Quick questions on Technologies for hearing and vision disorders: HSC Biology Module 8

Sound waves enter the outer ear and vibrate the tympanic membrane. The three ossicles (malleus, incus, stapes) in the middle ear amplify the vibration and transmit it to the oval window of the cochlea. In the cochlea, fluid waves bend the stereocilia of hair cells along the basilar membrane. Hair cells convert mechanical movement into electrical signals carried by the auditory nerve to the brain.

Conductive hearing loss. Sound transmission through the outer or middle ear is blocked or reduced. Causes include ear wax, otitis media, perforated eardrum and otosclerosis (ossicle stiffening).

Hearing aids. Amplify incoming sound. Modern digital hearing aids have a microphone, amplifier, speaker (receiver) and battery, with software that selectively amplifies speech frequencies and suppresses background noise. Effective for mild to moderate hearing loss where hair cells still function.

Light enters through the cornea (the main refracting surface, providing about two-thirds of the eye's focusing power). The pupil controls light intake; the iris adjusts pupil diameter. The lens fine-tunes focus through accommodation (changing shape via the ciliary muscle). The retina contains photoreceptors (rods for low light, cones for colour).

Myopia (short-sightedness). Eye too long or cornea too curved; light focuses in front of the retina. Distant objects are blurred. Highly prevalent and rising; almost half of young adults globally.

Corrective lenses (spectacles). External refracting lenses placed in front of the eye. A concave (negative power) lens diverges light to correct myopia; a convex (positive power) lens converges light to correct hyperopia; a cylindrical lens corrects astigmatism; multifocal or progressive lenses correct presbyopia.

Sound transmission through the outer or middle ear is blocked or reduced. Causes include ear wax, otitis media, perforated eardrum and otosclerosis (ossicle stiffening).

Damage to the cochlear hair cells or auditory nerve. Causes include age-related (presbycusis), noise exposure, ototoxic drugs (some antibiotics, cisplatin) and genetic conditions.

Both conductive and sensorineural components.

Amplify incoming sound. Modern digital hearing aids have a microphone, amplifier, speaker (receiver) and battery, with software that selectively amplifies speech frequencies and suppresses background noise. Effective for mild to moderate hearing loss where hair cells still function.

Used for conductive loss when the outer or middle ear is non-functional. A titanium implant in the skull conducts sound vibrations through bone directly to the cochlea, bypassing the middle ear.

Used for severe to profound sensorineural hearing loss. Components and mechanism are described in the past-question answer above. The implant bypasses damaged hair cells by directly stimulating the auditory nerve through an electrode array in the cochlea.

A small actuator attached to the ossicles vibrates them mechanically. Used when conventional hearing aids cause feedback or skin reactions.

Eye too long or cornea too curved; light focuses in front of the retina. Distant objects are blurred. Highly prevalent and rising; almost half of young adults globally.

Eye too short or cornea too flat; light would focus behind the retina. Near objects are blurred.