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Hearing and Deafness in Dogs ( A presentation made to the New Brunswick Veterinary Medical Association, September, 2007) Aubrey A. Webb, DVM, PhD Faculty of Veterinary Medicine University of Calgary (www.vet.ucalgary.ca) And Western Veterinary Specialist Centre (www.westernvet.ca) Outline z Hearing in dogs z z Normal aural (ear) anatomy How does a dog hear? z z z z Deafness in dogs z z Deafness – What is it? Types of deafness z z z Sound Hearing Sequence of events leading to hearing Conductive vs. neurologic Congenital vs. acquired Diagnosis of Deafness z z z Signalment, history, physical and neurologic examinations Aural examination Electrodiagnostic examination Evolution of vestibulocochlear system z Thought to have evolved, in part, from the inner ear and lateral line system seen in fish (octavolateralis system) z Fish detect sounds and motion through the inner ear and lateral line system 3 Compartments of the Ear z Outer Ear z Middle Ear z Inner Ear Normal Aural Anatomy z Outer ear z The outer portion of the hearing apparatus z z beginning from the outside of the ear and ending at the level of tympanic membrane Function: to capture and focus sound into the vertical and horizontal auditory canals From Hills Atlas of Clinical Anatomy Aural Anatomy z Middle ear z An air filled cavity located in the temporal bone of the skull z Contains three tiny bones z z Malleus (hammer) z Incus (anvil) z Stapes (stirrup) Function: to conduct sound waves from the external environment to the inner ear From Hills Atlas of Clinical Anatomy Aural Anatomy From Hills Atlas of Clinical Anatomy From www.hearingaidscentral.com Normal Aural Anatomy z Inner ear z Comprised of the cochlea z Found within the petrous bone of the skull z Function: to convert mechanical energy to electrical energy that is then transmitted to the brain From Hills Atlas of Clinical Anatomy How does a dog hear? z What is sound? z Our perception of vibrations (i.e. sound waves) detected by the hearing apparatus z What is hearing? z The ability to detect sound How does a dog hear? From Hills Atlas of Clinical Anatomy How does a dog hear? From Hills Atlas of Clinical Anatomy From Kandel et al, Principles of Neural Science Organ of Corti: Contained within the cochlea Contains hair cells that convert sound waves into electrical signals that are transmitted to the brain From Kandel et al, Principles of Neural Science How does a dog hear? Sound Waves Movement of bones in middle ear Movement of hair cells in the Inner Ear Electrical Impulse from Inner Ear to Brain Outline z Hearing in dogs z z Normal aural (ear) anatomy How does a dog hear? z z z z Deafness in dogs z z Deafness – What is it? Types of deafness z z z Sound Hearing Sequence of events leading to hearing Conductive vs. neurologic Congenital vs. acquired Diagnosis of Deafness z z z Signalment, history, physical and neurologic examinations Aural examination Electrodiagnostic examination Pinna Vertical Canal Hammer, anvil, stirrup Horizontal Canal Cochlea Tympanic Membrane Middle ear cavity Deafness z The inability to hear Types of Deafness in Dogs z Conduction deafness z Deafness resulting from failure of conduction of sound waves to the inner ear z Neurologic (sensorineural) deafness z Deafness resulting from failure of generating or sending electrical impulses from the inner ear to the brain Types of Deafness in Dogs z Congenital z Born with deafness or defect leading to deafness z z z Inherited Drug toxicity Acquired z Deafness that is acquired after birth z z z z z Ear infections Neoplasia Drug toxicity Loud noise exposure Presbycusis (old-age) Congenital Sensorineural Deafness in Dogs Coppens et al, 2003 Breeds of Dogs Strain, Vet J, 2004 Prevalence in particular breeds Strain, Vet J, 2004 Differences between countries (dalmatians) Norway: 3.6% of 1843 dalmatians bilaterally deaf in Norway Greibrokk, JAAHA, 1994 UK: Wood, Lakhani, Henley; Vet J, 2004 Germany: Juraschko, Vet J, 2003 USA: Strain, Vet J, 2004 Blue eyes and deafness (dalmatians) Reference Eye colour Bilateral deafness Strain et al. Brown/brown 6.9 1992 Holliday et al. 1992 Unilateral deafness Normal Number of dogs 20.3 72.8 915 Brown/blue 18.4 30.3 51.3 76 Blue/blue 12.5 43.8 43.8 32 Brown/brown 5.6 18.8 75.5 799 Brown/blue 15.8 39.5 44.7 76 Blue/blue 22.2 33.3 44.4 27 From Cattanach, jsap, 1999 Effect of parental hearing status (dalmatians) Wood, Lakhani, Henley; Vet J, 2004 Congenital Sensorineural Deafness z Breed predisposition z z Coat colour z z z Breeds with spotting, roaning, merling, excessive white White cats (any colour iris) Iris colour z z Numerous breeds Animals with blue eyes (1 or 2) more predisposed Mode of inheritance z z Unknown Dogs with one ear deaf as likely to produce deaf puppies as dogs with deafness in both ears Breeding Advice (all predisposed breeds unless proven otherwise) z Do not breed affected animals (whether they are unilateral or bilaterally deaf) z Avoid breeding to blue-eyed animals z Test all puppies in a litter z Will give an indication of whether a particular breeding resulted in a lot of puppies with deafness Unaffected ear Otitis externa Outline z Lesson 1. Hearing in dogs z z Normal aural (ear) anatomy How does a dog hear? z z z z Lesson 2. Deafness in dogs z Types of deafness z z z Sound Hearing Sequence of events leading to hearing Congenital vs. acquired Conductive vs. neurologic Lesson 3. Diagnosis of Deafness z z z Signalment, history, physical and neurologic examinations Aural examination Electrodiagnostic examination Diagnosis of Deafness z How might you determine what form of deafness a dog has? Diagnosis of Deafness z Signalment z History z Physical and Neurologic examinations z External aural (ear) examination z Electrodiagnostic evaluation SIGNALMENT and HISTORY PHYSICAL and NEUROLOGIC EXAMINATIONS EXTERNAL AURAL EXAMINATION http://courses.vetmed.wsu.edu/ http://courses.vetmed.wsu.edu/ http://courses.vetmed.wsu.edu/ ELECTROPHYSIOLOGICAL TESTING http://www.geocities.com/Heartland/2169/baer.html Brainstem Auditory-Evoked Response (BAER) testing BAEP Click 1:1 L RIGHT LEFT 1:2 R LEFT RIGHT 1 (ms) Hearing in both ears Hearing only in right ear For more information on Canine Hearing and Deafness z Dr. George Strain’s (Louisiana State University) Website: www.lsu.edu/deafness/deaf.htm z Lesson 1. Hearing in dogs z z Normal aural (ear) anatomy How does a dog hear? z z z z Lesson 2. Deafness in dogs z Types of deafness z z z Sound Hearing Sequence of events leading to hearing Congenital vs. acquired Conductive vs. neurologic Lesson 3. Diagnosis of Deafness z z z Signalment, history, physical and neurologic examinations Aural examination Electrodiagnostic examination Questions?