Defects of Eye and their Correction
Human beings have two eyes situated in deep sockets or on the front side of the head. Human eyes are photoreceptors (respond to light).
Short-Sightedness or Myopia
in this condition, light is focused in front of the retina, and a blurred image is formed in front of the retina. in myopia comedy near objects are seen clearly while the distant objects appear blurred. This happens because either the eyeball is elongated or the lens has become too thin or curved.
Myopia can be corrected by using a concave (diverging) lens.
Long Sightedness or Hypermetropia
in this condition, the light is focused behind the retina, As a result, the distant objects are seen clearly, while the near objects appear blurred. long-sightedness results due to the shortening of the eyeball or the lens have become too thin.
Hypermetropia can be corrected by using a convex (converging) lens.
Astigmatism
this is a more complicated defect in a vision for a start in this comic the surface of the cornea becomes irregular and therefore some of the light rays are focused while others are not. As a result, some parts of the object appear blurred while the other parts appear clear.
Astigmatism can be corrected by using a cylindrical lens that bent light rays in one direction only.
Presbyopia
In this condition, the lens loses its flexibility and as a result, the near objects cannot be seen clearly. This defect normally occurs in older people. Presbyopia can be corrected by using a convex lens.
Night Blindness
In this condition, there is a difficulty in seeing in the dim light. This is because of the non-production of rhodopsin pigment in the rod cells, which functions and dim light. In the absence of rhodopsin, these cells cannot function. Thus, there is a lack of normal night vision. It is most often caused due to the deficiency of vitamin A. Night blindness can be cured by having vitamin A rich diet.
Colour Blindness
in this condition, a person is unable to discriminate between red and green colours. This is a genetic defect. It is an X linked disease. Colour blindness cannot be treated during the lifetime of an individual.
Cataract
In this condition comma, the lens of the eye becomes opaque and as a result, the vision is cut down. cataract can be treated by surgical removal of the lens and using a convex lens in the spectacles which compensate for the removed lens. Nowadays, a small plastic lens is implanted behind iris to correct the defect.
Squint
in this condition, either the two eyes somewhat convert a diverse. In both these conditions, a person may have double vision. Squint in the eyes can be treated by surgery or by suitable exercises.
