11Widening the indications
The early cochlear implant was a last resort for adults with total, profound deafness — the only people for whom the risk of an unproven device seemed justified. As it proved safe and effective, the question changed from whether to implant to whom to implant, and the answer kept widening. Decade by decade the audiometric bar fell, the age of implantation dropped toward infancy, second ears were added, and entirely new groups — people with useful low-frequency hearing, people deaf in only one ear — were brought in. This module traces that expansion, which is still continuing, and the developmental and binaural logic that drives it.
FFrom whether to for-whom
Acceptance (Module 10) changed the central question. Once the implant was a proven, approved therapy, clinicians no longer asked whether it worked but where its boundaries lay. Almost every boundary that was drawn conservatively at first — the degree of deafness, the age, the number of ears — was later pushed outward as evidence accumulated that more people benefited than the original criteria allowed.
FTThe axes of expansion
The widening happened along several axes at once. The audiometric criterion loosened: where once only total deafness qualified, candidacy moved toward severe and even moderate loss, and — importantly — useful residual hearing stopped being a disqualifier and became something to preserve. Alongside this came the changes in age, in the number of ears, and in the opening of new clinical categories.
CLowering the age
The most scientifically grounded expansion was downward in age. After paediatric approval in 1990, the recommended age of implantation fell steadily — to one year and, in selected cases, below — driven by the evidence on the sensitive period: the earlier organised sound reaches the developing brain, the better the eventual language outcome (Chapter 3). Early implantation is the clearest example of the history being shaped by the science of plasticity.
CFrom one ear to two
Early implantation was unilateral — one ear, partly from caution and cost, partly from the assumption that one was enough. Bilateral implantation later became common as evidence showed two ears restore aspects of binaural hearing — sound localisation and hearing in noise — and as the developmental case for stimulating both auditory pathways during their sensitive period became clear (Chapter 3).
CNew categories — EAS and SSD
Two newer groups show how far the boundaries have moved. In electric-acoustic stimulation (EAS / hybrid), a person with good low-frequency hearing but a steeply sloping high-frequency loss receives a shorter electrode that adds electric high-frequency hearing while a hearing aid preserves their natural low-frequency hearing in the same ear — unthinkable when any residual hearing barred implantation. In single-sided deafness (SSD), an implant is placed in one deaf ear of a person who hears normally in the other, to restore binaural function and suppress tinnitus.
CExpansion and its limits
Expansion is not limitless or automatic. Each widening has to be justified by evidence that benefit outweighs risk for the new group, and preserving residual hearing imposes real surgical demands (atraumatic, hearing- preservation technique). But the direction of travel across the implant's history is unmistakable: from a narrow last resort toward a broad therapy for hearing loss, reaching ever more of the population the epidemiology describes (Chapter 5).
Widening who can be implanted raises a second question — can the device actually reach them? That turns the story from the original Western and Australian makers to a new, global generation of manufacturers built around cost and access: the implant goes global (Module 12).
Which modern expansion of indications applies?
Which best describes how cochlear-implant candidacy changed over time?
For a patient with good low-frequency hearing but a steep high-frequency loss, which expansion applies?