How to not show a comments field if user logged in
Use hook_form_alter():

/**
 * Implements hook_form_alter().
 */
function my_module_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  global $user;
  if ($form_id == 'comment_form' &amp;&amp; $user-&gt;uid != 0) {
    $form['field_email']['#access'] = FALSE;
  }
}