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

Conductive hearing loss. Sound transmission through the outer or middle ear is blocked or reduced - the conducting apparatus is at fault while the cochlea still works. Causes: ear wax, otitis media (middle-ear fluid), a perforated eardrum, or otosclerosis (stiffening of the ossicles).

Hearing aids. Amplify incoming sound (microphone, amplifier, speaker, battery; software boosts speech frequencies and suppresses noise). They make surviving hair cells respond more strongly, so they suit mild-to-moderate loss where hair cells still function.

Sound transmission through the outer or middle ear is blocked or reduced - the conducting apparatus is at fault while the cochlea still works. Causes: ear wax, otitis media (middle-ear fluid), a perforated eardrum, or otosclerosis (stiffening of the ossicles).

The cochlear hair cells or auditory nerve - the sensory/neural apparatus - are damaged. Causes: age (presbycusis), loud-noise exposure, ototoxic drugs (some antibiotics, cisplatin) and genetic conditions.

Both conductive and sensorineural components together.

For conductive loss with a non-functional outer/middle ear: a titanium skull implant conducts vibration through bone straight to the cochlea, bypassing the blocked middle ear.

For severe-to-profound sensorineural loss: the implant bypasses the dead hair cells and an electrode array directly stimulates the auditory nerve (see the diagram and worked answers). It replaces the transduction step, not the amplification step - which is why it works where a hearing aid cannot.

A small actuator vibrates the ossicles mechanically, used when conventional aids cause feedback or skin reactions.

Eye too long or cornea too curved - too much refractive power, so light focuses in front of the retina and distant objects blur. Highly prevalent and rising (almost half of young adults globally).

Eye too short or cornea too flat - too little power, so light would focus behind the retina and near objects blur.

Irregular corneal curvature focuses light at multiple points; vision is blurred or distorted.

Age-related stiffening of the lens - the eye loses its ability to accommodate for near vision. Begins around age 40 to 45. (Note: a loss of accommodation, not a resting-state refractive error.)

Opacification (clouding) of the natural lens scatters light. Common with age; also diabetes, UV exposure, steroids.

Degeneration of the central retinal photoreceptors - a leading cause of blindness in older Australians.

External refracting lenses: 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/progressive lenses correct presbyopia.