Presentation on theme: "Focussing Light onto the retina"— Presentation transcript:
1 Focussing Light onto the retina WALTHow light rays are focussed onto the retinaHow the cornea and lens refract light raysAccommodation of the eye
2 Controlling light levels Your eye are very sensitive and can be damaged by harsh light.Your iris controls light allowed into the eye by changing the size of the pupil
3 The colored part of the eye is called the iris. It controls light levels inside the eye similar to the aperture on a camera. Radial and circular muscles in the iris control pupil size in response to lightThe round opening in the center of the iris is called the pupil.
5 Focusing on objectsThe lens and cornea focus the light on the retina
6 Focusing The lens job is to make the rays hit the same point The red rays will be out of focus
7 Bending lightLight is refracted and bent to focus it as it passes through the lensLens thickness can be changed so the amount of bending is changed
8 Near vision The lens needs to bend the light more to focus it Fat lens needed
9 Distance vision Rays enter the eye closer together Need less bending Thinner lens needed
10 Changing lens thickness Ciliary muscles are attached to the lens, when relaxed they pull on the suspensory ligaments causing the lens to be thinWhen contracted the ciliary muscle cause the suspensory ligaments to slacken and so the lens is fatter
11 AccommodationWhen we open our eyes in the morning they are not focussed on near by objectsAt rest the ciliary muscles relax , puling the lens flatIn this state we can focus on distant objectsTo focus on something near by the ciliary muscles contract reducing the tension on the suspensory ligaments so the lens gets fatterThis is called accommodation – changing the shape of the lens to focus on near or distant objects
12 When the eye looks at an object that is far away the ciliary muscle relaxes which pulls on the suspensory ligaments. These pull on the lens and make it flatter (less convex). This brings the rays of light from the object into crisp focus on the retina.
14 With an object closer to the eye, the lens needs to be more convex (fatter). To do this, the ciliary muscles contract making the suspensory ligaments slack and to allow the rubbery lens to return to its naturally rounder shape.
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