Canine deafness is diagnosed with increasing frequency, primarily as a result of heightened awareness of the disorder. Quick, non-invasive, objective and unequivocal diagnosis of deafness, epspecially when unilateral, is achieved by means of the Brainstem Auditory Evoked Response (BAER). This is an electrodiagnostic test where the electrical activity of the brain in response to an auditory click stimulus is recorded and displayed on a computer screen.
When a sound enters the ear, tiny electrical impulses are generated by components of the auditory pathway in the inner ear and brain. Recording electrodes positioned on the head pick up these signs and they are in turn passed into a specialised electrodiagnostic machine. A series of approximately 500 stimuli, usually clicks, are passed into the ear through a headphone. In a normal hearing dog, a series of peaks and troughs is produced which is displayed on a small TV type screen. The resulting traces may be printed out and attached to a Hearing Certificate confirming the dog's hearing status.
The BAER test does not require patient co-operation and is performed without sedation in 5-7 week old puppies. They tolerate the test extremely well, often remaining asleep throughout. Older dogs may require a slight sedative to relax them and enable a good trace to be obtained, although some dogs may be tested without sedation if they are calm enough. Each ear is assessed in turn, and if the expected waveform is generated, that ear is deemed to be normal.
BAER tests are available at the Animal Health Trust, Small Animal Centre on 01638 552700, http://www.aht.org.uk/