Can real-ear measurements help to determine which patients are candidates for open fit hearing aids?
Yes, real-ear measurements can be quite useful for determining candidacy for open fit hearing aids. The patient who is an appropriate open-fit candidate needs little to no gain at or below 1000 Hz. If you're not sure, there is a quick way to find out. It only requires the patient’s audiogram, a target rule, and a real-ear unaided response (REUR) measurement. Here are the general steps you would follow, illustrated using Audioscan verification systems:
- Select Speechmap® from the on-ear test selection menu
- Enter the audiogram into your verification system
- Select a fitting formula target (such as NAL-NL2)
- Place only the probe tube in the patient’s ear(s) using typical manufacturer guidelines
- Run and record the real ear unaided response (REUR) for 65 dB speech
- Compare the displayed long term average speech spectrum (LTASS) to the displayed target
Let’s look at a few examples.
Example 1: Open Fit Candidacy
In the first example of a candidacy procedure, we’ve entered the HL audiogram shown in Figure 1.
Figure 1. Patient’s audiogram used for open fit candidacy procedure.
The HL audiogram yields the SPL audiogram (red line) with NAL-NL2 targets (pink dots) shown in Figure 2. With just the probe tube in the patient's ear canal, we ran and recorded the REUR for 65 dB speech, which is shown as the pink shaded area. The LTASS is the thick pink line in the middle of the pink shaded area. Where the LTASS is on the NAL-NL2 target dots, no gain is required. The unaided condition is already resulting in adequate SPL at those frequencies based on the NAL-NL2 targets. Since the LTASS is on target through 1000 Hz in this unaided measurement, this is an ideal candidate for an open fitting.
Figure 2. Determining open fit candidacy. In this case, no gain is needed through 1000 Hz to achieve targets, so this patient would be an ideal candidate for an open fitting.
Example 2: Open Fit Candidacy
In this second example, the patient has an audiogram with mild to moderate hearing loss in the low and mid frequencies (Figure 3).
Figure 3. Audiogram for Example 2.
This HL audiogram produced the SPL audiogram shown on the Speechmap screen in Figure 4. NAL-NL2 was also used in this example. After obtaining the REUR for 65 dB speech, and comparing its LTASS to the NAL-NL2 target values, we can clearly see that there is gain needed in the lower frequencies for the LTASS (thick pink line) to reach the NAL-NL2 targets (pink dots). In fact, there is gain needed in the mid frequencies and higher frequencies as well to achieve targets. So, this result indicates that this patient is not an ideal open fit candidate.
Figure 4. Determining open fit candidacy. In this case, gain is required in the low, mid and high frequencies to achieve targets, so this patient would not be an ideal candidate for an open fitting.
This candidacy procedure is something that could be done as part of the initial diagnostic visit, and could be used to verify whether or not your choice of an open fitting is appropriate for the patient. You can do this evaluation prior to ordering hearing instruments or selecting the coupling type, and prior to counseling the patient about hearing aid selection.
For more information on verifying open fittings, view the Audioscan CEU course, On Ear Verification of Open Fittings. For more resources from Audioscan, visit the Audioscan Expo Page on AudiologyOnline.