protected function addIop(\FlotChart $chart, models\Element_OphCiExamination_IntraocularPressure $iop, $timestamp, $side)
 {
     if ($reading = $iop->getReading($side)) {
         $seriesName = strtoupper($side[0]) . 'E';
         $chart->addPoint($seriesName, $timestamp, $reading, "{$reading} mmHg");
     }
 }