Field Class Dependencies
One solution here is is to use template_preprocess_field function. In your template.php add a MYTHEME_preprocess_field function and perform a check on the node's field value to determine a class that you set in the classes_array variable.

function MYTHEME_preprocess_field(&amp;$variables) {
  $node = menu_get_object();

  //Add a new CSS class to field_MYHIDDEN_FIELD
  if($variables['element']['#field_name'] == 'field_MYHIDDEN_FIELD') {

    //Check field_MYCHECKED_FIELD for an empty value
    $new_class = (!isset($node-&gt;field_MYCHECKED_FIELD[LANGUAGE_NONE][0]['value'])) ? 'mytheme-field-novalue' : 'mytheme-field-value';
    $variables['classes_array'][] = $new_class;
  }
}