Her hearing implant was preapproved. Nonetheless, she got $139,000 bills for months.

Caitlyn Mai woke up one morning in middle school so dizzy she couldn't stand and deaf in one ear, the result of an infection that affected one of her cranial nerves. Though her balance recovered, the hearing never came back.

Growing up, she learned to cope — but it wasn't easy. With only one functioning ear, she couldn't tell where sounds were coming from. She couldn't follow along with groups of people in conversation — at social gatherings or at work — so she learned to lip-read.

For many years, insurers wouldn't approve cochlear implants for single-sided deafness due to concerns that it would be hard to train the brain to manage signals from a biological ear and one that hears with the aid of an implant. But research on the detrimental effects of single-sided deafness and improvements in technique changed all that.