A: Single-sided deafness (often called SSD) happens when one ear hears normally or close to normal, but the other ear has very little or no usable hearing. This can make it difficult to tell where sounds are coming from or to hear someone speaking, especially in noisy places like restaurants.
We naturally use both ears to make sense of which direction sounds are coming from. When we have hearing in only one ear, a “head shadow effect”1 occurs, meaning the head blocks certain speech sounds from reaching the better ear.
SSD can be caused by a variety of factors, such as sudden changes in hearing health, viral infections, head trauma, or even a condition affecting the auditory nerve2. When the hearing in one ear changes, the brain no longer receives sound equally from both sides, creating an imbalance that can influence everyday communication, safety, and quality of life.
The CROS system may reduce the impact of this by giving you access to sound from both sides, making communication feel easier and more balanced.
A: The difference depends on your better-hearing ear.
CROS hearing aids are used when one ear hears well, and the other has no hearing.
BiCROS hearing aids are used when there is no hearing in one ear and some hearing loss in the other. A BiCROS system combines sound from the deaf side with amplification for the other ear.
1 Otology & Neurotology: A comparison
between wireless CROS and bone-anchored hearing devices for single-sided
deafness: a pilot study (June 2015):
https://pubmed.ncbi.nlm.nih.gov/25853611/
2 Acta Oto-Laryngologica: Etiology of single-sided deafness and asymmetrical
hearing loss (April 2017): https://pubmed.ncbi.nlm.nih.gov/28366032/
3 European Archives of Oto-Rhino-Laryngology: Clinical effectiveness of
wireless CROS (contralateral routing of offside signals) hearing aids
(September 2015): https://link.springer.com/article/10.1007/s00405-014-3133-0
4 Journal of Neurological Surgery Part B Skull Base: Nonsurgical Management of
Single-Sided Deafness: Contralateral Routing of Signal (April 2019):
https://pmc.ncbi.nlm.nih.gov/articles/PMC6438788/