Iatrogenic hearing loss occurs as an undesirable side effect of medical procedures 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, medication doses are monitored and ototoxicity-protective substances are considered. After iatrogenic damage has occurred, early hearing rehabilitation with hearing aids or implants can help. Interdisciplinary coordination between ENT, oncology, and audiology minimizes risks.

Idiopathic hearing loss refers to hearing loss of unknown cause, with no organic findings or known risk factors. It can occur suddenly (idiopathic sudden hearing loss) or gradually and usually affects high frequencies. Diagnostics include extensive imaging procedures, laboratory analyses, and otoacoustic emissions, but often remain inconclusive. Similar to sudden hearing loss, it is treated with corticosteroids and vasodilators. Long-term management includes monitoring and, if necessary, hearing aid fitting.

An ITE (in-the-ear) hearing aid sits completely inside 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 quality, but is less powerful than BTE devices. Due to its compact design, battery capacity and amplification reserves are limited, making ITE devices particularly suitable for mild to moderate hearing loss. Fitting requires precise earmolds and regular maintenance to prevent cerumen blockages. Users appreciate its discretion and comfort.

The IIC (Invisible-in-Canal) hearing aid is a subtype of the ITE and sits deep in the ear canal just in front of the eardrum. It is virtually invisible and offers optimized speech intelligibility thanks to minimal feedback. Despite its compact design, tiny microphones and amplifier technology enable multi-channel signal processing. There are limitations in cases of severe hearing loss and usability (e.g., battery replacement). Hygienic cleaning and regular checks are essential to prevent performance losses.

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 during 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 ear molds. Optimal impedance matching maximizes sound conduction efficiency.

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

In-situ measurements are performed directly in the installed 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 into account individual ear anatomy and otoplasty effects. Modern fitting software integrates in-situ data for precise fine calibration. Regular in-situ checks ensure long-term quality of care.

Infrasound refers to sound with frequencies below 20 Hz, which are below the human hearing threshold but can produce physically perceptible vibrations. Sources include 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. Research is investigating the effect of infrasound on vestibular functions.

An incomplete stapedius reflex is evident 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-induced hearing loss. Incomplete reflexes indicate muscle dysfunction, nerve lesions, or middle ear disorders. Reflex testing with tympanometry quantifies amplitude and latency. Therapeutically, hearing aid compression and muscle training can support reflex enhancement.

The inner ear consists of the cochlea and vestibular organ and converts mechanical sound and movement stimuli into electrical nerve impulses. The cochlea contains hair cells 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 vertigo.

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

The inner hair cells are the primary sensory cells of the cochlea, converting 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 being researched as methods of repair.

Insufficiency of the Eustachian tube causes the ventilation mechanism to fail, preventing pressure equalization between the middle ear and the throat. This leads to chronic negative pressure, fluid buildup, and hearing loss. Symptoms include a feeling of pressure, crackling, and recurrent otitis. Diagnosis is made using a tube function test and tympanometry; treatment includes balloon dilation, catheters, and ear tubes. Long-term insufficiency requires interdisciplinary care.

An integrated tinnitus noiser is a feature in modern hearing aids that emits a soft 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 noiser playback promotes habituation and reduces tinnitus perception in everyday life. Users can activate masking programs depending on the situation. Studies show that integrated noise generators 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, with a tenfold increase in sound intensity corresponding to an increase of 10 dB. In the ear, high intensities cause greater deflection of the eardrum and basilar membrane, which can lead to hair cell damage if the pain threshold is exceeded. Audiologists determine the intensity-loudness function to determine the dynamic range and comfort threshold. Hearing aids use this knowledge for compression algorithms that attenuate loud signals and amplify quiet ones.

Interaural level difference is the difference in sound level between the right and left ears 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, thereby replacing defective hair cells. The number and distribution of the electrodes determine the spectral resolution of the implant. Surgical precision during insertion minimizes trauma and preserves residual hearing. Postoperative mapping adjusts stimulation levels per electrode for optimal speech comprehension.

Intralabyrinthine pressure refers to the hydrostatic pressure of the endolymphatic and perilymphatic spaces in the inner ear. Changes, such as those seen in Meniere's disease, lead to hydrops and cause vertigo, tinnitus, and hearing loss. Pressure measurements in animal models help to understand pathomechanisms and develop pressure regulation procedures. Clinically, intralabyrinthine pressure is indirectly inferred via tympanometry and ECochG. Therapeutic approaches aim to relieve pressure through diuretics or surgical decompression.

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

Intratympanic gentamicin therapy is used to treat refractory Meniere's disease by injecting the antibiotic directly 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 offers effective vertigo control with low systemic toxicity.

Ion toxicity refers to 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, leading to cell death. Early detection is achieved through DPOAE monitoring during therapy. Protective strategies include antioxidants and calcium channel blockers. Long-term effects range from tinnitus to permanent hearing loss.

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

An isochronic 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 mid-range frequencies. Isochronic 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 comfort and naturalness of hearing.

Isochronic tinnitus is a rhythmic sound in the ear that is perceived in sync 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. Since it is linked to the cardiovascular system, it requires interdisciplinary clarification.