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Tamil Nadu Board of Secondary EducationSSLC (English Medium) Class 10
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Defects of Vision and Their Corrections > Myopia

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Maharashtra State Board: Class 10

Myopia and Its Causes

Myopia, also known as nearsightedness, is a common refractive error where distant objects appear blurry, while nearby objects are seen clearly.  This occurs when light rays converge in front of the retina instead of focusing directly on it. It is also referred to as a refractive error because the eye cannot bend light properly.

Nearsightedness

Myopia is mainly caused by structural defects in the eye that affect light focusing.

Structural Causes:

  1. Excessively curved cornea or lens → Increases the converging power of the eye lens.
  2. Elongated eyeball → Increases the distance between the lens and retina, causing premature light convergence.

Due to these structural abnormalities, images of distant objects form in front of the retina, leading to blurred vision.

Maharashtra State Board: Class 10

Types and Symptoms of Myopia

  1. Simple Myopia: A mild form of myopia, correctable with glasses or contact lenses.
  2. High Myopia: A severe form that progresses with age, increasing the risk of cataract, glaucoma, and retinal detachment.
  3. Pathological (Degenerative) Myopia: A rare and severe form that can lead to permanent vision loss and cannot be corrected with lenses.

Symptoms of Myopia:

  • Blurred vision when looking at distant objects (e.g., road signs, classroom boards).
  • Squinting or partially closing eyelids to see clearly.
  • Eyestrain and fatigue while performing activities like driving or playing sports.
  • Frequent headaches due to prolonged focus strain.
Maharashtra State Board: Class 10

Myopia Correction and Treatment

Myopia Correction Methods:

A. Spectacles and Contact Lenses

Concave lenses (negative power lenses) are used to diverge incoming light rays, allowing the eye’s lens to focus the image directly on the retina. Eyeglasses and contact lenses are the most common correction methods.

B. Orthokeratology (Ortho-K)

A non-surgical treatment where a person wears rigid contact lenses overnight to temporarily reshape the cornea.  It is used for mild cases of myopia.

C. Surgical Treatments for Myopia

  • Laser Surgery (LASIK, PRK, SMILE): It uses laser technology to reshape the cornea, correcting the light focus.
  • Lens Implant Surgery: Involves inserting a corrective artificial lens inside the eye for permanent correction.
CBSE: Class 10
Maharashtra State Board: Class 10

Key Points: Myopia

  • Myopia is a vision defect in which distant objects appear blurry, while near objects are seen clearly.
  • This occurs because the image of distant objects forms on the retina.
  • The far point is not at infinity but is shifted closer to the eye.
  • Causes include increased curvature of the cornea/lens or elongation of the eyeball.
  • Corrected using a concave lens of negative power, which diverges light rays to focus the image on the retina.

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Related QuestionsVIEW ALL [167]

The picture given here shows a person wearing ‘half-moon’ spectacles. What sort of eye-defect do you think he has? Why are these particular spectacles useful to him?

Explain the terms ‘adaptation’ and ‘accommodation’ with reference to the eye.

A student suffering from myopia is not able to see distinctly the objects placed beyond 5 m. List two possible reasons due to which this defect of vision may have arisen. With the help of ray diagrams, explain

(i) why the student is unable to see distinctly the objects placed beyond 5 m from his eyes.

(ii) the type  of the corrective lens used to restore proper vision and how this defect is corrected by the use of this lens.

(b) If, in this case, the numerical value of the focal length of the corrective lens is 5 m, find the power of the lens as per the new Cartesian sign convention

A person cannot read newspaper placed nearer than 50 cm from his eyes. Name the defect of vision he is suffering from. Draw a ray diagram to illustrate this defect. List its two possible causes. Draw a ray diagram to show how this defect may be corrected using a lens of appropriate focal length.

The diagram alongside represents a section of a mammalian eye.
(i) Label the parts 1 to 5 of the diagram.
(ii) State the function of the parts labelled 4 and 5.
(iii) With the help of a diagram show the short sightedness.

A student is unable to see clearly the words written on the blackboard placed at a distance of approximately 4 m from him. Name the defect of vision the boy is suffering from. Explain the method of correcting this defect.

Draw ray diagram for the:-

(i) defect of vision and also

(ii) for its correction.

State one role of ciliary muscles in the human eye.

Choose the correct answer : 
Presbyopia is a disease of _____________

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