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THE EYE OF THE HUMAN

  • the human eye is the sense organ in the body to see and identify the objects.
  • the cornea is a layer of the eye that protects eye from the dust and it acts as a protective membrane.
  • behind the cornea, a humorous liquid is filled in a space.
  • the iris contains a pupil in it, iris allows the light to pupil.iris is a muscular diaphragm.
  • the pupil is a hole.it catches the light and does not reflect back.it is in black color.
  • the lens is the backward covered portion to form the image from the retina.

NOTE 1:
the distance between the lens and retina is about 2.5 cm.

due to the deficiency of vitamin A in our body, these symptoms may cause to eye:
 night blindness, cornea failure.

the retina contains the 125 million receptors called rods and cones which receives the light signal data from the eye and sends it to the brain through 1 million optic nerves.
 
NOTE 2:
the lenses are; concave,convex,bi concave,bi convex,plano concave,plano convex, concavo-convex.

HUMAN EYE SIGHTS:

there are many common defects of the human eye;

  • Near sight: the objects near the eye can see but the objects far from the eye can't see called MYOPIA or NEAR SIGHT.
          the above defect can be eliminated by using the biconcave lens.

  • Long sight: the objects near the eye can't see but the objects far from the eye can see called HYPER MYOPIA or LONG SIGHT.
   the above defect can be eliminated by using the biconvex lens.

  • PRESBYOPIA: this type of problem occurs by ageing.
this can be rectified by using the bifocal lens means using both the convex and concave lens.
the bifocal lens of the upper portion consists of a concave and the lower portion consists of a convex lens.

NOTE 3: the different types of lenses




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