Neurological pupil index
Clinicians routinely check the pupils of critically injured and ill patients to monitor neurological status. However, manual pupil measurements have been shown to be subjective, inaccurate, and not repeatable or consistent. Automated assessment of the pupillary light reflex has emerged as an objective means of measuring pupillary reactivity across a range of neurological diseases, including stroke, traumatic brain injury and edema, tumoral herniation syndromes, and sports or war injuries. Automated pupillometers are used to assess an array of objective pupillary variables including size, constriction velocity, latency, and dilation velocity, which are normalized and standardized to compute an indexed score such as the Neurological Pupil index or Reflex Score.
Pupillary evaluation
Pupillary evaluation involves the assessment of two components—pupil size and reactivity to light.- Pupil size is traditionally measured using a pupil gauge to estimate the diameter in millimeters of the pupil at rest before any light is shone into the eye—pupils should be of similar size. Manual measurement is subjective and prone to error.
- Pupil light reactivity is evaluated by shining a light into a patient's eye to make the pupil constrict in reaction to the light. The pupil should dilate again when the light is moved away. The pupil's reaction is numerically graded, typically on scales from one to three, to translate how brisk the pupillary reflex is. These terms are subjective and applied without a standard clinical protocol or definition.
Scoring Indices - Neurological Pupil index (NPi) & Reflex Score
The Neurological Pupil index, or NPi, is an algorithm developed by NeurOptics, Inc. The algorithm uses an undisclosed calculation method to render the composite score. A patient's pupil measurement is obtained using a pupillometer, and the measurement is compared against a normative model of pupil reaction to light and automatically graded by the NPi on a scale of 0 to 5. However, the normative model's accuracy has not been publicly disclosed. , the world's first patented and commercially available mobile pupillometer on iOS, also produces a quantitative score called Reflex Score whose is disclosed in detail and compared directly to the patient's predetermined baseline which is also represented on a scale from 0 to 5.The numeric scale of the NPi and Reflex Score allows for a more rigorous interpretation and classification of the pupil response than manual assessment.
Interpreting Scoring
Each scoring index measurement taken is rated on a scale ranging from 0 to 5. A score equal to or above 3 means that the pupil measurement falls within the boundaries of normal pupil behavior as defined by the NPi and Reflex Score models. However, a value closer to 5 is more like the normal data or baseline test than a value closer to 3. An NPi score below 3 means the reflex is abnormal, i.e., weaker than a normal pupil response, and values closer to 0 are more abnormal than values closer to 3.Validity of Score Indices in Pupillometry
More than 45 studies published in peer-reviewed academic journals indicate the effectiveness of automated pupillometry and for use in critical care medicine, neurology, neurosurgery, emergency medicine, and applied research settings.- A study published in Vision Development & Rehabilitation demonstrates the effectiveness of automated pupillometry using Reflex, an iOS based pupillometer that does not require capital equipment.
- A study published in Neurocritical Care found that automated pupillometry is more reliable than standard clinical assessments in detecting and tracking subtle changes in cerebral edema and pupillary reactivity during osmotic therapy.
- Another study in Neurocritical Care found that abnormal NPi and pupillary light reflex measurements by pupillometer are predictive of poor outcomes very early after resuscitation from cardiac arrest, and are not usually associated with dilated pupils.
- Critical Care published a study examining the relationship between the NPi and invasive intracranial pressure in 54 patients with severe traumatic brain injury. The study found that episodes of sustained elevated ICP were associated with a concomitant decrease in NPi in subjects with intracranial hypertension.
- Data published in the Journal of Stroke and Cerebrovascular Diseases demonstrated that in patients with ischemic and hemorrhagic strokes, there is a significant correlation between the suptum pellucidum and the NPi, but not with pupil size. The authors concluded NPi assessment by automated pupillometry could be considered a useful surrogate to non-invasively monitor midline shift in stroke patients, and help in the utilization of imaging and assessing the need for intervention.
- A study published in the Journal of Neurosurgery found that the NPi may signal an early warning of potential delayed cerebral ischemia and enable preemptive escalation of care.
- A case report published in Brain Injury presented a patient who was "saved" by the use of NPi as part of his clinical assessment. Based on manual light assessment of the pupils, it was determined that the patient had suffered irreversible demise from an acute traumatic subdural hematoma. However, a subsequent assessment using an automated pupillometer with NPi showed that his pupils were in fact reactive—he then made a good recovery following treatment.
- Intensive Care Medicine published a study that found quantitative NPi had excellent ability to predict an unfavorable outcome from day one after cardiac arrest, with no false positives, and significantly higher specificity than standard manual pupillary examination.
- Four studies published in the Journal of Neuroscience Nursing concluded that automated pupillometry, using the NPi, enhanced clinical decision-making and added value to patient care in neuroscience/neurotrauma intensive care settings. One study showed that the integration of routine pupillometer assessments improves the accuracy of examinations and correlates with intracranial pressure values. Another study concluded that automated pupillometry represents an alternative to manual pupillary assessment, which may have greater interrater agreement and reliability.
- The American Journal of Critical Care revealed that critical care and neurosurgical nurses consistently underestimated pupil size, were unable to identify anisocoria, and incorrectly assessed pupil reactivity. The study concluded that automated pupillometry is a necessary tool for accuracy and consistency, and may facilitate earlier detection of subtle pupil changes, allowing for more effective and timely diagnostic and treatment interventions.