Are you considering a CROS or a BiCROS hearing aids? These systems are specifically designed for people who do not have any usable hearing on one side. This condition is known as single-sided deafness and may occur with completely normal hearing in the other ear, or some lesser degree of hearing loss in the other ear. This article will explain how CROS and BiCROS systems work, who is a candidate, factors to consider with these systems, pros and cons, as well as alternative options if you are experiencing single-sided deafness. 

What Is Single-sided Deafness?

Single-sided deafness can be caused by certain viral infections, head trauma, congenital anatomical abnormalities, or the presence of a benign tumor on the hearing nerve known as acoustic neuroma. During a diagnostic hearing test, the audiologist or hearing aid dispenser will test your thresholds in a soundproof booth. The softest level at which you can detect sound in each ear is known as your threshold, and these can be categorized in degrees of hearing loss.

The second part of the audiological evaluation is to determine your understanding of words. Words are delivered to each ear individually at a comfortable volume based on your degree of hearing loss, if any, to measure your ability to discriminate and comprehend with amplification. If you have one ear in which your thresholds are in the severe to profound hearing loss range and you have very poor discrimination ability in that ear, you could be a candidate for a CROS or BiCROS. Sometimes this ear is referred to as a “dead ear” meaning that it cannot benefit from traditional hearing aids.

What is CROS?

The acronym “CROS” stands for “contralateral routing of signal” meaning that sound is picked up on one side of the head and wirelessly transmitted to the other side. A microphone is worn on the ear without usable hearing to pick up sound, and it is delivered to the transmitter worn on the ear with normal or near-normal hearing. These devices are a slim receiver-in-the-ear style to keep the ears relatively open. The normal-hearing ear should be able to pick up sound normally from that side, in addition to receiving sound from the contralateral microphone.

One of the easiest situations to envision use of a CROS device is the car. Imagine you have lost all hearing in your right ear. If you are the driver, it would be quite difficult to hear your passenger. With a CROS system, the microphone on your right ear would pick up your passenger’s voice and send it to your left ear so that you could carry on a conversation in the car. For the most part, people can carry on a very normal life with hearing in just one ear. But in these types of situations, a CROS is particularly helpful.

The same would apply when dining in a group, walking side by side, or any scenario where a desired sound source is on the side of the poorer ear. Certainly, you could be the passenger in the car or ask your walking mate to switch sides, but not all situations are so easy to accommodate. One patient of mine was hoping to teach his teenager to drive, so it was very important for him to be able to be the driver or the passenger in the car. Additionally, the presence of background noise makes hearing with just one ear considerably more challenging, so a CROS device could be beneficial in any loud environment.

What is BiCROS Hearing Aids?

A BiCROS system works very similarly to a CROS system, except instead of a transmitter worn on the better ear, it is a hearing aid. These systems are for people who have some degree of hearing loss in their better hearing ear.

The signal sent to the better ear, whether it be the transmission from the other side or sound picked up on the good side, is amplified according to the individual’s hearing loss in that ear.

The same situations mentioned above would be improved for a BiCROS user, particularly noisy environments which are already going to be challenging with some degree of hearing loss. 

How Do I Choose CROS vs BiCROS Hearing Aids?

Your audiogram would dictate whether you are a candidate for a CROS or a BiCROS system. Simply put, if your hearing is normal or near normal on the other side, you would be a candidate for a CROS. If you have mild to moderately severe hearing loss on your better side, you would be a candidate for a BiCROS. Your audiologist or other healthcare professional can make a recommendation regarding which CROS or BiCROS system is most appropriate.

Most of the major hearing aid manufacturers offer these systems, and they all function much the same way so your decision would be based on other features such as Bluetooth compatibility, aesthetic preference, rechargeability, waterproof capabilities, and your provider’s preference. 

Alternatives To CROS or BiCROS Hearing Aids

It is important to know that these are not your only options for amplification as a person struggling with single-sided deafness. There are two other options available: bone-anchored hearing aids and cochlear implants

Bone conduction hearing aids work by directly stimulating the inner ear (cochlea) via vibrations in the temporal bone rather than using the traditional hearing pathway (ear canal, middle ear, inner ear). The first iterations of bone conduction hearing aids involved undergoing a surgical procedure to have a small screw, known as an abutment, placed in the temporal bone to hold the device in place.

Other devices are now fully implanted under the skin and attach to the external portion via a magnet, and still others utilize a medical grade sticker to hold the device in place. Often when children are deemed candidates for a bone conduction hearing aid, they start by wearing it in a headband. This is a way to test the efficacy of the device and avoid surgery at a young age, if possible.

The bone conduction hearing device itself has microphones like traditional hearing aids, and the amplification is delivered based on the patient’s degree of sensorineural hearing loss. Because the hearing organs are housed within the temporal bone and respond to vibrations, the better cochlea will always respond even if sound is technically presented to the contralateral side. Using a bone anchored hearing aid would ensure that sound reaches the normal or near-normal cochlea, regardless of one side being completely deafened.

Cochlear implants are comprised of two main parts: the internal cochlear stimulator, which is surgically placed under the skin and encompasses the internal electronics and the electrode array which is inserted into the cochlea, and the external speech processor which contains the microphones to capture sound. The acoustic sound from the environment is converted into electrical impulses which are delivered to the electrode array inside the cochlea, stimulating the auditory nerve and sending sound to the brain.

Cochlear implants restore access to sound for patients who can no longer derive adequate benefit from traditional hearing aids. Cochlear implants do not sound like hearing aids or like normal hearing, due to the difference in sound pathway and method of stimulating the auditory nerve. However, the brain is incredibly plastic and can adjust to the new input, allowing patients who had very poor speech understanding with hearing aids to substantially improve their ability to hear in a variety of listening environments.

Patients with a “dead ear” should consider a cochlear implant. Increasingly, insurance companies are providing coverage for cochlear implants in cases of single-sided deafness due to the overwhelmingly positive outcomes for these patients. It is more difficult (but not unheard of) to obtain insurance approval when you have a normal-hearing ear on the other side. You can talk to your provider about specific challenges you are experiencing, as they will likely include these examples in the letter of medical necessity they write to obtain prior authorization.

If there issue some degree of hearing loss on the other side, you can continue to use a hearing aid with your cochlear implant as a “bimodal” system. Outcomes with a cochlear implant are influenced by several factors, so talk with your provider about your specific etiology and duration of hearing loss in the poorer ear to see whether this is a viable option.

Often CROS and BiCROS are seen as the low-risk, non-surgical option to try first for patients who are experiencing single-sided deafness. You can talk to your provider about trialing a system to see if it works well for you if you are concerned about moving forward with a bone-anchored option or a cochlear implant.

CROS or BiCROS Hearing Aid Takeaway

One important thing to know about these systems is that they will not allow you to localize where sound is coming from, because all input will go to the better-hearing ear. This can be quite disorienting early on, though many patients report that they are able to adjust over time.

Patients may also still find that they need eye contact and other visual cues in order to understand speech; simply having the transmitted sound (such as in the example of driving a car) is not adequate for full understanding. It is important to advocate for yourself with family, friends, and coworkers to explain how the system works and that it may still help for them to be on your preferred side.

The primary adjustments made to the system by your audiologist would be to the actual hearing aid, in the case of a BiCROS system. For a CROS, the audiologist can adjust the balance and volume of the sound being delivered to the better ear. Additionally, many of the systems now have sophisticated directional microphone technology so that the device microphones can focus forward in noisy situations and try to eliminate some background noise.

If you are experiencing any degree of hearing loss, the first step is to consult an audiologist or other hearing health professional for a diagnostic audiogram. Based on your test results, the professional will be able to lay out your options in terms of traditional hearing aids, CROS/BiCROS, bone-anchored hearing aids, and cochlear implants.

Often in cases of single-sided deafness, a medical referral is warranted to determine or confirm the cause of the asymmetry between the two ears. Depending on your etiology and duration of hearing loss as well as your lifestyle, preferences, and overall health, you may have several different options at your disposal. Find a professional you trust and let them help guide you through this decision making process, and you will likely find substantial improvement in listening situations that were previously very difficult when relying solely on one ear.

erin edwards aud
Clinical Audiologist at Towson University | + posts

Erin Edwards received her Doctor of Audiology degree from Towson University in 2015 and her Ph.D. in Education and Leadership from Pacific University in 2022. She has worked with patients of all ages in a variety of settings and has a specific interest in cochlear implants, the relationship of hearing loss and dementia, and interdisciplinary healthcare.

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