The human eye
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The Human Eye. 13.6 Optics. Parts of the Human Eye. Optic Nerve Transmits electrical impulses from retina to brain. Creates blind spot at the back of each eye (but compensated for by other eye). Iris Coloured part of eye

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The Human Eye

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The human eye

The Human Eye

13.6 Optics


Parts of the human eye

Parts of the Human Eye

Optic Nerve

Transmits electrical impulses from retina to brain.

Creates blind spot at the back of each eye (but compensated for by other eye)

Iris

  • Coloured part of eye

  • Opens and closes around a central hole to control the amount of light that gets in

Pupil

The hole in the iris

Cornea & Lens combination

Cornea – transparent bulge over the lens

Together, acts like a converging lens

Produces a smaller, real, inverted image on the retina

Retina

Light sensitive cells in the retina convert light signals into electrical signals


Parts of the human eye1

Parts of the Human Eye

The brain

  • Takes inverted image from the retina and flips it so that the image we “see” appears upright


Accommodation

Accommodation

  • ciliary (eye) muscles help the eye focus

  • slightly changes the shape of the eye lens


Hyperopia far sightedness

Hyperopia (far-sightedness)

Hyperopia (far-sightedness)

Can see far / can not see nearby objects

Cause:

distance between lens and retina too small, or cornea-lens combination too weak

Result:light from all nearby objects focuses behind the retina

Solution:

Far-sighted eyes need help refracting light a corrective converging lens (with a positive meniscus)


Focusing problems

Focusing Problems

Presbyopia

  • A form of far-sightedness caused by a loss accommodation as a person ages

  • Eye lens just loses its elasticity


Focusing problems1

Focusing Problems

Myopia (near-sightedness)

Can not see far / can see nearby objects

Cause:

Distance between lens and retina is too large, or cornea-lens combination converges light too strongly

Result: light from distant objects is brought to focus in front of the retina

Solution:

a corrective diverging lens (with a negative meniscus)


Focusing problems2

Focusing Problems

Astigmatism

  • abnormal curvature of the cornea (oval shape)

  • can cause two focal points to fall in two different locations

  • objects up close and at a distance appear blurry


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