Question

What are the main defects of vision and explain each of them

Answer 1

Answer:

There are mainly three common refractive defects of vision. These are

(i) myopia or near-sightedness

(ii) Hypermetropia or far – sightedness (iii) Presbyopia. Myopia is also known as near-sightedness. A person with myopia can see nearby objects clearly but cannot see distant objects distinctly.

Answer 2

The main defects of vision are :-

• Myopia (or) Short sightedness

• Hyper metropia (or) Long sightedness

• Presbyopia

• Astigmatism

• Colour blindness

Myopia :-

• A person can see nearby objects & cannot see far objects.

• Image forms before the retina.

• This defect is due to elongation of the eye ball.

• This defect can be corrected by concave lens.

• Focal length of concave lens f = -d. Where d = distance of far point.

• Focal length of eye lens becomes small.

Hypermetropia :-

• A person can see distant objects clearly, but cannot sea nearby objects.

• Image formed beyond retina.

• This defect arise due to focal length of eyelens become large.

• This defect arise due to Eyeball become to short or contract.

• This can be corrected by convex lens.

• Focal length of convex lens ${ \rm{f \: = \: \frac{25d}{d - 25} } \\ }$. Where d = distance of near point.

Presbyopia :-

• It is found in old age people.

• A person cannot see nearby objects and long objects. i.e., suffer from both myopia and hypermetropia.

• This defect arise due to weakness of ciliary muscels.

• This defect arise due to hardening of eyeball.

• This can be corrected by bi-focal lens.

• This lens consists of concave (upper portion) and convex (lower portion) lens.

Astigmatism :-

• In this defect eye cannot focus objects both in horizontal and vertical lines.

• This defect arise due to imperfect shape (not spherical) of cornea (or) lens (or) of both.

• This defect can be corrected by using cylindrical lens.

Colour blindness :-

• The person cannot distinguish between certain colours.

• This defect arises due to absence of cones with some specific colours.

• This defect cannot be curved.

• This defect can be corrected by using cylindrical lenses.

${\: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \:\: \: \: \: \:\: \:}$ $\\\\\boxed{\boxed{\begin{array}{|c|c|} \underline{\bf{Defect \: of \: Eye}} & \underline{\bf{Treatment}} \\ \\ \sf{ Myopia} & \sf{Concave \: lens} \\ \sf{Hyper \: metropia} & \sf{Convex \: lens}\\ \sf{Presbyopia} & \sf{Bifocal \: lens} \\ \sf{Astigmatism} & \sf{Cylindrical \: lens} \\ \sf{Colour \: blindness} & \sf{Cylindrical \: lens} \\ \end{array}}}$