**Core Concept:** Otoacoustic emissions (OAEs) are sound waves generated within the inner ear and are considered an indirect measure of cochlear function. They are typically elicited as a response to the mechanical activity of outer hair cells. Otoacoustic emissions can be classified into two types: transient evoked otoacoustic emissions (TEOAEs) and distortion product otoacoustic emissions (DPOAEs).

**Why the Correct Answer is Right:**

Correct Answer: **D. Otoacoustic emissions are useful in ototoxicity monitoring.**

The correct answer is D because otoacoustic emissions are particularly valuable in assessing the risk and progression of ototoxicity in patients undergoing certain medications or treatments known to damage the cochlea. Ototoxicity refers to the damage to the inner ear caused by certain medications or substances. Monitoring cochlear function through otoacoustic emissions allows for early detection of potential ototoxic effects, enabling timely adjustments to therapy or preventive measures.

**Why Each Wrong Option is Incorrect:**

A. **Are accousted by product of outer hair cell - (B)**: Although outer hair cells contribute to the generation of OAEs, option A is too specific, as OAEs can also be generated by inner hair cells and are influenced by factors beyond just outer hair cells.

B. **Are accousted by product of inner hair cell - (C)**: Similar to option A, this statement is too specific and does not encompass the full complexity of OAEs and their generation within the cochlea.

C. **Used as a screening test of hearing in newborn infant - (C)**: While otoacoustic emissions are indeed used as a screening tool for hearing loss in newborns, this option is too narrow, as they have broader applications in assessing cochlear function and ototoxicity monitoring.

E. **Disappear in 8th nerve pathology - (E)**: While OAEs can be affected by 8th nerve pathology, this statement is too specific and does not encompass the full range of factors that can impact OAEs, such as medication-induced ototoxicity or cochlear damage.

**Clinical Pearl:**

Otoacoustic emissions play a crucial role in assessing cochlear function and detecting ototoxicity, making them a valuable tool in clinical practice. Early recognition of ototoxicity through otoacoustic emissions can lead to adjustments in therapy or preventive measures, improving overall patient care and outcomes.