Bilateral sequential cochlear implantation in the congenitally deaf child: evidence to support the concept of a 'critical age' after which the second ear is less likely to provide an adequate level of speech perception on its own.

This study attempts to answer the question of whether there is a 'critical age' after which a second contralateral cochlear implant is less likely to provide enough speech perception to be of practical use. The study was not designed to predict factors that determine successful binaural implant use, but to see if there was evidence to help determine the latest age at which the second ear can usefully be implanted, should the first side fail and become unusable.Outcome data, in the form of speech perception test results, were collected from 11 cochlear implant programmes in the UK and one centre in Australia. Forty-seven congenitally bilaterally deaf subjects who received bilateral sequential implants were recruited to the study. The study also included four subjects with congenital unilateral profound deafness who had lost all hearing in their only hearing ear and received a cochlear implant in their unilaterally congenitally deaf ear. Of those 34 subjects for whom complete sets of data were available, the majority (72%) of those receiving their second (or unilateral) implant up to the age of 13 years scored 60 per cent or above in the Bamford Kowal Bench (BKB) sentence test, or equivalent. In contrast, of those nine receiving their second or unilateral implant at the age of 15 or above, none achieved adequate levels of speech perception on formal testing: two scored 29 per cent and 30 per cent, respectively, and the rest seven per cent or less.A discriminant function analysis performed on the data suggests that it is unlikely that a second contralateral implant received after the age of 16 to 18 years will, on its own, provide adequate levels of speech perception. As more children receive sequential bilateral cochlear implants and the pool of data enlarges the situation is likely to become clearer.The results provide support for the concept of a 'critical age' for implanting the second ear in successful congenitally deaf unilateral cochlear implant users. This would argue against 'preserving' the second ear beyond a certain age, in order to use newer models of cochlear implant or for the purpose of hair cell regeneration and similar procedures in the future. The results suggest a new and more absolute reason for bilateral implantation of congenitally deaf children at an early age.

Evaluation of bilaterally implanted adult subjects with the nucleus 24 cochlear implant system.

OBJECTIVE: To evaluate the speech perception benefits of bilateral implantation for subjects who already have one implant. STUDY DESIGN: Repeated measures. PATIENTS: Thirty adult cochlear implant users who received their second implant from 1 to 7 years with a mean of 3 years after their first device. Ages ranged from 29 to 82 years with a mean of 57 years. SETTING: Tertiary referral centers across the United Kingdom. MAIN OUTCOME MEASURES: Monosyllabic consonant-nucleus-consonant words and City University of New York sentences in quiet with coincident speech and noise and with the noise spatially separated from the speech by +/-90 degrees . RESULTS: At 9 months, results showed the second ear in noise was 13.9 +/- 5.9% worse than the first ear (p < 0.001); a significant binaural advantage of 12.6 +/- 5.4% (p < 0.001) over the first ear alone for speech and noise from the front; a 21 +/- 6% (p < 0.001) binaural advantage over the first ear alone when noise was ipsilateral to the first ear; no binaural advantage when noise was contralateral to the first ear. CONCLUSIONS: There is a significant bilateral advantage of adding a second ear for this group. We were unable to predict when the second ear would be the better performing ear, and by implanting both ears, we guarantee implanting the better ear. Sequential implantation with long delays between ears has resulted in poor second ear performance for some subjects and has limited the degree of bilateral benefit that can be obtained by these users. The dual microphone does not provide equivalent benefit to bilateral implants.