To evaluate B-mode ultrasound as a novel method for the examination of pupillary function in healthy and pathological conditions and to provide normal values for the pupillary reflex as assessed by B-mode ultrasound.

B-mode ultrasound examination was doable in approximately 5 minutes only and was well tolerated by all participants.  In the healthy subjects, the mean ± standard deviation left and right pupillary diameters (PD) at rest were 4.7 ± 0.8 and 4.5 ± 0.8 mm. Following an ipsilateral light stimulus (L_stim), left and right constricted PD were 2.8 ± 0.6 and 2.7 ± 0.6 mm. Following a contralateral L_stim, left and right constricted PD were 2.7 ± 0.6 and 2.6 ± 0.5 mm. In pathological conditions, eyes with RAPD showed lower absolute constriction amplitude of the pupillary diameter and a longer pupillary constriction time after ipsilateral light stimulus. In eyes affected by RAPD, visual acuity correlated with the absolute constriction amplitude (r=0.75, p=0.001).

B-mode ultrasound is a simple, rapid and objective  method for the quantitative assessment of pupillary function in healthy and in pathological conditions, which may prove useful in a variety of settings where eyelid retraction is impeded or an infrared pupillometry device is unavailable. B-mode ultrasound could be applied in clinical practice to document a RAPD.