Eye care practitioners see patients on a regular basis so are ideally placed to detect conditions other than just those specific to the eye that might otherwise not be directly reported. They can then ensure that patients understand that help is available and how this might be sought.

Hearing loss occurs for many reasons, is often age-related and in many cases linked with sight loss. Furthermore, loss is often insidious in onset and may be causing problems for individuals and the people around them in a way that they might not easily pinpoint. Eye care practitioners should be aware of the nature of hearing loss, be able to identify patients where there may be a concern, and know the best advice to help the patient address the deficit. It is also essential to be able to communicate effectively with patients who have hearing loss in order to provide adequate eye care. This article is an overview of hearing loss and aims to offer the essentials that should be useful to all categories of registered eye care practitioner.

The extent of the problem

Here are a few current facts compiled by the UK charity Action on Hearing Loss (formerly the Royal National Institute for the Deaf).

  • There are more than 11 million people in the UK with some form of hearing loss, or one in six of the population (figure 1).
  • By 2035, it is estimated that there will be 15.6 million with hearing loss in the UK – one in five people.
  • Hearing loss is becoming more prevalent, not just related to increased life expectancy, but part linked with the noisy modern world.
  • More than 900,000 people in the UK are severely or profoundly deaf.
  • There are more than 45,000 deaf children in the UK, plus many more who experience temporary hearing loss.
  • More than 70% of over 70-year-olds and 40% of over 50-year-olds have some kind of hearing loss.
  • 24,000 people across the UK use sign language as their main language – although this is likely to be an underestimate.
  • There are approximately 250,000 people in the UK with both hearing loss and sight loss. Of these 220,000 are aged 70 or ever.
  • Around 6.7million people could benefit from hearing aids.
  • On average it takes 10 years for people to address their hearing loss.
  • Around one in every 10 UK adults has tinnitus. This increases to 25-30% of over 70-year-olds.
  • 45% people who report hearing problems to their GP but are not referred for a hearing test or hearing aids.

Figure 1: Prevalence of hearing loss in the UK

Normal hearing

Humans having two ears helps in the localisation of sound and, indeed, has links with the visual system to help develop an accurate overall percept. Each comprises an outer ear, or pinna, middle ear and inner ear (see figure 2).

Figure 2: Gross anatomy of the ear

Sound is a compression wave requiring a medium for transmission (‘in space no one can hear you scream’). The frequency of the compressions in the medium dictates the pitch of the sound and the human ear of a young person can detect frequencies from 20Hz to 20,000Hz. The difference in pressure between the compression and the gap in between is the amplitude and this dictates the volume or loudness. Loudness is measured in decibels (a logarithmic expression of the amplitude ratio). Normal speech is around 65dB and noise of 120dB or more may cause pain or damage to the ear. Loudness is further influenced by the frequency, with humans having a peak sensitivity to frequencies of 3,000Hz.

The pinna is designed to capture sound waves (analogous with, say, a satellite dish for radio waves) and funnel them into the ear canal (or external auditory meatus) within which the sound resonates and causes the eardrum (or tympanic membrane), which separates the outer and middle ear to vibrate in a way dictated by the nature of the pressure wave (analogous to the membrane on a loudspeaker).

The middle ear contains three linked bones or ossicles which link the eardrum to the oval window at the start of the inner ear. These bones, the malleus, incus and stapes, are, as every pub quizzer knows, the smallest bones in the body and amplify the incident pressure wave. Two muscles, the tensor tympanum and the stapedius, attach to the bones and dampen any extreme bone vibration. Air is directly available to the middle ear via the Eustachian tube from the pharynx so that ambient air pressure either side of the eardrum is maintained in equilibrium. Sudden pressure changes, as during a flight, is noticed as ‘ear popping’ during the equalisation process. The oval window is twenty times smaller than the eardrum and this greatly increases the pressure waves reaching the inner ear.

The inner ear is essentially a system of fluid filled tubes forming two distinct structures:

  • the cochlea – a snail-like whorled structure which converts the pressure waves into electric signals then transmitted to the brain.
  • the vestibular apparatus – three semi-circular tubes filled with fluid and orientated to represent the three spatial dimensions. Fluid movements relative to the head’s position and this movement is converted into electrical signals representing the head’s position in space

Figure 3 shows a cross section of the cochlea and it is seen to have three chambers. The upper chamber, the scala vestibule, is directly linked to the oval window and fluid within transmits the incident pressure wave along the cochlea which then returns back along the lower chamber, the scala tympani, to be dispersed via a second, round, window. Pressure waves are transmitted to the middle chamber, the cochlear duct, via the basilar membrane upon which lies the organ of Corti. This contains hair cells of ascending height along the cochlear length and these are able to resonate at individual frequencies dictated by their length. This is how individual frequencies stimulate specific neural signals to the brain, transmitted via the cochlear division of the 8th (vestibulocochlear or auditory) cranial nerve. The other division is linked to the vestibular apparatus.

Figure 3: Anatomy of the cochlea

Auditory signals pass via the lateral meniscus and inferior colliculi, the medial geniculate nucleus to the primary auditory cortex (for sound recognition) in the temporal lobe. The adjacent secondary auditory cortex is involved in sound localisation, language and music perception.

Understanding the anatomy helps explain the various causes of hearing loss.

Causes of hearing loss

Essentially there are two types of hearing loss:

  • Conductive – usually localised to the outer and middle ear, a blockage or structural change prevents conduction of the compression wave adequately to the cochlea. Sound is reduced or muffled. Depending on the underlying cause, conductive hearing loss may be reversible.
  • Sensorineural – damage to the cochlea or auditory neural pathway preventing adequate transmission of neural signals to the brain. Such loss is permanent.

Where both processes occur, the result is described as mixed hearing loss. Let us briefly describe some common causes of the above

  • Ear wax – secretions from the wall of the ear canal have an antiseptic role and help remove foreign particulate matter. Aggregations form a wax-like substance, of amounts related to individual’s skin type, and can block the canal and disrupt compression wave resonance. It is easily identified by an otoscope, and removed by loosening drops (olive oil is useful) or in stubborn cases, syringing. The latter is not possible where there has been damage to the eardrum (say, after a very loud noise insult) and specialist intervention is needed. Syringing needs to use sterile fluid of body temperature otherwise convection currents are set up in the vestibular apparatus causing dizziness and even nausea. This is exploited when a specialist wants to assess the health of the vestibular apparatus (the Caloric test).
  • Otitis externa – inflammation of the outer ear caused by infections, skin disorders (such as eczema and psoriasis) or allergy. Swelling and discharge disrupt sound conduction. Treatment is specific to the cause.
  • Exostosis – bony growths within the canal that may develop with repeated exposure to cold water. Surgery may be needed to restore uninterrupted conduction, but avoidance is the best policy (earplugs for swimming, for example).
  • Otitis media – middle ear infections. These may spread from the nose or throat via the Eustachian communication. Most common in youngsters, infection may cause the eardrum to bulge causing severe earache dampening of sound through restriction of the movement of the ossicles. Treatment is specific to the underlying infection. Otitis media is often followed by a build-up of fluid (glue ear) which has not drained away via the Eustachian tube and so continues to muffle sound. Persistence for some months might require surgical installation of a drainage tube or grommet in the eardrum. Repeated otitis media may result in longer term fluid build-up (called chronic suppurative otitis media or CSOM) or a skin growth in the middle ear called a cholesteatoma. Surgery is typically needed to treat this.
  • Ossicle damage – either congenital malformation or damage through injury or serious infection prevents normal bone transmission of sound signals. Surgical treatment includes implantation of artificial replacements. Sometimes the bones, especially the stapes, become restricted or even fixed by abnormal bone growth (otosclerosis). The condition is most common in women aged 20 to 30 and is exacerbated by pregnancy. Hearing aids may help, but a complete stapendectomy is sometimes required to restore adequate hearing.
  • Perforated eardrum – trauma, sudden extreme pressure changes (such as from an explosion) and serious infections may perforate the drum and cause earache. This usually resolves in a month or two during which the ear must be protected from water and external fluid ingression.

Sensorineural loss

Applying a resonating tuning fork to the mastoid bone may allow a patient with no sensorineural loss to hear the sound even though conductive loss prevents them from hearing it when held close to the ear (Rinne’s test). If not, then sensorineural loss is likely. If the tuning fork is applied to the middle of the forehead, asymmetry in sound indicates either conductive loss in the poorer ear or sensorineural loss in the other. This may then be confirmed by covering the weaker ear and total loss of sound then confirms the latter (Weber’s test). The nature of the loss may be further investigated by seeing which frequencies the patient has lost sensitivity to – this is audiometry.

Figure 4: Sensory loss – normal sensory tissue left, damaged tissue right

Just as presbyopia (‘presby’ or older and ‘opia’ sightedness) reduces our focusing ability as we age, similarly, ageing leads to a loss of high frequency responsive hair cells (figure 5) in the cochlea (presbycusis). Obviously, loud insult hastens this damage, hence restrictions on noise levels. Occasionally disease or damage or stimulus loss triggers spontaneous neural firing causing ‘ringing’ or tinnitus, a sort of aural Charles Bonnett. High frequency loss is particularly difficult as it means that we lose out on many of the consonants and higher pitched phonemes in the English Language. This means that a person with a high frequency loss can experience sound coming through like it is a string of vowels and low pitched sounds which is what makes it sound like someone is mumbling (see figure 5). As a result, people living with this type of loss tend to blame other people for not speaking clearly and do not realise it is their hearing. It is also this loss with age that is widespread and of which we should all be aware when dealing with older patients.

Figure 5: High frequency loss impacts upon consonants – the lower construct is harder to interpret

People with sensorineural loss usually benefit greatly from hearing aids and it may improve someone’s quality of life if this is made known to them. Severe cases of cochlear disruption may require a cochlear implant.

Other important causes worthy of note for the eye care practitioner include:

  • Space occupying neoplasms impacting upon the auditory nerve (often somewhat erroneously called an acoustic neuroma but more correctly is a vestibular schwannoma as it results from excess Schwann cell growth on the vestibular nerve) may cause hearing loss, tinnitus, balance issues and are a cause of headache that may prompt an eye examination. Though slow growing, symptoms may require surgery which can result in loss of facial innervation and ocular exposure and lagophthalmos.
  • Some medicines (see table 1 for some examples)
  • Infectious disease – these include mumps and meningitis
  • Meniere’s disease – abnormal fluid levels in the inner ear structures causing hearing loss, tinnitus and balance problems
  • Inherited and congenital syndromes – about 30% of deafness in young children is associated with other medical conditions or ‘syndromes.’ This type of deafness is called ‘syndromic deafness’. These additional conditions are usually of no concern, but it may be important to identify some. For example, someone with Usher syndrome has deafness from birth and loses their sight gradually. Usher’s is the commonest cause of ‘deaf-blindness’ and is usually made known by the patient using a striped white cane to signal their hearing loss concomitant with sight loss. Interestingly, some patients with Duane’s retraction syndrome have other problems, such as hearing impairment, Goldenhar syndrome, spinal and vertebral abnormalities. Referral for sensory assessment is recommended even though little will be done regarding the incomitancy.
  • Birth complications – may cause insult to the auditory pathway.

How to access help

Most hearing loss when first suspected is best assessed by the GP practice. They can check for any treatable causes, such as a build-up of ear wax, or a more concerning disease process requiring attention.

When these have been ruled out or treated, the remaining hearing loss (most likely presbyacutic) requires assessment by an audiologist who will assess the loss and decide upon possible hearing aids. Patients can either be referred to an NHS audiology service for these hearing tests, or go to a private hearing care provider. Any hearing aids they might need will be free from the NHS, but will have to pay for them if going private. Hearing aids will be discussed in a future article.

Under a scheme called Any Qualified Provider (AQP), some private hearing care providers also deliver NHS adult-audiology services. This means that if the scheme is available in a patient’s area, and they meet the criteria, they will have more choice about which NHS audiology service they are referred to.

A ‘Locate and Rate’ tool is available on the Action on Hearing website showing what hearing care services are available to any chosen area. This lets you search for audiology services in your area (private and NHS), and see ratings and comments made by people who have previously visited them.

Communication skills

When communicating with a patient with a hearing impairment in eye care practice, the following general points should be considered:

  • The practitioner should face the patient as much as possible. For times of significant communication, such as during history and symptoms, good lighting on both faces is important.
  • The mouth should be as visible as possible. Some authorities point out that an untrimmed beard or a face covering of any sort may inhibit the interpretation of speech.
  • The practitioner should always attract attention before starting to speak.
  • Any background noise may significantly reduce the ability of the patient in interpreting the message from the practitioner. This is potentially a problem outside the consulting room, for example, at reception or in a pre-examination area.
  • As with most patients, the use of jargon or technical words (astigmatism, amblyopia and so on) adds to confusion.
  • Specific instructions may be reinforced by being written down.
  • Whole sentences are easier to interpret, though verbosity is best avoided.
  • Complex messages, such as at the summing up of the practitioner’s findings, should be given in short concise bundles (categorisation).
  • Speech should be slowed down to a steady well-articulated pace of a sensible volume. If speech is too fast it becomes imperceptible, too slow and the natural rhythm is lost making interpretation harder.
  • Though raising volume a little is helpful, shouting or speaking too loudly will actually distort clear speech and may even be painful (for either party).
  • The practitioner should ascertain whether the patient has asymmetrical hearing loss and arrange to be seated nearer the side with reduced loss.
  • The practitioner should not be shy or embarrassed to repeat important phrases.
  • Speech can be very effectively reinforced by appropriate body language without any need to resort to specialist sign languages.
  • The practitioner must allow adequate time to allow the patient to respond. It is often forgotten that one has to also listen to a hearing impaired patient

Conclusion

This author has long advocated that eye care practitioners are well placed to ask patients whether they have had a cardiovascular health check and this is particularly useful for those patients (middle-aged men) who are at risk of diseases like hypertension but are poor attenders for health checks. In a similar way, we are well placed to let elderly patients know about presbyacusis and let them know that treatment options are available.

Useful resources

actiononhearingloss.org.uk