Biology
Aman's father, aged 50 years, is suffering from an eye defect. He can see the distant objects clearly but not the nearby ones. He keeps the newspaper and books far away from his eyes to read. Answer the following questions :
(a) Identify the eye defect.
(b) Mention the possible reason for this defect.
(c) What kind of lens can be used to correct this defect?
(d) Name the structure in the human eye which holds the lens in proper position and attaches it to the ciliary body.
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Answer
(a) Presbyopia
(b) The possible reason for this defect is that the lens loses flexibility resulting in a kind of far-sightedness.
(c) Convex lens is used to correct this defect.
(d) The structure in the human eye which holds the lens in proper position and attaches it to the ciliary body is suspensory ligaments.
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The eye is sensitive to light and is responsible for vision. The main parts of an eye are sclera, cornea, retina and lens. Lens passes the light rays to the retina through vitreous humour. Retina is the sensitive layer of the eye which contains sensory cells for image formation. The impulses of the image are then carried from retina to the brain through optic nerves.
(i) Lens is filled in front of the eye ball between aqueous humour and vitreous humour, which has the following characteristic features :
- Biconvex, translucent and richly supplied with blood vessels.
- Oval shaped, transparent and elastic in nature.
- Biconvex, flexible and non-vascular.
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(ii) The sensory cells of the eye - rods and cones are located on the retina and help in image formation. If cones of a person are damaged or diminished in number, what will be its effect ?
- Person will be able to see better in bright light.
- Person will be able to see better in dim light.
- Person will be unable to distinguish between different colours.
- Both 2 and 3