The main indication for cochlear implantation is severe-to-profound hearing loss that is not adequately treated with standard hearing aids. The clinical conditions that lead to such an indication include various scenarios, as follows:
Congenital hearing loss and prelingual deafness
Acquired hearing loss and postlingual deafness
Severe hearing loss that can be aided and that deteriorates to profound loss in childhood,adolescence, or adulthood (perilingual) and coexists with various degrees of language development
Generally, the candidacy for implantation is considered separately for adults and children. As outlined in the 1995 National Institutes of Health (NIH) consensus statement on cochlear implantation, adult candidacy is noted as being successful in postlingually deaf adults with severe-to-profound hearing loss with no speech perception benefit from hearing aids.5 In addition, the statement notes that "most marginally successful hearing aid users implanted with a cochlear implant will have improved speech perception performance." Medicare guidelines as of January 2005 allow for cochlear implantation in patients with 50% aided sentence discrimination scores and allow for 60% sentence scores in clinical trials. Clearly, the trend over time is that relaxed guidelines are better, and better cochlear implant performance and outcome have been demonstrated.
Prelingually deafened adults, although potentially suitable for cochlear implantation, must be counseled in regard to realistic expectations, as language and open-set speech discrimination outcomes are less predictable. A strong desire for oral communication is paramount for this group of patients
Children are considered candidates for cochlear implantation at age 12 months, and, because of meningitis-related deafness with progressive cochlear ossification, occasional earlier implantation is necessary. Investigations are ongoing into extending the age of early routine implantation to younger than 12 months. Audiologic criteria include severe-to-profound sensorineural hearing loss bilaterally and poor speech perception under best-aided conditions, with a failure to progress with hearing aids and an educational environment that stresses oral communication. The use of objective testing in this age group includes auditory brainstem response (ABR) testing and otoacoustic emission (OAE) testing in addition to trials of various auditory training programs, which are essential before cochlear implantation.