Purpose 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.

The authors have declared no competing interest.

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