Assessment of repeatability of a clinical automated pupillometer

To determine the repeatability of a clinical pupillometer in healthy participants with a 5 and 30 ⁻ minute test ⁻ retest break for both Swinging-Flashlight and Low-High Luminance approach.

Methods

20 healthy participants (mean age: 27 years ±5; 9 females) placed their heads into the device’s headrest and fixated a central spot. A Swinging-Flashlight approach evoked a pupillary light reflex, stimulating alternatingly 8 times each eye by a brief diffuse white light flash followed by a continuous measurement of constriction and dilation of the direct and consensual pupils. For the Low-High Luminance setting, continuous measurements of pupil diameters for a 5 second low luminance display followed by a 5 second high luminance white light. Pupillary light reflex parameters for each test and each eye were calculated by the device. Repeatability was investigated after a 5-minute break time and during a control experiment for 21 participants after a 30-minute break for each approach in counterbalanced order using Bland-Altman analysis.

Results

Overall, many parameters for both Swinging-Flashlight and Low-High Luminance approach showed retest biases for all pupil light reflex parameters after a 5-minute test-retest break. These biases were almost completely reduced after a 30-minute break between test and retest for both approaches. The test-retest variabilities as expressed using the Coefficient of Repeatability was reduced after 30-minutes for the majority of the Low-High Luminance results but not for results of the Swinging-Flashlight method.

Conclusions

Clinical pupillometry includes the Swinging Flashlight Test (SFL) and Low-High Luminance assays. In SFL, many pupillary dynamic metrics showed test-retest bias at a 5-minute interval, whereas relative afferent pupillary defect (RAPD) measurements remained unbiased at both 5 and 30-minute intervals. Similarly, Low-High Luminance testing showed minimal bias after 30 minutes but exhibited bias at the 5-minute interval. Thus, when evaluating multiple pupillary parameters in scientific or clinical settings, RAPD is less susceptible to bias, while other metrics require longer intervals between testing and retesting.