According to "Adams and Victor's Principles of Neurology," there are several types of deafness. Central deafness occurs because of damage to specific areas in the brain associated with processing auditory information. Peripheral deafness is broken down into two main categories: conductive and sensorineural. Each of these types of hearing loss occurs for different reasons. Tuning forks are used to conduct several types of tests to distinguish between conductive and sensorineural deafness.
Conductive and Sensorineural Hearing Loss
"Adams and Victor's Principles of Neurology" states that conductive hearing loss occurs when sound cannot be conducted properly into the cochlea. The cochlea is a small, spiral-shaped structure within the inner ear; this is where sound is converted into nerve impulses which travel to the brain and get perceived as the sense of "hearing." An example of conductive deafness includes hearing loss caused by an ear infection--in this case, the inner ear may be filled with fluid and make it difficult for sound to be transmitted to the cochlea; another example is a simple obstruction of the ear canal with, for instance, too much ear wax. In such a case, the wax itself prevents the sound from traveling to the cochlea. The sound cannot be conducted, and so conductive hearing loss is the result. In sensorineural deafness--sometimes called "nerve deafness"--one of two problems is responsible: either the cochlea itself is diseased, or the nerve associated with hearing--the eighth cranial nerve--is diseased. In such cases, the sound waves can make their way to the cochlea, but cannot be transmitted to the brain, and so the person has hearing loss.
Tuning Forks
Diagnosing sensorineural and conductive hearing loss is most simply done using a tuning fork that, depending on its frequency, vibrates a certain number of times per second. For example, a 512 Hertz tuning fork, when struck, will vibrate 512 times per second. Using this basic tool, a physician can distinguish between the two types of hearing loss. Different forks are made to resonate--or vibrate--at different frequencies. Some common frequencies of tuning forks include 256, 512, 1,024 and 2,048 Hertz.
Preferred Tuning Fork
In a 1988 study published in the journal "Archives of Otolaryngology--Head and Neck Surgery," the authors tested several different types of tuning forks and found that the 256 Hertz fork was the best at picking up conductive hearing loss. However, when this fork was used, many patients were falsely told that they had conductive hearing loss. This is called a false positive result and can result in unnecessary distress to the patients as well as potential costs of trying to treat a problem--in this case, hearing loss--that does not really exist. Because of the high number of false positive results, the authors concluded that the "gold standard" of tuning forks should be the 512 Hertz fork. This tuning fork does a good job of distinguishing between conductive and sensorineural deafness, but has fewer false positive diagnoses than the 256 Hertz tuning fork. The authors' conclusion is widely shared within the medical community, and the 512 Hertz fork is the most widely used fork to test for hearing loss.
References
- "Archives of Otolaryngology--Head and Neck Surgery;" The Rinne test for conductive deafness: A critical reappraisal; R.A. Chole and G.B. Cook; April 1988
- University of California, San Diego, Medical School: Rinne Test
- "Adams and Victor's Principles of Neurology"; Allan H. Ropper and Martin A. Samuels; 2009
