Iatrogenic hearing loss occurs as an undesirable side effect of medical interventions or therapies, such as ototoxic drugs (aminoglycosides, cisplatin) or damage during ear surgery. Hair cells in the inner ear or synaptic connections are often affected, which can lead to permanent sensorineural hearing loss. As a preventive measure, drug doses are monitored and substances that protect against otoxicity are considered. Once iatrogenic damage has occurred, early hearing rehabilitation with hearing aids or implants helps. Interdisciplinary coordination between ENT, oncology and audiology minimizes risks.

Idiopathic hearing loss is a hearing loss of unknown cause where there are no organic findings or known risk factors. It can occur suddenly (idiopathic sudden deafness) or gradually and usually affects high frequencies. The diagnosis includes extensive imaging procedures, laboratory analyses and otoacoustic emissions, but often remains inconclusive. Therapeutic treatment is similar to that for sudden deafness with corticosteroids and vasodilators. Long-term management includes monitoring and, if necessary, hearing aid fitting.

An in-the-ear hearing aid sits completely in the ear canal and is barely visible from the outside. It uses the natural sound funnel effect of the outer ear and offers good sound, but is less powerful than BTE devices. Due to the compact design, battery capacity and amplification reserves are limited, which makes BTEs particularly suitable for mild to moderate hearing losses. Fitting requires precise earmolds and regular maintenance to avoid cerumen blockages. Users appreciate discretion and wearing comfort.

The IIC hearing aid (Invisible-in-Canal) is a sub-form of the ITE and sits deep in the ear canal just in front of the eardrum. It is almost invisible and offers optimized speech intelligibility thanks to minimal feedback. The smallest microphones and amplifier technology enable multi-channel signal processing despite the compact design. Limitations exist in the case of severe hearing loss and ease of use (e.g. changing batteries). Hygienic cleaning and regular checks are essential to avoid loss of performance.

Impedance describes the resistance and reactance of an acoustic or mechanical system to sound transmission, measured in ohms or mmho. In the ear, it refers to the eardrum and middle ear chain, whose mobility is examined when pressure changes (tympanometry). Changes in the impedance curve indicate fluid accumulation, stiffening or perforations. In hearing aid technology, impedance measurement is used to check the fit of earmolds. Optimal impedance matching maximizes sound conduction efficiency.

An impulse noise is a short, sudden increase in sound pressure, such as a bang or thud, with a broadband frequency spectrum. Such stimuli can cause acoustic trauma when peak levels exceed 140 dB SPL. In audiometry, impulse noise is used to test the stapedius reflex and hearing protection reflex. Hearing protection for impulse noise differs from continuous sound protection as rapid attenuation responses are required. Research investigates material dynamics and reflexive mechanisms to protect against impulse damage.

In-situ measurements are carried out directly in the fitted state, e.g. OAE or HRTF measurements in the ear canal with the hearing aid inserted. They allow realistic recording of amplification and filter effects under fitting conditions. Unlike free-field measurements, in-situ methods take individual ear anatomy and earmold effects into account. Modern fitting software integrates in-situ data for precise fine calibration. Regular in-situ checks ensure long-term fitting quality.

Infrasound refers to sound with frequencies below 20 Hz, which are below the human hearing threshold but can produce physically perceptible vibrations. Sources are natural phenomena (earthquakes, wind) and technical installations (wind power, industry). Long-term exposure can cause discomfort, a feeling of pressure in the ear and sleep disturbances. Standardized measurement methods and filter techniques help to detect and attenuate infrasound. Researchers are investigating the effects of infrasound on vestibular functions.

An incomplete stapedius reflex occurs when the stapedius muscle only partially contracts in response to loud stimuli. Audiologically, this leads to reduced attenuation of the ossicular chain and an increased risk of noise damage. Incomplete reflexes indicate muscle dysfunction, nerve lesions or middle ear diseases. Reflex testing with tympanometry quantifies amplitude and latency. Therapeutically, hearing aid compression and muscle training can support reflex amplification.

The inner ear consists of the cochlea and vestibular organ and converts mechanical sound and movement stimuli into electrical nerve impulses. In the cochlea, hair cells are located on the basilar membrane, which are stimulated differently depending on the frequency. The vestibular organ registers head movements and position. Fluid-filled scales and membranes ensure electrochemical transduction. Injuries or degeneration here lead to sensorineural hearing loss and dizziness.

Sensorineural hearing loss is caused by damage to the hair cells, auditory nerve or central auditory pathways. It manifests itself in increased hearing thresholds and reduced speech comprehension, especially in noise. Causes include age, noise trauma, genetic factors or ototoxins. Therapy includes hearing aids, cochlear implants and auditory training. Research into hair cell regeneration and synaptic protection is aimed at finding a cure.

The inner hair cells are primary sensory cells of the cochlea that convert sound-induced membrane movements into electrical signals. They are individually connected to afferent nerve fibers and are crucial for sound and speech intelligibility. Loss or dysfunction of the IHC leads to severe sensorineural hearing loss. Unlike outer hair cells, they cannot regenerate in humans. Gene therapy and stem cell approaches are researching repair methods.

Insufficiency of the auditory tube (Eustachian tube) causes the ventilation mechanism to fail and pressure equalization between the middle ear and the pharynx does not work. This leads to chronic negative pressure, effusion and hearing loss. Symptoms include a feeling of pressure, crackling and recurrent otitis. Diagnosis by tube function test and tympanometry; treatment includes balloon dilatation, catheter and tympanostomy tubes. Long-term insufficiency requires interdisciplinary care.

An integrated tinnitus noiser is a function in modern hearing aids that emits a quiet noise signal directly from the device to mask or desensitize tinnitus. The noise profile can be individually adjusted in terms of frequency spectrum and volume. Continuous noise playback promotes habituation and reduces the perception of tinnitus in everyday life. Users can activate masking programs depending on the situation. Studies show that integrated noisers improve sleep and quality of life.

Intensity describes the power per unit area of a sound wave and is usually expressed in watts per square meter (W/m²) or in decibels (dB SPL). It correlates with the perceived loudness, whereby a tenfold increase in sound intensity corresponds to an increase of 10 dB. In the ear, high intensities lead to greater deflection of the eardrum and basilar membrane, which can lead to hair cell damage if the pain threshold is exceeded. The intensity-loudness function is determined audiologically in order to determine the dynamic range and comfort threshold. Hearing aids use this knowledge for compression algorithms that attenuate loud signals and amplify quiet ones.

The Interaural Level Difference is the level difference of a sound signal between the right and left ear, caused by the head shadow effect. ILD serves as an important indicator for the horizontal localization of high frequencies (>1.5 kHz). In the superior olive nucleus, ILD information is combined with time differences to enable spatial hearing. Hearing aids with binaural networking receive ILD cues by synchronously exchanging level information. ILD tests in anechoic chambers quantify localization efficiency.

Die Interaurale Zeitdifferenz ist die Differenz in der Ankunftszeit eines Schallsignals an beiden Ohren und dient primär der Lokalisation tiefer Frequenzen (<1.5 kHz). Bereits Mikrosekundenunterschiede reichen aus, damit das Gehirn Schallquellen präzise ortet. ITD‑Verarbeitung erfolgt im medialen Olivenkern, wo phase-locked Neurone unterschiedliche Verzögerungen vergleichen. Störungen der ITD-Verarbeitung führen zu Lokalisationseinschränkungen und schlechterem Sprachverstehen in Lärm. Hörsysteme müssen Latenzen minimieren, um natürliche ITD‑Cues nicht zu verfälschen.

An intracochlear electrode is part of a cochlear implant and is inserted into the cochlea through a cochleotomy. It electrically stimulates specific regions of the cochlea and replaces defective hair cells. The number and distribution of the electrodes determines the spectral resolution of the implant. Surgical precision during insertion minimizes trauma and preserves residual hearing. Post-operative mapping adjusts stimulation levels per electrode for optimal speech understanding.

The intralabyrinthine pressure refers to the hydrostatic pressure of the endolymphatic and perilymphatic spaces in the inner ear. Changes, for example in Meniere's disease, lead to hydrops and cause dizziness, tinnitus and hearing loss. Pressure measurements in animal models help to understand pathomechanisms and develop pressure regulation methods. Clinically, tympanometry and ECochG are used to indirectly infer intralabyrinthine pressure. Therapeutic approaches aim to relieve pressure through diuretics or surgical decompression.

During intraoperative monitoring, evoked brainstem potentials (ABR) are continuously recorded during ear or skull base surgery. This protects against damage to the auditory nerve and brainstem structures by detecting loss of function at an early stage. Neurophysiologists adjust stimulation and recording parameters in real time. Failures or changes in latency trigger immediate pauses in surgery or adjustments to the technique. The procedure increases safety during acoustic neuroma resections and cochlear implantations.

Intratympanic gentamicin therapy is used to treat refractory Meniere's disease by selectively injecting the antibiotic into the middle ear. Gentamicin diffuses through the eardrum into the cochlea and selectively destroys vestibular hair cells to reduce vertigo attacks. The dose is carefully titrated to minimize hearing loss. Follow-up includes audiometric checks and vestibular function tests. The therapy provides effective dizziness control with low systemic toxicity.

Ionotoxicity refers to the damage to hair cells and nerve cells in the ear caused by certain ion-mediated substances, such as aminoglycosides or cisplatin. These ototoxins increase calcium permeability and generate reactive oxygen species, which leads to cell death. Early detection is achieved by DPOAE monitoring during therapy. Protective strategies include antioxidants and calcium channel blockers. Long-term effects range from tinnitus to permanent hearing loss.

Ipsi-lateral hearing describes perception at the same ear as the sound source, contralateral hearing at the opposite ear. This dichotomy is central to localization and binaural processing. In diagnostics, ipsi- and contralateral reflexes (stapedius) are tested to detect lateralized pathologies. Differences in thresholds or reflex responses indicate nerve lesions or middle ear disease. Rehabilitation aims to compensate for lateral deficits through binaural treatment.

An isochronous loudness scale ranks sounds of equal perceived loudness across different frequencies. It is based on psychoacoustic data and shows that the human ear is most sensitive at medium frequencies. Isochronous curves (Fletcher-Munson curves) are used to calibrate audiometers and for weighting (A, C filters) in sound level meters. In hearing aid fitting, they help to ensure the comfort and naturalness of the auditory impression.

Isochronic tinnitus is a rhythmic ear tone that is perceived synchronously with the heartbeat ("pulsatile tinnitus"). It is caused by vascular turbulence or pressure fluctuations in the inner ear. Diagnosis includes Doppler sonography and MRI angiography to rule out vascular causes. Treatment depends on the cause, e.g. embolization or pressure therapy. As it is linked to the cardiovascular system, it requires interdisciplinary clarification.