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-Light rays enter through this membrane.
-Most of the refraction takes place here.
Iris- it is a dark muscular diaphragm between cornea and lens.
-it controls the size of the pupil.
- it is the color of iris that we normally perceive as eye color.
Pupil- it is a small hole between iris.
- iris regulates its opening and closing.
- during dim light it opens up due to the expansion of the iris muscles.
- during bright light it does not open up as much, in fact it only consists of a small.
Crystalline lens- it is a soft and flexible membrane like jelly which contains proteins.
-it is a convex lens,
-it perceives the image as real and inverted the image is then corrected by the brain.
Ciliary muscles- it supports or hold the lens on its place,
- it adjusts the focal length of the lens.
Retina- it consists of numerous light sensitive cells.
- these light sensitive cells get active as it receives light and produce electrical impulse and as a result the image is then passed to the brain the optical nerves,
DEFECTS OF THE HUMAN EYE
Myopia- near sight
- can see objects near them but not farther objects.
- farthest distance nearer than infinity.
- the image is formed Infront of the retina.
- correction -concave lens.
- reason - excessive curvature of the eye lens.
- elongation of the eyeball.
Hypermetropia - far sight.
- can see farther objects but not nearby objects.
- the nearest vision is further than 25cm.
- the image is formed behind the retina.
- correction- convex lens.
- reason-
Presbyopia - it mostly caused in old people.
- the near point gradually recedes away.
- reason - weakening of the ciliary muscles.
- decreasing flexibility of the eye lens.
Bi-focal lens - is used by the people who has both myopia and hypermetropia.
upper lens - concave lens - farther distances vision.
lower lens - convex lens - near distances vision.
Cataract - reason- the eye lens gets cloudy and milky.
-correction- it can be cured by cataract surgery.
- it can cause partial or complete loss of vision.
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