ETIOLOGY OF MYOPIA

ETIOLOGY OF MYOPIA

Eyes are one of the important organ  of our body, it helps to see everything in our surroundings. But in present  the people are complaining that they are suffering from various type of eye problems , day by  day it is increasing rapidly. Child, young people, old all of them are suffering , most of them complain that they can not see clearly.    

Complaints coming from patients are as follows—

  1. Child is bending too much when he /she reads the book.
  2. Students can not read the letter which is written on black board.
  3. Aged person are complaining that he /she can not see the distant object clearly.
  4. Elderly people arecoften giving complain that they can not identify the face from certain distance.
  5. The image of an object looks larger and blurry.

Such type of problems you have already heard about.

All of these problems are belongs to the MYOPIA.

So now let’s discuss about myopia.At first we have to know that What is myopia ?

MYOPIA  it is a type of refractive error , for unable to see distant object.When the parallel rays are coming from infinity and after passing the cornea , crystalline lens the rays are focused in front of retina, when accommodation is rest.

Here we noticed that the parallel rays are focused  in front of retina which is the main cause of myopia.

Now discuss  why are the rays  focused in front of retina ?

  The etiological types of myopia  are——

  1. Axial myopia
  2. Curvatural myopia
  3. Positional myopia
  4. Index myopia
  5. Accommodation myopia

AXIAL MYOPIA – The anterior posterior length of the eye ball increase, then the axial length will be increase .For this reason light rays are focused in front of retina and produced myopia.

Normal axial length is 24 mm ( approx)

If the axial length become 26 mm. The axial length increase (26 -24)

2 mm , If 1mm increase of axial length produced -3D myopia. Here increases the axial length 2 mm ,  so myopia produced

(-3×2)= -6D myopia.

Changes of axial length is due to physiological variation in length of the eye ball.

CURVATURAL MYOPIA  – If the curvature of the cornea ,lens or both increase then produced myopia . 1mm increase of the curvature of cornea, lens or both produced  -6D myopia.

Example-  If the curvature increases  2 mm, then it produces (-6×2)= -12D myopia.

Curvature of the cornea is measured by an instrument called Keratometer. By the keratometry process we find out how much increase / decrease happened to the curvature of the cornea.

POSITIONAL MYOPIA– When the lens position is change anteriorly, then the total dioptric power of the eye increase , for this reason the rays are focused in front of retina , and produced myopia.

INDEX MYOPIA– Due to increase of the lens’s cortical matter then automatically refractive index changes, when the cortical matter present more in central portion it becomes opaque , so when the light rays are coming it more bends when just passes through the crystalline lens and focus in front  the retina , so it produced myopia.

In nuclear sclerosis index myopia are seen.

ACCOMMOATIONAL MYOPIA–  Some people who are not able to see near object clearly, they create force on cilliary muscle and change the power by the help of accommodative power. When it continues day by day then this person changes it’s  power in letter he / she artificially produed myopia.

We have noticed that many people in our surroundings while doing the near work squeeze  the eye, to see the near object then he / she can read some text . It is often found when they are reading the news paper .

All of the above is a type of accommodational myopia , which are produced by the excessive pressure on ciliary muscle.

Here, we represent in very short what are the causes of myopi?. What type problem seen when someone suffering for myopia? If you , your family member, friends , neighbors or others  people in your surroundings are suffering from this type problem Please consult with an eye specialist (optometrist /ophthalmologist) as soon as possible. The eye specialist will find out the factor of your problem and solve it . If you ignore it, day by day your vision become more poor , in a certain time you will realise that you lost more of your vision.

So don’t ignore if you are suffering from any type of eye problem , consult with an eye expert (Optometrist / Ophthalmologist)

SK Samiul Haque

I am an Optometrist. Primary Eye Care Professional. Proud to be an Optometrist.

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This Post Has 2 Comments

  1. Anneswa Ganguly

    Thank you so much Sir for sharing your knowledge 🙏 Really it’s much informative.

  2. Sagata Saha

    It’s very important and informative, thank you so much Sir for this all knowledge.