Indication criteria for cochlear implants and hearing aids: impact of audiological and non-audiological findings

Abstract

Owing to technological progress and a growing body of clinical experience, indication criteria for cochlear implants (CI) are being extended to less severe hearing impairments. It is, therefore, worth reconsidering these indication criteria by introducing novel testing procedures. The diagnostic evidence collected will be evaluated. The investigation includes postlingually deafened adults seeking a CI. Prior to surgery, speech perception tests [Freiburg Speech Test and Oldenburg sentence (OLSA) test] were performed unaided and aided using the Oldenburg Master Hearing Aid (MHA) system. Linguistic skills were assessed with the visual Text Reception Threshold (TRT) test, and general state of health, socio-economic status (SES) and subjective hearing were evaluated through questionnaires. After surgery, the speech tests were repeated aided with a CI. To date, 97 complete data sets are available for evaluation. Statistical analyses showed significant correlations between postsurgical speech reception threshold (SRT) measured with the adaptive OLSA test and pre-surgical data such as the TRT test (r=-0.29), SES (r=-0.22) and (if available) aided SRT (r=0.53). The results suggest that new measures and setups such as the TRT test, SES and speech perception with the MHA provide valuable extra information regarding indication for CI.

Keywords: cochlear implant; medical audiology; psychoacoustics/hearing science; speech perception..

Figure 1

Example of the text reception threshold test: German sentence Stefan malt drei grosse Ringe, 50% masked with three different patterns. Top, random dots; middle, periodic bars; bottom, random bars.

Figure 2

Results of the text reception threshold test expressed as a boxplot. Horizontal line in the box indicates the median of the sample, the lower and upper horizontal lines represent the lower and upper quartile (25% and 75% quartiles, respectively). The whiskers indicate the last data point lying in the 1.5 times range of the interquartile range (the difference between the 25% and the 75% quartiles). The small crosses indicate outliers. (Left panel) Results of the cochlear implants (CI) candidates obtained before surgery. (Right panel) Results of the normal hearing control group. Visual masking was performed with random dots (left), periodic bars (middle) and random bars (right).

Figure 3

Comparison between performance with own hearing aid (ownHA) and Master Hearing Aid system (MHA) using the Freiburg Monosyllabic Test at 65 dB SPL, given as a histogram plot. On the abscissa, performance differences are given as percentage points; the ordinate gives the numbers of subjects who achieved these differences.

Figure 4

Results of the speech tests. (Left panel) Results of the adaptive Oldenburg sentence (OLSA) test. (Middle panel) Outcome of the fixed-level OLSA test. (Right panel) Results of the Freiburg Speech Test. All measurements were carried out before surgery using the Master Hearing Aid (MHA) and at the 6-month appointment with a cochlear implant (CI). Both OLSA test conditions (adaptive and fixed) are performed in unmodulated and modulated noise (left and right, respectively), and the Freiburg Speech Test consists of the monosyllabic test and the numbers test (left and right, respectively).

Figure 5

Results of the questionnaires. (Top left) Socio-economic status. (Top center) General state of health as assessed before surgery by the SF-12 is given as a boxplot, subdivided into physical (left) and mental (right) health. The error bars adjacent to the boxplots represent the normative values taken from Bullinger and Kirchberger. (Top right) The handicap in social settings as assessed by the Gothenburg Profile is plotted before surgery (left) and after 6-month CI use (right). (Bottom) Results of the Oldenburger Inventar estimating subjective hearing ability in quiet (bottom left), in noise (bottom, second from left), subjective localization ability (bottom, second from right) and totalled to produce an overall score (bottom right). All variables are assessed unaided (on the left of each diagram), with own hearing aid (HA, middle) and with a CI after six months of use (right).