The Eye and the Ear – Accommodation, Defects and Hearing
BiologyHuman & Animal PhysiologyAges 16–17
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Sign in to playA ray model of the eye: move the object near or far and watch the ciliary muscle, suspensory ligaments and lens accommodate, then choose myopia, hyperopia, presbyopia or astigmatism and correct it with a spectacle lens of power P = 1/f. Three more screens show the pupil reflex responding to light, the density and sensitivity of rods and cones, and the path of sound to the cochlea with hearing aids and cochlear implants.
Lesson: Eye structure, accommodation, sight defects and their correction, the pupil reflex, rods and cones, the ear and hearing technologies
What it shows
The eye focuses light mainly at the cornea and fine-tunes with the lens. For a near object the ciliary muscle contracts, the suspensory ligaments slacken and the lens becomes fatter, so its power increases; for a distant object the muscle relaxes and the ligaments pull the lens thin. In myopia the eyeball is too long, so a diverging lens is needed; in hyperopia it is too short, so a converging lens is needed. Lens power P = 1/f is measured in dioptres. The other screens model the pupil reflex arc, rods and cones in the retina, and how the cochlea, hearing aids and cochlear implants turn sound into nerve impulses.
How to use
On Eye & lenses, drag Object distance from far to near and read how the eye power and ciliary muscle change. Choose a defect in Eye defect, note the near and far points, then move Spectacle lens until the image is sharp again. On Pupil reflex, use Light or the Dark room and Sunlight buttons and follow the reflex arc. On Rods & cones, change Light and Wavelength. On Ear & hearing, set Hearing loss and Device, then press Play tone.
Parameters you can change
- Screen Eye & lenses, Pupil reflex, Rods & cones, Ear & hearing
- Object distance from the eye 10–1000 cm
- Eye defect Normal eye, Myopia (short sight), Hyperopia (long sight), Presbyopia, Astigmatism
- Spectacle lens power -6–6 D
- Light intensity (log scale, 0 = 0.01 lx, 100 = 100,000 lx) 0–100 %
- Wavelength of light 400–700 nm
- Sound frequency 20–20000 Hz
- Sound level 0–120 dB
- Hearing loss None, Conductive (middle ear), Sensorineural (hair cells), Profound deafness
- Hearing device None, Hearing aid, Cochlear implant
- Show part labels
Questions to explore
- Why does a short-sighted eye with a far point of 50 cm need a lens of −2 D?
- How do the ciliary muscle and suspensory ligaments change when you look from a distant tree to a book?
- Why can a cochlear implant help profound deafness when a hearing aid cannot?
