

I have two fields (Title and Category Post Field) that can either be filled in manually or get prepopulated, depending on which way (direct link or redirect from post) you get to the form.

I now would like to hide the two fields IF they get prepopulated. To set the visibility to Admin only won't help as it then is always hidden. Any ideas?

Thanks!

Thanks for your tip! This is how I solved it (code added to header.php):

[php]
<style>
<?php
  // get ref parameter from query string
  $ref_id = $_GET['ref'];
  // if the parameter has a value (which means it is a redirect from another page), hide certain fields
  if(isset($ref_id)){
    echo "#field_1_17,#field_1_18{display:none;}"; //
  }
?>
</style>