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Simple Eye Measurement Helps Improve Outcomes for Brain Injury Patients

Simple Eye Measurement Helps Improve Outcomes for Brain Injury Patients content piece image
The NPi-200 pupillometer. Credit: NeurOptics
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Pupillometry might sound like a technique a teacher would use to keep her class under control, but it’s actually an ingenious way of assessing brain health by measuring data from patients’ eyes. This process used to be a rather imprecise art, but new technology has helped standardize pupillometry, and a study from earlier this year highlighted how such measurements are now helping treat patients with life-threatening brain injuries. We spoke to Kathleen Pierson, Vice President, Global Sales and Marketing, at pupillometry leader NeurOptics, to find out more.

Ruairi Mackenzie (RM): What is a pupillometer?

Kathleen Pierson (KP): The pupillometer is a simple handheld device that provides accurate, reliable and objective pupil size and reactivity data, independent of the examiner. The pupillometer expresses pupil reactivity numerically so that now, for the first time ever, both pupil size and reactivity can be trended for changes, just like other vital signs. The pupillometer is used clinically in critical care and emergency medicine, and provides clinicians with an objective, accurate, and trendable pupil reactivity measurement, which is crucial to the neurological examination. You can liken it to thermometer technology.  Thermometer technology replaced hand-to-skin subjective temperature assessment. Digital heart rate replaced manual hand-to-pulse subjective assessment. All vital signs today in 2019, like blood pressure or heart rate, are now automated and digitalized. Automated pupillometry is a natural progression in technology that provides accurate, reliable, and objective pupil reactivity measurement expressed numerically as “NPi” (Neurological Pupil index), and pupil size.

RM: Why is pupillometry an effective diagnostic technique?

KP: Think about the eye being the window to the brain in critical care and emergency medicine. In those settings, performing a comprehensive neurological exam is a cornerstone of care for critically ill patients with a whole range of neurological injuries, including traumatic brain injury, stroke, and tumors. A comprehensive neuro exam is also crucial in the care of patients at risk of a secondary neurological injury, for example, complex CV surgery, transplant, and liver failure patients, or any patient at risk of stroke. When performing a neuro assessment, the pupils are closely examined, and the pupillary assessment becomes a window through which the medical staff evaluate the patient’s neurologic status.  Specifically, the clinical staff evaluates the functional status of the second cranial nerve (CN II) and the third cranial nerve (CN III). When performing a neuro exam, the clinician is closely examining the pupils, and the pupillary assessment becomes a window through which the clinician can assess the patient’s neurological health. 

RM: A recent study conducted at the University of Texas Southwestern Medical Centre has found that the NPi-200 could help change outcomes for patients with brain injury. How?

KP: The pupillometer is a very simple, handheld device that replaces traditional manual, subjective pupillary assessment by nurses using a penlight, which has been shown to produce poor interrater reliability.  With a penlight assessment, the human is wrong two thirds of the time when assessing non-reactive pupils, as has been established in an important published clinical study. With the pupillometer, clinicians are able to obtain accurate, reliable, objective, and trendable pupil size and reactivity measurements.

The aim of the study was to examine the role of automated pupillometry in patients following subarachnoid hemorrhage (SAH) when cerebral vasospasm, causing delayed cerebral ischemia (DCI), is a source of significant morbidity. What the study found is that NPi decreased preceding clinical neurological decline over 70% of the time in a subset of those patients.  What clinicians are very excited about is the study found the NPi-200 Pupillometer has the potential to provide enough early warning to initiate therapeutic measures before the development of irreversible neurological damage.

There has been substantial scientific research published by clinicians in Europe that is very exciting. In one example, a large prospective, multicenter, double-blinded study published in December was the first of its kind to assess the prognostic value of pupillary reactivity using NPi in the acute phase of post anoxic coma to predict an unfavorable neurologic outcome after cardiac arrest. The study involved 10 centers across 8 European countries and involved 456 subjects, all post-cardiac arrest patients who were treated with targeted temperature management. The study concluded NPi had an excellent ability to predict an unfavorable outcome from day 1 post cardiac arrest, with no false positives, and significantly higher specificity than standard manual pupillary examination. The conclusions are very exciting and speak to the potential prognostic impact of establishing NPi upon admission of a patient and then continuing to measure and trend NPi throughout the patient’s admission in order to potentially help identify any neurological decompensation before it happens so that clinicians can intervene.

Another case study, from Addenbrooke’s Hospital at the Cambridge Biomedical Campus, was literally titled, “Saved by the Pupillometer!”, and beautifully illustrates the value of having an objective, reliable tool to assess pupil reactivity and pupil size in the acute care setting.  That particular case study described a 70-year-old patient who was admitted to the emergency room (ER) after a fall and was diagnosed with subdural hematoma. The ER sent him to the operating room (OR) to have the hematoma evacuated. The OR staff evaluated the patient’s pupils subjectively with a penlight and assessed his pupils as non-reactive and, instead of proceeding with surgery, moved him to the neuro ICU. The ICU staff, however, had an NPi-200 Pupillometer, which they used to assess the patient’s pupils, and they found them to be reactive. The ICU sent the patient back to the OR, where the hematoma was evacuated, and the patient ended up being discharged with a positive outcome. The NPi-200 really helped save that patient’s life.

RM: How long has it taken to introduce a device like the NPi-200? How have clinicians adopted it?

KP: Our current NPi-200 was introduced in 2014, although a previous model was available. Certainly, medical technology can take time, but what has been significant with the NPi-200 Pupillometer is the abundance of scientific research that has been published or presented in scientific sessions over the past 18 months. Clinicians have studied the technology and validated that it is superior in accuracy, indisputably, in comparison with traditional subjective assessment. Hospitals are widely adopting the technology, which is being used in critical care units, emergency rooms and trauma centers, transplant units, and stroke units in the U.S. Another 28 countries are also currently establishing pupillometry. Clinicians are now using the pupillometer and NPi to help manage cerebral edema, to help assess patients at risk of stroke, opioid toxicity assessment, neurological decompensation, and any time they need to conduct a neurologic assessment because of the accuracy and reliability the pupillometer provides.  It is very, very exciting to see how clinicians are now utilizing the technology to manage their patients.  

Kathleen Pierson was speaking to Ruairi J Mackenzie, Science Writer for Technology Networks