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A short sightedness person can see nearby
objects clearly but distant object appear blur
It occurs because the image of a distant
objects falls in front of the retina The defects may be caused
Abnormally long eyeballs
Eye lens that are abnormally thick
The defects can be corrected by wearing
concave lenses (diverging lenses)
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A long-sightedness person can see distant
objects clearly but nearby object appear blur
It occurs because the image of a nearby
objects falls behind the retina The defects may be caused
Abnormally short eyeballs
Eye lens that are abnormally thin
The defects can be corrected by wearing
convex lenses (converging lenses)
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Is caused by the irregular curvature of
the retina
All the light rays of an object do not meet
at a point on the retina.
S
ome light rays are focused on theretina
Others are focused either in front or
behind the retina
In many cases, astigmatism causesblurred vision for either near or distant
objects.
The defects may be corrected by
wearing cylindrical lenses
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OP IC L
ILLUSIONBLIND SPO
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Sometimes what we see may not appear to
be the real thing. This is because the brain
cannot interpret accurately what is actually
seen by eyeOptical illusion is the limitation of the sense
of sight
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Refer page __ in your text book
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Blind spot is a point on the retina of the eye
that cannot detect any images
The blind spot does not have any nerve
receptors sensitive to light It is found at the beginning of the optic
nerve
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Is the vision involving both eyes
The brain will combine the vision from both
eyes to form 3-dimensional image
Each eye sees a slightly different image
This enable us to estimate distancesaccurately
The stereoscopic field of vision is narrow
Predators usually have stereoscopic vision
Example: tiger, owl, lion, cat, human
Refer page_ text book
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Is the vision involving one eye only
Makes estimation distances accuratelydifficult
Produces a flat image
The monocular field of vision is wide
Preys usually have monocular vision
Detect their enemies from a wide range of
directions
Example: rabbit, chicken, deer
Refer page_ text book
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Optical instruments can be used to help
overcome the limitations of the sense of
sight.
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What is this??
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TE ES OPE AND BINO AR
- Help us to see distantobjects
MI ROS OPE
-helps us to see fineand small objects
X RAY MA HINE-enable us to observeour bodies· internal
organs
PERIS OPE-used in submarines tosee above the sea level
