Cochlear implants' performance not affected by amount of hearing loss in the implanted ear

Hearing-impaired individuals with severe to profound hearing loss and poor speech understanding who possess some residual hearing in one ear may experience significant communication benefit from a cochlear implant even if it is placed in the worse-hearing ear, a Johns Hopkins study suggests.

There is growing evidence that the amount of hearing in an ear prior to surgery is unrelated to a patient's ability to interpret speech using an implant, says Howard W. Francis, M.D., lead author of the study and an associate professor of otolaryngology-head and neck surgery. Therefore, the better-hearing ear could be saved for the continued use of a hearing aid or future technology to complement a cochlear implant, Francis says.

Reporting in the August issue of the journal Ear and Hearing, Francis and colleagues compared patients with no residual hearing, patients with some residual hearing in one ear and patients with some residual hearing in both ears. The patients' ability to interpret sounds and speech was measured before and after cochlear implant surgery.

Patients with residual hearing in one or both ears prior to surgery scored significantly higher on the speech perception tests following surgery, even when the implanted ear was profoundly deaf prior to surgery. The researchers also noted that patients' ability to interpret speech in a noisy environment increased dramatically over time in proportion with the amount of residual hearing in the non-implanted ear.

"In cases where even a small amount of hearing ability remains in one ear, the central nervous system is better able to integrate auditory information with a cochlear implant, and equally so from either ear," Francis says. "This speaks to the brain's circuitry and its ability to interpret electrical signals generated by the implant even in the presumably more degenerated ear."