This has been a subject that I have had strong views on. However, overtime I have changed my position slightly. But I have taken some research from several recent journals including https://www.ihsinfo.org/ihsv2/Ceus/pdf/2008_July_Aug_Sept_THP.pdf to help clarify my current stance.
Hearing aid fitting software has a built- in audiometer to obtain hearing levels with the hearing aid in the ear. This procedure is called in situ audiometry. “In situ” is a Latin phrase meaning “in place” . In the case of hearing instruments, it refers to measurements taken with the hearing aid in its natural location: correctly fitted in the ear. The procedure also accounts for the effects of the depth of the instrument in the ear canal, the effectiveness of the seal in the ear canal, the effects of venting, and the specific receiver in that instrument. When we are using the fitting software to set the target and perform the initial adjustments we rely exclusively on the hearing levels (HTLs) obtained during the audiologic evaluation. The fitting formulas used to set the target gain contain the proper algorithms to compute the gain targets based on the desired input levels and hearing instrument style. However, these algorithms are all based on average data. By including data obtained for your specific patient and his or her specific hearing instrument, we are adding a level of customization that patients expect from the sophisticated digital technology used today.
Once the HTLs are corrected for the hearing aid insertion effects, the hearing aid must be calibrated so that its gain response matches the gain targets. Real-ear measurements as a technique for objectively verifying the performance characteristics of a hearing aid are recommended as a best practice in hearing aid fittings (Valente, 2006). However, it is not widely used for reasons such as expense, time limitations, and the need for cumbersome equipment. As a result, about 60% of hearing professionals do not use real-ear measurements (Kirkwood, 2006). Differences in the acoustic characteristics of the ear canals are quite apparent and speak to the need for individual measures to add precision to the fitting rather than relying on average data. The target match will be inaccurate for the individual ear to the extent that the average RECD is different for the ear under test.
It is essential when achieving fitting success that the hearing aid prescription is verified. Without verification you do not know how the hearing aid is performing and therefore whether the patient is benefiting. I would estimate that at least 75% of private hearing centres still DO NOT verify their fittings, in comparison to 95% of NHS departments that DO verify their fittings. What this means is that ‘potentially’ most premium and advanced hearing aids fitted privately, ‘maybe’ under performing in comparison to more basic hearing aids fitted by the NHS. National hearing aid companies do not verify their fittings generally and often fit the aid to the manufacturers settings. When adjustments are made they are often made blindly without knowing the effect they have on output. The research indicates that verification is still needed to ensure (https://www.ncbi.nlm.nih.gov/pubmed/21376007) prescription is met and that in situ measures are not enough on their own, a stand alone verification device provides the best option. I used to feel that in situ measurements, would sufficiently tailor hearing aid gain to accommodate different ear canal properties. I naively used to make that assumption based on the patients first fit satisfaction and acceptance, as patients who were fitted to REM targets were often less satisfied than patients who were fitted using in situ. After reviewing many of my fittings using real ear measurements I have found that some manufacturers match to target better than others, but that there is still room for improvement in 7 out of 10 patients. Using data obtained directly from your patient will ensure the most accurate initial fitting and will help deliver high patient satisfaction. Therefore, I feel that a combination of both will result in a more precise fitting that is more representative of the individual rather than average data. If a centre is doing neither then you should really consider whether you should use them.
If you feel that your hearing aid is not performing properly or that it is not programmed correctly, then contact us on 01494 765144.