The value of pupillary dilation in pre-emptive analgesia: is there more to this than meets the eye?

The pupillary dilatation reflex may present an objective method of predicting whether sedated patients require additional analgesia for painful procedures. Behavioural pain assessment tools identify pain only once it has occurred and are unable to guide pre-emptive management. The pupillary dilatation reflex response to a tetanic stimulus has been utilised to assess analgesic requirements in patients under anaesthesia and for those with postoperative pain. This tool appears promising to assess pain in the critically ill; however, a number of questions remain unanswered regarding the influence of sedation on this response. These questions require further exploration before the pupillary dilatation reflex can be widely adopted into clinical practice.