Lance has had around a 75% loss of hearing since birth, but now has (bilateral?) cochlear implants. In one article he described his implants as helping him hear most sounds, but when sounds are coming from behind him, sometimes he misses it. The result, he said, was that he'd been "wiped out" on several screens while playing basketball. Anyone who's played knows what that's like!
I'm not clear on whether Lance has one implant or two. I'll try to keep an eye out for him during the next few Cavs games, but if anyone knows for certain, please let me know.