18Which ear, one or both

TThe configuration decision

Candidacy decides whether; ear selection decides where and how many. The choice draws on each ear's aided scores and history, the patient's residual hearing, and the goals of localisation and hearing in noise. It is the bridge from the candidacy decision to the surgical plan.

CPoorer ear or better ear?

The instinct to implant the better ear has largely given way. Studies show that results from implanting the poorerear are statistically equivalent to implanting the better one, so implanting the poorer ear is usually favoured — it addresses the worse ear and preserves the better ear for acoustic hearing (a bimodal aid) or for future use. Important exceptions remain: a congenitally deaf ear in an older adult, or a malformed or long-dead ear, may respond so poorly that the better ear is the wiser choice.[2003]

COne ear or both

Two ears are better than one for localisation and speech in noise, which depend on comparing the inputs to both sides (Chapter 3). Bilateral implantation — done simultaneously or sequentially — restores that binaural advantage, and is now common, especially in children, where implanting both ears within the sensitive period avoids an aural preference developing for one side.

CBimodal — implant plus aid

When the non-implanted ear has usable hearing, keeping a hearing aid on it gives a bimodal combination: the implant supplies the high-frequency and spectral detail, the aid adds low-frequency acoustic information the implant conveys poorly. Many recipients report fuller, more natural sound bimodally, and the low-frequency cues can help with pitch and in noise. Which ear, one or two, and bimodal or not — the answer is individual, and flows from the candidacy assessment into the operation itself.

TCBalance, and testing the ear on its own

Hearing is not the only axis. Implantation puts balance at risk in the operated ear (around a 38% chance of some vestibular loss, ~10% severe), and post-operative vertigo is more likely in an ear that still has a recordable caloric response. So when the hearing odds are close, the tie-breaker is to implant the weaker-balancing ear and spare the better balancer — and never to sacrifice an only-balancing ear (Module 11). Ear choice is a hearing and a balance decision.

One methodological caution ties back to the criteria: a binaural best-aided score can mask a poorer ear that genuinely qualifies, so the ear to be implanted should be tested on its own. Where imaging shows cochlear asymmetry or there is doubt the ear will respond at all, transtympanic/promontory stimulation can help choose. And patients are counselled that delayed-onset dizziness occurs in a substantial minority after surgery, occasionally persisting — a point that belongs in the ear-selection conversation.