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When referring to the eye, what is accommodation?

Accommodation is the reflex that changes the refractive power of the lens to allow us to focus on nearby or distant objects.

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Which two structures refract (bend) light entering the eye? 

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When trying to focus on a nearby object, does the eye need to refract the light strongly or weakly?

The light will need to be refracted strongly when focusing on nearby objects.

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What shape should the eye's lens be to refract light most strongly?

When the eye's lens is short and fat (more rounded) it refracts light more strongly.

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What happens to the ciliary muscle and suspensory ligaments to make the lens short and fat?

1The ciliary muscle will contract.


2The suspensory ligaments will slacken (become loose).

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Explain the changes that take place in the eye when it focuses on a distant object.

When the object is far away light will only need to be refracted weakly, so the lens needs to be long and thin.


To make the lens long and thin, the ciliary muscle will relax and the suspensory ligaments will be pulled taut, stretching out the lens. 

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What does 'long-sighted' mean?

The eye is unable to focus on nearby objects.


Another way to think about it is that long-sighted means that you can focus well over long distances (but can't focus over short distances so well). 

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What term is used when somebody is unable to focus on distant objects?

Short-sighted.

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Which type of lenses would glasses need to contain in order to correct short-sightedness? Explain why.

Concave lenses. The problem with short-sightedness is that the lens of the eye is too short and fat, so refracts light too strongly.


A concave lens in the glasses would refract light outwards in order to counteract the over-refraction of the eye's lens.

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