title: Parasympathetic Nervous System Dysfunction, as Identified by Pupil Light Reflex, and Its Possible Connection to Hearing Impairment.
abstract: BACKGROUND
  Although the pupil light reflex has been widely used as a clinical diagnostic tool for autonomic nervous system dysfunction, there is no systematic review available to summarize the evidence that the pupil light reflex is a sensitive method to detect parasympathetic dysfunction. Meanwhile, the relationship between parasympathetic functioning and hearing impairment is relatively unknown.
  
  
  OBJECTIVE
  To 1) review the evidence for the pupil light reflex being a sensitive method to evaluate parasympathetic dysfunction, 2) review the evidence relating hearing impairment and parasympathetic activity and 3) seek evidence of possible connections between hearing impairment and the pupil light reflex.
  
  
  METHODS
  Literature searches were performed in five electronic databases. All selected articles were categorized into three sections: pupil light reflex and parasympathetic dysfunction, hearing impairment and parasympathetic activity, pupil light reflex and hearing impairment.
  
  
  RESULTS
  Thirty-eight articles were included in this review. Among them, 36 articles addressed the pupil light reflex and parasympathetic dysfunction. We summarized the information in these data according to different types of parasympathetic-related diseases. Most of the studies showed a difference on at least one pupil light reflex parameter between patients and healthy controls. Two articles discussed the relationship between hearing impairment and parasympathetic activity. Both studies reported a reduced parasympathetic activity in the hearing impaired groups. The searches identified no results for pupil light reflex and hearing impairment.
  
  
  CONCLUSIONS
  As the first systematic review of the evidence, our findings suggest that the pupil light reflex is a sensitive tool to assess the presence of parasympathetic dysfunction. Maximum constriction velocity and relative constriction amplitude appear to be the most sensitive parameters. There are only two studies investigating the relationship between parasympathetic activity and hearing impairment, hence further research is needed. The pupil light reflex could be a candidate measurement tool to achieve this goal.
authors.affiliation: Section Ear & Hearing, Dept. of Otolaryngology-Head and Neck Surgery and EMGO Institute for Health and Care Research, VU University medical center, Amsterdam, The Netherlands.|Eriksholm Research Centre, Oticon A/S, Snekkersten, Denmark.
authors.forename: Yang
authors.identifier: http://orcid.org/0000-0002-4299-1282
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Section Ear & Hearing, Dept. of Otolaryngology-Head and Neck Surgery and EMGO Institute for Health and Care Research, VU University medical center, Amsterdam, The Netherlands.|Department of Behavioural Sciences and Learning, Linköping University, Linköping, Sweden.|Linnaeus Centre HEAD, The Swedish Institute for Disability Research, Linköping and Örebro Universities, Linköping, Sweden.
authors.forename: Adriana A
authors.initials: AA
authors.lastname: Zekveld
authors.affiliation: MRC/CSO Institute of Hearing Research, Scottish Section, Glasgow, United Kingdom.
authors.forename: Graham
authors.initials: G
authors.lastname: Naylor
authors.affiliation: Section Ear & Hearing, Dept. of Otolaryngology-Head and Neck Surgery and EMGO Institute for Health and Care Research, VU University medical center, Amsterdam, The Netherlands.|Eriksholm Research Centre, Oticon A/S, Snekkersten, Denmark.
authors.forename: Barbara
authors.initials: B
authors.lastname: Ohlenforst
authors.affiliation: Medical Library, VU University Amsterdam, Amsterdam, the Netherlands.
authors.forename: Elise P
authors.initials: EP
authors.lastname: Jansma
authors.affiliation: Institute of Physiology and Pathology of Hearing, Warsaw, Poland.
authors.forename: Artur
authors.initials: A
authors.lastname: Lorens
authors.affiliation: Eriksholm Research Centre, Oticon A/S, Snekkersten, Denmark.|Linnaeus Centre HEAD, The Swedish Institute for Disability Research, Linköping and Örebro Universities, Linköping, Sweden.|Department of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden.
authors.forename: Thomas
authors.initials: T
authors.lastname: Lunner
authors.affiliation: Section Ear & Hearing, Dept. of Otolaryngology-Head and Neck Surgery and EMGO Institute for Health and Care Research, VU University medical center, Amsterdam, The Netherlands.
authors.forename: Sophia E
authors.initials: SE
authors.lastname: Kramer
mesh_terms: D000328:Adult; D001342:Autonomic Nervous System Diseases / Q000150:complications / Q000175:diagnosis*; D005260:Female; D034381:Hearing Loss / Q000175:diagnosis* / Q000209:etiology; D006801:Humans; D008027:Light; D008297:Male; D008875:Middle Aged; D011680:Pupil / Q000502:physiology*; D012025:Reflex, Pupillary / Q000502:physiology*