Background: The pupillary light reflex characterizes the direct and consensual response\nof the eye to the perceived brightness of a stimulus. It has been used as indicator of\nboth neurological and optic nerve pathologies. As with other eye reflexes, this reflex\nconstitutes an almost instantaneous movement and is linked to activation of the same\nmidbrain area. The latency of the pupillary light reflex is around 200 ms, although the\nliterature also indicates that the fastest eye reflexes last 20 ms. Therefore, a system with\nsufficiently high spatial and temporal resolutions is required for accurate assessment. In\nthis study, we analyzed the pupillary light reflex to determine whether any small\ndiscrepancy exists between the direct and consensual responses, and to ascertain\nwhether any other eye reflex occurs before the pupillary light reflex.\nMethods: We constructed a binocular video-oculography system two high-speed\ncameras that simultaneously focused on both eyes. This was then employed to assess\nthe direct and consensual responses of each eye using our own algorithm based on\nCircular Hough Transform to detect and track the pupil. Time parameters describing\nthe pupillary light reflex were obtained from the radius time-variation. Eight healthy\nsubjects (4 women, 4 men, aged 24ââ?¬â??45) participated in this experiment.\nResults: Our system, which has a resolution of 15 microns and 4 ms, obtained time\nparameters describing the pupillary light reflex that were similar to those reported\nin previous studies, with no significant differences between direct and consensual\nreflexes. Moreover, it revealed an incomplete reflex blink and an upward eye\nmovement at around 100 ms that may correspond to Bellââ?¬â?¢s phenomenon.\nConclusions: Direct and consensual pupillary responses do not any significant\ntemporal differences. The system and method described here could prove useful\nfor further assessment of pupillary and blink reflexes. The resolution obtained revealed\nthe existence reported here of an early incomplete blink and an upward eye movement.
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