Refraction of light in the Eye

What is refraction and when does it occur?

Light refraction occurs when a light wave travels from a higher density medium to a lower density medium or vice versa.

An example of refraction is light waves travelling from air to water.

Where does refraction occur in the eye?

Refraction occurs in the eyeball where light waves are bent towards the retina to form an image. This refraction occurs with the use of refractive media. The refractive media in the eye include:

  • cornea
  • aqueous humor
  • lens
  • vitreous humor

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What is Accommodation?

Accommodation is the process by which the lens changes shape according to the distance of an object of which it is focusing on. Accommodation allows humans to focus on objects at varying distances.

How does Accomodation work?

It is possible to change the shape of the lens, and therefore altering its curvature, through the action of the ciliary body.

Accommodating Near Objects

When we focus on a close object the eye has to work harder in order to refract the light rays. Light rays at a close object are generally diverging, meaning they are splitting in an outwards direction. This causes the ciliary muscles to contract in turn causing the lens to bulge and refract the light at a higher index.

Accommodating Far Objects

If you were to look at an image one hundred meters away the ciliary body relaxes, this cause the lens to elongate, The refraction index is low. This is due to the fact that the light rays are coming in parallel lines meaning the lens needs to refract the light at a smaller angle. The effect of this process allows for a sharper image.

Summary of Accommodation

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