A Figtree teenager born with no ears is challenging a funding policy that restores hearing on one side but not the other. Shannon Fox's family recently spent thousands of dollars for her second hearing implant after she was refused financial support from Australian Hearing.The agency - funded by the Department of Health and Ageing - says its decision was based on research showing an implant in a single ear produces "a good outcome". However, that view is at odds with Shannon's surgeon and she is challenging it for the sake of future patients.Her second implant was activated on Tuesday and she said it had "greatly" improved her hearing."Before, everyone was the same - same tone, same volume. I just can't put into words how it's changed - it's a new feeling, it's like a new dimension of life."The 17-year-old Figtree High School student was born without ear canals or fully formed outer ears, a type of congenital aural atresia. At age 11, she underwent surgery to fit the only implant suitable in such cases - a Bone Anchored Hearing Aid (BAHA) - to her right side.Last year, a teacher, Jennifer English, had a modern version of the device implanted after losing hearing in one side to a tumour.The pair shared their experiences and Shannon came away believing she would benefit from having a second BAHA.Her family approached Australian Hearing about funding for the $7000 device but was told research had shown a single implant "provides a good outcome".Hearing Australia's executive manager clinical practice Michele Clapham told the Mercury the agency "had no objective measure provided to us that demonstrates that this person will benefit from two [implants]. When you're wearing two aids and a sound comes to you, it will arrive at one ear at a slightly different time from the other ear. Our brain records that difference and we can identify the direction that the sound is coming from."The BAHA works in a different way and we don't have those timing differences so we don't achieve those same sorts of benefits," Ms Clapin said.The Fox family paid for the surgery themselves after seeking advice from doctors including Shannon's surgeon, St Vincent's Hospital's Dr Phillip Chang."There is irrefutable evidence that for selected patients, bilateral hearing implants far exceed the hearing results of only one," he said. "In Shannon's case, I believe that one hearing implant is indeed for a 'good outcome' but it falls far short of being the optimal outcome."Shannon has written to ministers, politicians and agencies and plans to reveal the benefits she says she is now experiencing.