Explain the ways that our lens adjust its focal length according to the distance from objects?
When we look at a distant object, the ciliary muscles are in a relaxed position so as to keep the ligaments tight. Therefore the curvature of lens decreases to fix the image on retina .When we look at a near object, the ciliary muscles contract to loosen the ligaments. When ligaments relax, the curvature of lens increases naturally ,to focus the image on retina.
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Viewing
distant
objects
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Viewing
near
objects
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Ciliary
muscles
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Relaxes
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Contracts
|
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Ligaments
|
tightens
|
loosen
|
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Curvature
of lens
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Decreases
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Increases
|
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Focal
length
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Increases
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Decreases
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The characteristics of images formed on retina are Real, Small, Inverted and Accommodated.
Compare and contrast between the photo receptors seen on the retina.
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Photoreceptor
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Containing
pigment
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Function
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Related
disorder
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Rod
cells
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Rhodopsin
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Vision
under dim light
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Night
blindness
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Cone
cells
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Photopsin
/ Iodopsin
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Vision
under intense light
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Colour
blindness
|
Receptor region of the rod cells is rod shaped and contain the pigment rhodopsin, which will be stimulated under dim light. Receptor region of the cone cells is cone shaped and contain the pigment photopsin (iodopsin) which will be stimulated under intense light. Under dim light, rhodopsin dissociates to form retinal and opsin to produce impulses from rod cells. Under intense light, photopsin (iodopsin) dissociates to form retinal and opsin to produce impulses from cone cells. The three types of cone cells (red, green & blue) provide us with colour vision.
Vitamin A help us for better vision because Retinal, the visual pigment found in the photoreceptors, is formed from vitamin A.
Blind spot VS Yellow spot
Blind spot is a part of retina from where the optic nerve begins. No photoreceptors at this spot, hence
no vision.
Yellow spot is the point of highest vision in the retina, where more cone cells seen. Images
form in and around the yellow spot.
Point on retina lacking vision is the Blind spot.
Point of highest vision in retina Yellow spot.
The bird, owl has no vision in day time because Owl’s retina is devoid of cone cells and hence no vision in day time. Animals like cat and owl have more vision at night because Cat and owl has more rod cells in their retina, so that they have more vision at night.
A kite can locate its prey even from high altitude because the eyes of kite are closer to each other and contain a large number of cone cells. Hence it has high power of vision
What are the changes occur in retina when images focus on it ?
When light rays from the object passes through cornea and pupil fall on the lens, a small, real inverted image forms on the retina. When the image is formed under dim light, rhodopsin in the rod cells dissociate to produce impulses and when the image is formed under intense light, photopsin in the cone cells dissociate to produce impulses. These impulses are transmitted through the optic nerve. The brain coordinates the images from both eyes to feel perfect vision
Though images of object are formed in both eyes, we can see only one object. The reason behind this is Cerebrum coordinates the two images and hence get a three dimensional view of the object
Binocular vision : The ability of both the eyes to focus on the same object is known as binocular vision. Binocular vision help us to get a three dimensional image of the object. This help us to calculate the correct distance, depth, height and width of the object.
The Reason of closing one eye while shooting an object : Binocular vision help us to get a three dimensional image of the object and to calculate the correct distance, depth, height and width of the object. But in the case of aiming an object, we need to get correct line instead of common focus through binocular vision.
