152. Hearing Defects and Hearing Tests – Quiz

📌 Professor’s Notes: Quick Revision

High-yield revision notes for rapid review before university examinations.

• Deafness means partial or complete loss of hearing. It is classified into conductive, sensorineural and mixed hearing loss, depending on the site and nature of the lesion.
• Conductive hearing loss results from impaired sound transmission through the external or middle ear. The cochlea and auditory nerve remain functional, so bone conduction is relatively preserved. Common causes include impacted wax, foreign bodies, tympanic membrane damage, otitis media, ossicular disruption, otosclerosis and Eustachian tube dysfunction.
• Sensorineural hearing loss results from damage to the cochlea, auditory nerve or central auditory pathways. Important causes include ototoxic drugs, aging-related degeneration of hair cells (presbycusis), chronic loud-noise exposure, vestibular schwannoma, head trauma, labyrinthitis and Ménière disease.
• Mixed hearing loss contains both conductive and sensorineural components. It may occur when disorders affect both the middle and inner ear, such as chronic infection or trauma.
• Tinnitus is the perception of sound without an external acoustic stimulus. Patients may describe ringing, buzzing, roaring or hissing. It can occur with either conductive or sensorineural hearing loss.
• Treatment depends on the cause. Conductive loss may improve after removing wax or foreign bodies, treating infection, or repairing the tympanic membrane or ossicles. Hearing aids amplify sound, whereas cochlear implants directly stimulate the cochlear nerve and may benefit selected patients with severe to profound sensorineural loss.
• Initial hearing assessment includes examination of the external ear and tympanic membrane, followed by bedside testing. Rinne, Weber and Schwabach tests are commonly performed with 256- or 512-hertz tuning forks.
• Rinne test compares air conduction with bone conduction in the same ear. Normally, air conduction is better than bone conduction. In conductive hearing loss, bone conduction becomes better than air conduction. In sensorineural loss, both are reduced, but air conduction remains better than bone conduction if the loss is incomplete.
• Weber test compares bone-conducted sound between the two ears. It is heard equally in normal hearing. The sound lateralizes to the affected ear in conductive loss and to the normal ear in sensorineural loss.
• Schwabach test compares the patient’s bone conduction with that of a person with normal hearing. Prolonged bone conduction suggests conductive loss, whereas shortened bone conduction suggests sensorineural loss. It is now used less frequently.
• Pure tone audiometry is the most widely used subjective hearing test. Different frequencies are presented separately to each ear, and the lowest intensity detected is recorded as an audiogram. Comparing air- and bone-conduction thresholds helps identify conductive, sensorineural and mixed losses.
• Brainstem auditory evoked responses record electrical activity along the auditory pathway after brief sound stimulation. Waves I–V represent successive levels from the auditory nerve to the inferior colliculus. Wave V is the most clinically reliable. This test is particularly useful in newborns, infants, uncooperative patients and suspected brainstem lesions.
• Otoacoustic emissions are low-intensity sounds produced by active outer hair cells. Their presence indicates functioning outer hair cells, while their absence suggests cochlear dysfunction. They are rapid, non-invasive and widely used for newborn hearing screening.