i) Short sight (Myopia)
-eye cannot focus on far objects.
-image is formed in front of the retina because light rays converge in front of retina.
-the lens is too thick, curve and eyeball too long.
-corrected by wearing concave/biconcave/lenses
-these lenses diverge light rays onto retina.
ii) Long sight (Hypermetropia)
-eye lenses are unable to focus because they are flat, thin and weak hence unable to focus image on the retina.
-they are unable to accommodate/change the focal length.
-near image is formed behind the retina but a distant one is correctly focused on the retina.
-corrected by wearing convex/biconvex/converging lenses.
iii) Presbyopia
-occurs in old age hence called old sight
caused due to loss of elasticity of lenses, weakness of ciliary muscles hence lack of focus of light rays.
-this causes long sight
-corrected by wearing biconvex/convex/converging lenses
iv) Squinting
-eyeballs are uncoordinated/do not turn at the same time.
-eye muscles move in different directions
this makes accommodation and focusing difficult.
-corrected through surgery.
v) Astigmatism
-surface of cornea is uneven.
-leads to weak focus of light raise on retina.
-corrected by using cylindrical lenses/lenses with combined curvature.
Anganifelix answered the question on April 18, 2018 at 11:33
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