NeurOptics | Pupillometry in Critical Care
pupillometry in critical care
constriction velocity, critical care, critical care nursing, intraocular pressure, modified rankin scale, neurocritical care, neurologist, neuroscience nursing, neurosurgeon, NIH Stroke Scoring Scale, NIHSS
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Trending Pupil Size and Reactivity in the

Critical Care Patient

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Pupil Examination is a Standard of Care

The clinical neurological exam is a cornerstone of providing care to patients with a wide variety of neurological and neurosurgical injuries (11,15,16,21). Clinicians have been assessing the pupils of patients with suspected or known brain injury or impaired consciousness for over 100 years (14). Today, clinicians routinely evaluate pupils as a component of the neurological exam and monitoring of critically ill patients with neuronal injuries, including patients with traumatic brain injury and stroke (15,16,18,21,31). The American Association of Neurological Surgeons and the Brain Trauma Foundation Guidelines for Management and Prognosis of Severe Traumatic Brain Injury (4) recommend that pupillary light response should be evaluated and used as a prognostic parameter and that pupil dynamics and asymmetry should be documented in the clinical record.  The pupillary response is also used with the National Institutes of Health Stroke Scale (NIHSS), a systematic assessment tool that provides a quantitative measure of stroke-related neurologic deficit (20). The scale is widely used as a clinical assessment tool to evaluate acuity of stroke patients, determine appropriate treatment, and predict patient outcome.

Pupillary Evaluation Is Important to Patient Care and Outcome

Studies have shown the importance of pupillary evaluation in the clinical setting. Scientific literature provides much evidence that alterations of the pupil light reflex, size of the pupil, or anisocoria, are correlated with outcome of patients with traumatic brain injury (2,3,4,5,6,7,12,17,24,25,27,28). Pupillary information is used clinically as an indication for possible surgical intervention. Anisocoria (unequal pupils), especially if the disparity is greater than 1 mm, can indicate a pathological process or a neurological dysfunction. A unilaterally dilated, sluggishly reactive or non-reactive pupil can suggest transtentorial herniation and compression of the third cranial nerve (CN III) (9,15) and has been proposed as a prognostic indicator of functional recovery after traumatic transtentorial herniation (1,23,25). In addition to herniation and third nerve compression, it has been shown through blood flow imaging that pupil changes are highly correlated with, and can be used for monitoring brainstem oxygenation and perfusion (24,27,32).


Many investigators have used pupil size and reactivity as the fundamental parameters of more general outcome predictive models in conjunction with other clinical information such as age, mechanism of injury and Glasgow Coma Scale (16,19,32) and correlated such models with the presence and the location of intracranial mass lesions (5).


It has also been shown that, depending on pupillary status, neurosurgeons triage patients into conservative therapy or surgical evacuation of mass lesions (16,21,23,25,28). Patients that undergo prompt intervention, such as surgery or hyperosmolar therapy, after a new finding of pupil abnormality have a better chance of recovery (7).

Manual Pupil Assessment is Highly Subjective and Inaccurate

Traditionally, pupil measurements have been performed in a very subjective manner by using a penlight or flashlight to manually evaluate pupil reactivity and using a pupil gauge to subjectively estimate pupil size. Common terminology employed in the clinical literature to describe the pupil light reflex and pupil size includes “unilateral” or “bilateral non-reactive pupils,” “fixed” or “dilated pupils”, as well as “brisk”, “sluggish” and “non-reactive pupils”. These are all subjective terms applied without a standard clinical protocol or definition and yielding, in fact, a pronounced level of inter-examiner variability and error (8,10,12,13,18,30).


Manual pupillary assessment as part of the clinical examination is subject to compounded sources of inaccuracies and inconsistencies and is characterized by high degrees of inter-examiner variability (11,13,18,21,22,26,30,31). A variety of factors can affect the validity of the visual assessment of the pupil and increase inter-examiner disagreement. These factors may include poor lighting conditions in the patient’s room, the examiner’s visual acuity, and the strength, distance and orientation of the light stimulus with respect to the patient’s eye (26,30). Studies have shown inter-examiner disagreement in the manual evaluation of pupillary reaction to be as high as 39% (8,18,22,26). A recent study revealed that critical care and neurosurgical nurses consistently underestimated pupil size, were unable to identify anisocoria, and incorrectly assessed pupil reactivity (11). This same study concluded that automated pupillometry is a necessary tool for accuracy and consistency in pupil measurement and that it might allow earlier detection of subtle pupil changes, allowing more effective and timely diagnostic and treatment interventions (11).

Automated Pupillometry is Reliable and Eliminates Subjectivity

The NeurOptics® NPi®-200 Pupillometer is a hand held portable infrared device that provides a reliable and objective measurement of pupillary size, symmetry, and reactivity through measurement of the pupillary light reflex. The numeric scale of the Neurological Pupil index (NPi®) allows a much more rigorous interpretation and classification of the pupil response. The Pupillometer and the NPi scale provide objectivity in measurement by comparing the patient’s pupillary light reflex to normative data in the NPi model. By automatically deriving whether the pupil reflex falls within the normal range (“brisk”) or outside of the normal range (“sluggish”, “atypical or non-reactive”), the pupillometer provides a reliable and effective way to quantitatively classify and trend the pupil light response (3,8,18,21). The optional barcode scanner and SmartGuard Reader allow automated patient identification entry and upload of data to the electronic medical record.


In summary, pupil evaluation is a critical component in the assessment and management of critically ill patients with neuronal injury. Manual pupil measurements are characterized by high inter-examiner variability and error. Automated pupillometry and the objective scale of the NPi benefit clinicians and patients by removing subjectivity from the pupillary evaluation, providing more accurate and trendable pupil data, and allowing earlier detection of changes for more timely patient treatment.

Pupillometry Results in Improved Quality of Neurological Exam

Assessment of pupil size and reactivity is a fundamental aspect of the neurological examination. However, manual pupil assessments (using a penlight or flashlight) are subjective and fraught with a high degree of inter-examiner variability (22,26). In a recent study from The University of Texas Southwestern Medical Center, two examiners, under identical conditions, simultaneously evaluated the left and right pupils of consented patients. Over 2,320 paired exams were performed by neurology and neurosurgery attending and resident physicians, staff nurses and mid-level practitioners. The study showed low interrater reliability when performing manual pupillary examination (22,26). Automated pupillometry provides completely accurate, reliable and objective pupil data, independent of examiner, resulting in a significant quality improvement for this important component of the neurological examination.

Bibliography and Links to Abstracts

1. Andrews BT, Pitts LH: Functional recovery after traumatic transtentorial herniation. Neurosurgery, 29:227-31, 1991.
2. Braakman R, Gelpke GJ, Habbema JD, Maas AI, Minderhoud JM: Systematic selection of prognostic features in patients with severe head injury. Neurosurgery, 6:362-370, 1980.
3. Chen JW, Gombart ZJ, Rogers S. Gardiner SK, Cecil S, Bullock R: Pupillary reactivity as an early indicator of increased intracranial pressure: The introduction of the neurological pupil index. Surg Neurol Int; 2:82, 2011.

4. Chesnut RM, Ghajar J, Maas AI, Marion DW, Servadei F, Teasdale GM, et al. Management and prognosis of severe traumatic brain injury. Part II: Early indicators of prognosis in severe traumatic brain injury. Brain Trauma Foundation, American Association of Neurological Surgeons, Joint section on neurotrauma and critical care. 41:54, 2000.

5. Chesnut RM, Gautille T, Blunt BA, Klauber MR, Marshall LF: The localizing value of asymmetry in pupillary size in severe head injury: relation to lesion type and location. Neurosurgery, 34:840-846, 1994.

6. Choi SC, Narayan RK, Anderson RL, Ward JD: Enhanced specificity of prognosis in severe head injury. J Neurosurgery, 69:381-385, 1988.

7. Clusmann H, Schaller C, Schramm J: Fixed and dilated pupils after trauma, stroke, and previous intracranial surgery: Management and outcome. J Neurol Neurosurg Psychiatry, 71(2):175-181, 2001.

8. Du R, Meeker M, Bacchetti P, Larson MD, Holland MC, Manley GT: Evaluation of the portable infrared pupillometer. Neurosurgery, 57: 198-203, 2005.

9. Goebert HW Jr: Head injury associated with a dilated pupil. Surg Clin North Am 50:427- 432, 1970.

10. Hults KN, Knowlton SL, Oliver JW, Wolfson T, Gamst A: A study of pupillary assessment in outpatient neurosurgical clinics. J Neurosci Nurs, 38(6):447-52, 2006.

11. Kerr RG, Bacon AM, Baker LL, Gehrke JS, Hahn KD, Lillegraven CL, Renner CH, Spilman SK: Underestimation of pupil size by critical care and neurosurgical nurses. American Journal of Critical Care, 25 (3), 213-219, 2016. doi: 10.4037/ajcc2016554

12. Levin HS, Gary HE Jr, Eisenberg HM, Ruff RM, Barth JT, Kreutzer J, High WM Jr, Portman S, Foulkes MA, Jane JA, Marmarou A, Marshall LF: Neurobehavioral outcome 1 year after severe head injury. Experience of the Traumatic Coma Data Bank. J Neurosurgery, 73(5):699-709, 1990.

13. Litvan I, Saposnik G, Maurino J, Gonzales L, Saizar R, Sica REP, Bartko JJ: Pupillary diameter assessment: Need for a graded scale. Neurology, 54:530-531, 2000.

14. Loewenfeld IE, Lowenstein O: The pupil. Anatomy, Physiology, and Clinical Applications. Wayne State University Press, Detroit, 1993. No longer in print.

15. Manley GT, Larson MD: Infrared pupillometry during uncal herniation. J Neurosurgical Anesthesiology, 14:223-228, 2002.

16. Marmarou A, Lu J, Butcher I, McHugh GS, Murray GD, Steyerberg EW, Mushkudiani NA, Choi S, Maas AIR: Prognostic value of the Glasgow Coma Scale and pupil reactivity in traumatic brain injury assessed pre-hospital and on enrollment: An IMPACT analysis. J Neurotrauma, 24(2): 270-280, 2007.

17. Marshall LF, Gautille T, Klauber M, Eisenberg HM, Jane JA, Luerssen TG, Marmarou A, Foulkes MA: The outcome of severe closed head injury. J Neurosurgery, 75: 28-36, 1991.

18. Meeker M, Du R, Bacchetti P, Privitera CM, Larson MD, Holland MC, Manley GT: Pupil examination: Validity and clinical utility of an automated pupillometer. J Neurosci Nurs, 37(1):34-40, 2005.

19. Narayan RK, Greenberg RP, Miller JD, Enas GG, Choi SC, Kishore PR, Selhorst JB, Lutz HA, Becker DP: A comparative analysis of the clinical examination, multimodality evoked potentials, CT scanning, and intracranial pressure. J Neurosurgery, 54(6):751-762, 1981.

20. NIH Stroke Scale (NIHSS).

21. Olson DM, Fishel M: The use of automated pupillometry in critical care. Critical Care Nursing Clinics North America, 28 (2016), 101-107, 2015. Doi: 10.1016/j.cnc.2015.09.003

22. Olson DM, Stutzman S, Saju C, Wilson M, Zhao W, Aiyagari V: Interrater reliability of pupillary assessments. Neurocritical Care, 2015. Doi: 10.1007/s12028-015-0182-1

23. Petridis AK, Dörner L, Doukas A, Eifrig S, Barth H, Mehdorn M: Acute subdural hematoma in the elderly; clinical and CT factors influencing the surgical treatment decision. Cen Eur Neurosurg., 70(2):73-78, 2009.

24. Ritter AM, Muizelaar JP, Barnes T, Choi S, Fatouros P, Ward J, Bullock MR: Brain stem blood flow, pupillary response, and outcome in patients with severe head injuries. Neurosurgery, 44(5):941-948, 1999.

25. Sakas DE, Bullock MR, Teasdale GM: One-year outcome following craniotomy for traumatic hematoma in patients with fixed dilated pupils. J Neurosurgery, 82(6):961-965, 1995.

26. Stutzman S, Olson DM, Saju C, Wilson M, Aiyagari V. Interrater reliability of pupillary assessments among physicians and nurses. Department of Neurology and Neurotherapeutics and Neurological Surgery. UT Southwestern Medical Center, 2014 Neurocritical Care Society Poster presentation ahead of publication.

27. Taylor WR, Chen JW, Meltzer H, Gennarelli TA, Kelbch C, Knowlton S, Richardson J, Lutch MJ, Farin A, Hults KN, Marshall LF: Quantitative pupillometry, a new technology: Normative data and preliminary observations in patients with acute head injury. J Neurosurgery, 98(1):205-213, 2003.

28. Tien HC, Cunha JRF, Wu SN, Chughtai T, Tremblay LN, Brenneman FD, Rizoli SB: Do trauma patients with a Glasgow Coma Scale score of 3 and bilateral fixed and dilated pupils have any chance of survival. J Trauma, 60:274-278, 2006.

29. Wilkie, A: Nursing time savings study: Pupillary assessment times. Poster presentation, 2015.

30. Wilson SF, Amling JK, Floyd SD, McNair ND: Determining interrater reliability of nurses’ assessments of pupillary size and reaction. J Neurosci Nurs 20:189-192, 1988.

31. Worthley LIG: The pupillary light reflex in the critically ill patient. Critical Care and Resuscitation, 2:7, 2000.

32. Zhao D, Weil MW, Tang W, Klouche K, Wann SR: Pupil diameter and light reaction during cardiac arrest and resuscitation. Crit Care Med, 4(29):825–828, 2001.

Why measure the pupils of a critically ill or injured patient?

Frequent pupil evaluation is part of the protocol for care of the critically injured or ill patient. The pupillary light reflex (PLR) and pupil size have traditionally been used as a clinical parameter and as a prognostic indicator. The Brain Trauma Foundation and the American Association of Neurological Surgeons recommends that pupillary light reflex for each eye should be used as a prognostic parameter and that the duration of pupillary dilation and fixation should be documented. In addition to use on patients with neuronal injury, the pupillometer can facilitate measurement of pupil dynamics on patients who are under the effect of recreational drugs or medications prescribed for medical treatment – such as analgesics, sedatives, and anesthetic agents. Certain drugs or medications have an effect on pupil size, often making manual assessment challenging and potentially inaccurate.

How is this assessment currently done?

Currently, this assessment is manually performed by clinicians using a penlight/flashlight and pupil gauge (Haab scale(citation)). Terms such as “brisk”, “sluggish”, “minimally reactive” or “non reactive” are used to describe reactivity resulting in a very subjective and qualitative measurement.


The American Association of Critical-Care Nurses (AACN) Procedure Manual for High Acuity, Progressive and Critical Care features a new section on pupillometry, noting that the pupillary examination is a key assessment performed during neurological examinations and guiding nurses on the use of automated pupillometers.

The new edition of the American Association of Neuroscience Nurses (AANN) Core Curriculum for Neuroscience Nursing includes a new section on automated pupillary assessment, which states that use of a pupillometer removes measurement subjectivity and provides a way to track and trend pupillary reactivity in a consistent, objective, and quantifiable way.

Nursing Time Saved

Automated pupil assessments have been shown to decrease nursing workload associated with time spent per assessment every 1-2 hours (29). As critical care nursing leadership looks to improve efficiency in critical care unit staffing, Pupillometers at each bedside can assist in that effort. Click on the line below:

Click Here for Time Saving Example
Nursing Time Saved: Automated vs. Manual Pupil Assessment

Manual Pupil Assessment Technique

Manual pupil assessments (penlight) are subjective and fraught with a high degree of inter-examiner variability. It is well documented that automated pupillary assessment solves these problems, but manual pupil assessment can also take more time than automated pupillometry and little has been discussed about this.

A paired assessment with the pupillometer takes a clinician about 15 seconds. Manual pupil assessment can be confounded by several issues: Visual acuity of the examiner, dark eyes or small pupils of the patient, ambient light conditions and the subjectivity and skill/experience level of the examiner. As a result, in some patients, a clinician will often pass the penlight multiple times to try and confirm what he/she sees and a manual assessment can take even more time. In other cases, if the clinician is not sure, or if there is a suspected pupil change, another opinion might be sought. This involves an additional person and several minutes more of time. As a single measurement, these differences might not seem meaningful but given the frequency of pupil exams, these differences are significant over time.

Charting and Inputting Data
Some clinicians will complete the exam and immediately record the pupil measurement data into the terminal, while others will complete the pupil exam, continue with necessary patient care, and then later go to the terminal, log in, input the data and log out. Nurses at a high volume neuro ICU were recently timed and, on average, these charting and data entry steps took about one minute. Automatic data upload will eliminate the need to manually chart and input data.

Annual Cost Savings Example

Utilization of pupillometry has been shown to decrease nursing workload and is associated with time savings compared to manual assessments (29).

(29) See bibliography at top of page.


Staff education focusing on both the pupillometer system operation and its clinical utility is essential to success of pupillometer program adaptation. NeurOptics stands ready to support staff education needs by working with clinical educators/managers to develop a comprehensive day/night/weekend staff education plan according to institutional requirements.  Education focuses on operation of the NPi-200 Pupillometer and conceptual understanding of how pupillometry can help clinicians better manage critically ill patients. NeurOptics strongly recommends planning staff education to align closely with the date of pupillometer installation so that staff can use the devices immediately once trained.

NeurOptics will work with the critical care leadership to identify the timing and framework of clinical staff education required that will be conducted by NeurOptics personnel. NeurOptics estimates that all critical care unit staff working during the initial training period will receive one-on-one inservice education to ensure each clinician is fully trained. To reinforce the training and operation skills, supplementary training scheduled four-to-six weeks following the initial training is recommended, as well as inclusion of pupillometry training in unit Skills Days. Physicians in the critical care unit, as well as midlevel providers, will need to be trained on use of the device and interpretation of the data. NeurOptics has local representatives that can assist, as well as a network of trained Clinical Specialists.

Protocol Establishment

It is important to establish unit protocols and guidelines for use of the Pupillometer. The protocol/guideline should include baseline pupillometry readings on appropriate patients upon admission to the critical care unit along with guidelines for ongoing measurements for trending of data. Hospital approved guidelines are available from your NeurOptics’ representative for use when developing protocols/guidelines.

Critical Success Factors in Adapting Pupillometry

In order to achieve the benefits previously identified, the automated pupillometry program must have intensive collaboration of a multidisciplinary team of professionals including nurses, providers, nursing leadership, Biomedical Engineering, Information Technology, and Supply Chain Management.