Short-sightedness (myopia) occurs due to:

Short-sightedness, also known as myopia, is a common vision defect where a person can see nearby objects clearly but has difficulty seeing distant objects. The primary cause of myopia is the elongation of the eyeball, which causes light rays to focus in front of the retina instead of directly on it. This improper focusing leads to blurred vision for distant objects.

Normally, the cornea and lens of the eye bend light rays so that they converge on the retina at the back of the eye. In myopia, because the eyeball is slightly longer than normal, the focal point falls short of the retina. This is different from hypermetropia (farsightedness), where the eyeball is too short, and light focuses behind the retina.

The other options are incorrect:

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  Shifting of the iris does not affect focusing of light.

  
  


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  Weakening of the retina affects vision in other ways, such as in retinal degeneration, but is not the cause of myopia.

  
  


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  Weaker eye muscles may affect focusing temporarily (accommodation), but myopia is structural, not muscular.

  
  

Myopia can be corrected with concave lenses, which diverge light rays slightly so that they focus on the retina. Advanced treatments include laser surgery to reshape the cornea, improving vision without glasses or contact lenses.

Understanding the cause of myopia is important for optometry, biology, and everyday science, as it explains why some people need corrective lenses and how eye structure impacts vision. It also emphasizes the significance of regular eye check-ups, especially for students who spend long hours reading or using digital devices.

In summary, short-sightedness (myopia) occurs due to elongation of the eyeball, causing light to focus in front of the retina and making distant objects appear blurry.