SN3
SHORT NOTE
5M
★ High-yield
Classify deafness. Describe the tuning fork tests and their interpretation.
Definitions
Deafness = partial or complete loss of hearing.Conductive — a defect in the external or middle ear.Sensorineural — a defect in the cochlea, cochlear nerve or central pathway.
Causes
| Conductive | Sensorineural |
|---|---|
| Wax, foreign body | Presbycusis (age) |
| Otitis media, effusion | Noise-induced |
| Tympanic membrane perforation | Ototoxic drugs — aminoglycosides, furosemide, cisplatin |
| Otosclerosis | Ménière disease |
| Ossicular disruption | Congenital rubella, kernicterus, meningitis |
| Congenital atresia | Acoustic neuroma |
Tuning Fork Tests (512 HZ)
| Test | Method | Normal | Conductive | Sensorineural |
|---|---|---|---|---|
| Rinne | Air conduction vs bone conduction in the same ear | AC > BC (positive) | BC > AC (negative) | AC > BC (positive, but both reduced) |
| Weber | Fork on the vertex; which ear hears it louder | Central — equal in both | Lateralised to the deaf (affected) ear | Lateralised to the normal ear |
| Absolute bone conduction | Compared with the examiner | Equal | Equal | Reduced |
CLINICAL PEARL
Note: in conductive deafness, Weber goes to the bad ear; in sensorineural deafness it goes away from it. This single contrast is the most commonly asked point.
Other Investigations
- Pure tone audiometry — quantifies the loss and shows the air–bone gap that characterises conductive deafness
- Impedance audiometry (tympanometry) — middle ear function and the stapedial reflex
- Otoacoustic emissions — test outer hair cells; used for newborn screening
- Brainstem evoked response audiometry — in infants and in suspected retrocochlear lesions
Applied Aspects
- Otosclerosis — fixation of the stapes footplate; young adults, often worse in pregnancy; treated by stapedectomy
- Universal newborn hearing screening matters because speech development depends on hearing in the first 2 years — late detection means permanent language delay
- Hearing aids help most losses; cochlear implants are used in profound sensorineural deafness where hair cells have failed but the nerve is intact
- Occupational noise limits — 85–90 dB for 8 hours; ear protection and audiometric surveillance are statutory in noisy industry
- Chronic suppurative otitis media is still a common preventable cause of deafness in India
All questions in Special Senses
- Q1Describe the refractive media of the eye and the mechanism of accommodation. Discuss the errors of refraction and their correction. ★
- Q2Compare rods and cones. Describe the mechanism of phototransduction and dark adaptation. ★
- Q3Trace the visual pathway. Describe the effects of lesions at different sites and the pupillary light reflex. ★
- Q4Describe the mechanism of hearing. Explain impedance matching, the transduction by hair cells and the analysis of pitch. ★
- Q5Describe the vestibular apparatus and its role in the maintenance of equilibrium. Add a note on nystagmus and the caloric test. ★
- SN1Describe the physiological basis of colour vision. Classify colour blindness and describe its inheritance. ★
- SN2Describe the formation, circulation and functions of aqueous humour. Add a note on glaucoma. ★
- SN3Classify deafness. Describe the tuning fork tests and their interpretation. ★
- SN4Describe the modalities of taste, the taste buds and the nerve supply of the tongue.
- SN5Describe the mechanism of olfaction and the olfactory pathway. Add a note on anosmia.
- SN6Describe the formation, circulation and functions of aqueous humour and the factors affecting intraocular pressure. ★
- SN7Classify errors of refraction and describe the mechanism of accommodation. ★