11 Clinical Assessment of Hearing
11.1 Use of Clinical Tests
It is surprising how often a clinical assessment of hearing is omitted from the routine examination of the otology patient. Voice tests and tuning fork tests are the two main methods, but often only the Weber and Rinne tuning fork tests are performed.
Clinical tests can be used to test the following:
• Identify a hearing impairment.
• Determine the nature of a hearing loss (conductive or sensorineural).
• Grade the severity.
• Detect feigning or a non-organic hearing loss.
The main reason that clinical tests of auditory function are overlooked is that they have largely been superseded by more sensitive and reliable audio-metric tests. However, audiometry on occasions may be inaccurate or unavailable. Furthermore, exaggerated thresholds may be missed if suspicion is not aroused by clinical testing. Proponents of clinical testing suggest that audiometry may be unnecessary if the hearing is normal or the results would not influence the management.
Masking is as important in clinical testing as it is in audiometric testing. The non-test ear should always be masked when clinically testing by air conduction, and, in theory, always when performing tuning fork tests, though this is not always practicable. There are two techniques in common use.
1. The tragal rub. Occlusion of the auditory canal by putting finger pressure on the tragus with a rubbing motion is the easiest method. Using this technique, speech will be attenuated by approximately 50 dB. There is a risk of under-masking if the sound level of speech arriving at the test ear is greater than 70 dB (A) so a Bárány noise box should be used when testing an ear with a severe or profound impairment or when testing bone conduction with tuning forks.
2. The Bárány noise box. This box produces a broadband noise from a clockwork-driven source. The maximum sound output varies from approximately 90 dB (A) when a box is held at right angles to the ear and 100 dB (A) when held over the ear. These levels are sufficient to mask the non-test ear in all practical circumstances, but the main problem is cross-masking of the test ear. It should be used when a tragal rub does not provide adequate masking.