Quantitative pupillometry, a new technology: normative data and preliminary observations in patients with acute head injury

Technical note

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✓ The authors prospectively used a new hand-held point-and-shoot pupillometer to assess pupillary function quantitatively. Repetitive measurements were initially made in more than 300 healthy volunteers ranging in age from 1 to 87 years, providing a total of 2432 paired (alternative right eye, left eye) measurements under varying light conditions. The authors studied 17 patients undergoing a variety of nonintracranial, nonophthalmological, endoscopic, or surgical procedures and 20 seniors in a cardiology clinic to learn more about the effects of a variety of drugs. Additionally, the authors carried out detailed studies in 26 adults with acute severe head injury in whom intracranial pressure (ICP) was continuously monitored. Finally, five patients suffering from subarachnoid hemorrhage were also studied.

Quantitative pupillary measurements could be reliably replicated in the study participants. In healthy volunteers the resting pupillary aperture averaged 4.1 mm and the minimal aperture after stimulation was 2.7 mm, resulting in a 34% change in pupil size. Constriction velocity averaged 1.48 ± 0.33 mm/second. Pupillary symmetry was striking in both healthy volunteers and patients without intracranial or uncorrected visual acuity disorders. In the 2432 paired measurements in healthy volunteers, constriction velocity was noted to fall below 0.85 mm/second on only 33 occasions and below 0.6 mm/second on eight occasions (< one in 310 observations).

In outpatients, the reduction in constriction velocity was observed when either oral or intravenous narcotic agents and diazepam analogs were administered. These effects were transient and always symmetrical.

Among the 26 patients with head injuries, eight were found to have elevations of ICP above 20 mm Hg and pupillary dynamics in each of these patients remained normal. In 13 patients with a midline shift greater than 3 mm, elevations of ICP above 20 mm Hg, when present for 15 minutes, were frequently associated with a reduction in constriction velocity on the side of the mass effect to below 0.6 mm/second (51% of 156 paired observations). In five patients with diffuse brain swelling but no midline shift, a reduction in constriction velocities did not generally occur until the ICP exceeded 30 mm Hg. Changes in the percentage of reduction from the resting state following stimulation were always greater than 10%, even in patients receiving large doses of morphine and propofol in whom the ICP was lower than 20 mm Hg. Asymmetry of pupillary size greater than 0.5 mm was observed infrequently (< 1%) in healthy volunteers and was rarely seen in head-injured patients unless the ICP exceeded 20 mm Hg. Pupillometry is a reliable technology capable of providing repetitive data on quantitative pupillary function in states of health and disease.

Article Information

Address reprint requests to: Lawrence F. Marshall, M.D., University of California at San Diego, Neurosurgical Research, 4130 La Jolla Village Drive, No. 200, La Jolla, California 92037. email: lfmarshall@ucsd.edu.

© AANS, except where prohibited by US copyright law.

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Figures

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    Photograph showing the ForSite device. The color LCD displays a readout of measurement results including patient IDN, maximum aperture (maxA), minimum aperture (minA), percentage of reduction in parentheses, ambient light level indicator, pupil trajectory, stimulus profile, latency (lat), constriction velocity (C.vel.), dilation velocity (D.vel.), ICP, date, and time. The patient's IDN and ICP are manually entered by the clinician. Date and time are automatically stamped by the device.

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    Graph plotting the initial diameter of the pupil against the constriction velocity. The speed of the velocity is directly related to the initial size of the pupil. n = number of pupils.

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    Graph plotting the initial diameter of the pupil against the poststimulus diameter of the pupil. There is a constant and direct relationship between the initial diameter and the poststimulus diameter of the pupil in healthy volunteers. n = number of pupils.

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    Case 1. Quantitative changes in pupil size (right [R] eye) during a period of approximately 1.5 hours in a 21-year-old man who suffered a head injury while riding his bicycle. This patient presented with right subdural hematoma, a 4- to 5-mm midline shift to the left side, and a right occipital contusion. Specifically shown are how constriction velocity changes often precede or are concurrent with fluctuations in ICP. The percentage of reduction in the size of the pupil falls with a decrease in constriction velocity, and latency changes are seen, but rather late. Also shown are how pupillary dynamics change in response to administration of mannitol and to ventricular drainage. Note that the printout of the ForSite device shows values of constriction velocity in negative numbers.

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    Case 2. Quantitative changes in pupil size (right eye) during a period of approximately 40 minutes in a 52-year-old man who suffered a head injury sustained in a backward fall. This patient presented with a skull fracture, diffuse edema, left frontal contusion, bilateral subdural hematoma, midline shift to the right side, and brainstem hemorrhage. Specifically shown are how changes in constriction velocity frequently precede fluctuations in ICP and how the percentage of reduction in pupil size falls with a decrease in constriction velocity. Also shown are how pupillary dynamics change in response to mannitol and hyperventilation therapy. Note that the printout of the ForSite device shows values of constriction velocity in negative numbers.

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