title: A high-resolution binocular video-oculography system: assessment of pupillary light reflex and detection of an early incomplete blink and an upward eye movement.
abstract: BACKGROUND
  The pupillary light reflex characterizes the direct and consensual response of the eye to the perceived brightness of a stimulus. It has been used as indicator of both neurological and optic nerve pathologies. As with other eye reflexes, this reflex constitutes an almost instantaneous movement and is linked to activation of the same midbrain area. The latency of the pupillary light reflex is around 200 ms, although the literature also indicates that the fastest eye reflexes last 20 ms. Therefore, a system with sufficiently high spatial and temporal resolutions is required for accurate assessment. In this study, we analyzed the pupillary light reflex to determine whether any small discrepancy exists between the direct and consensual responses, and to ascertain whether any other eye reflex occurs before the pupillary light reflex.
  
  
  METHODS
  We constructed a binocular video-oculography system two high-speed cameras that simultaneously focused on both eyes. This was then employed to assess the direct and consensual responses of each eye using our own algorithm based on Circular Hough Transform to detect and track the pupil. Time parameters describing the pupillary light reflex were obtained from the radius time-variation. Eight healthy subjects (4 women, 4 men, aged 24-45) participated in this experiment.
  
  
  RESULTS
  Our system, which has a resolution of 15 microns and 4 ms, obtained time parameters describing the pupillary light reflex that were similar to those reported in previous studies, with no significant differences between direct and consensual reflexes. Moreover, it revealed an incomplete reflex blink and an upward eye movement at around 100 ms that may correspond to Bell's phenomenon.
  
  
  CONCLUSIONS
  Direct and consensual pupillary responses do not any significant temporal differences. The system and method described here could prove useful for further assessment of pupillary and blink reflexes. The resolution obtained revealed the existence reported here of an early incomplete blink and an upward eye movement.
authors.affiliation: Institute of Physics Applied to the Sciences and Technologies, University of Alicante, Alicante, Spain. julian.espinosa@ua.es.|Department of Optics, Pharmacology and Anatomy, University of Alicante, Alicante, Spain. julian.espinosa@ua.es.
authors.forename: Julián
authors.initials: J
authors.lastname: Espinosa
authors.affiliation: Department of Optics, Pharmacology and Anatomy, University of Alicante, Alicante, Spain. anabelen.roig@ua.es.
authors.forename: Ana Belén
authors.initials: AB
authors.lastname: Roig
authors.affiliation: Institute of Physics Applied to the Sciences and Technologies, University of Alicante, Alicante, Spain. jorge.perez@ua.es.|Department of Optics, Pharmacology and Anatomy, University of Alicante, Alicante, Spain. jorge.perez@ua.es.
authors.forename: Jorge
authors.initials: J
authors.lastname: Pérez
authors.affiliation: Institute of Physics Applied to the Sciences and Technologies, University of Alicante, Alicante, Spain. david.mas@ua.es.|Department of Optics, Pharmacology and Anatomy, University of Alicante, Alicante, Spain. david.mas@ua.es.
authors.forename: David
authors.initials: D
authors.lastname: Mas
mesh_terms: D000328:Adult; D000886:Anthropometry / Q000295:instrumentation* / Q000379:methods; D001767:Blinking / Q000502:physiology*; D003941:Diagnostic Techniques, Ophthalmological / Q000295:instrumentation*; D004867:Equipment Design; D005133:Eye Movements / Q000502:physiology*; D005137:Eye, Artificial; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008297:Male; D008875:Middle Aged; D010775:Photic Stimulation; D011680:Pupil / Q000502:physiology; D011930:Reaction Time; D012016:Reference Values; D012025:Reflex, Pupillary / Q000502:physiology*; D012438:Saccades / Q000502:physiology; D014741:Video Recording / Q000295:instrumentation* / Q000379:methods; D055815:Young Adult