Defects of Human Eyes, Causes and their corrections with suitable eye lenses (Myopia, Hypermetropia and Presbyopia)Class 10 Notes.

Defects of Vision

1. Myopia (Near-Sightedness)

What is Myopia?

Myopia, also known as near-sightedness, is a condition where a person can see nearby objects clearly but cannot see distant objects clearly. This happens because the image of a distant object is formed in front of the retina.

Causes of Myopia:

• Excessive curvature of the cornea.
• Elongation of the eyeball.
• Genetic factors.
• Excessive screen time or close-up work.

Correction of Myopia:

Myopia can be corrected using a concave lens. The concave lens diverges the light rays and shifts the focus back onto the retina.

2. Hypermetropia (Far-Sightedness)

What is Hypermetropia?

Hypermetropia, also known as far-sightedness, is a condition where a person can see distant objects clearly but cannot see nearby objects clearly. This happens because the image of a nearby object is formed behind the retina.

Causes of Hypermetropia:

• Flat curvature of the cornea.
• Shortening of the eyeball.
• Genetic factors.
• Aging (presbyopia).

Correction of Hypermetropia:

Hypermetropia can be corrected using a convex lens. The convex lens converges the light rays and shifts the focus onto the retina.

3. Presbyopia

What is Presbyopia?

Presbyopia is an age-related condition where the eye loses its ability to focus on nearby objects. It occurs due to the loss of flexibility of the lens and weakening of the ciliary muscles.

Causes of Presbyopia:

• Aging (usually after 40 years).
• Loss of elasticity in the lens.
• Weakening of the ciliary muscles.

Correction of Presbyopia:

Presbyopia can be corrected using bifocal lenses. These lenses have two parts: the upper part for distant vision and the lower part for near vision.

4. Astigmatism

What is Astigmatism?

Astigmatism is a condition where the cornea or lens has an irregular curvature, causing blurred or distorted vision at all distances.

Causes of Astigmatism:

• Irregular curvature of the cornea or lens.
• Genetic factors.
• Eye injury or surgery.

Correction of Astigmatism:

Astigmatism can be corrected using cylindrical lenses. These lenses compensate for the irregular curvature of the cornea or lens.

5. Cataract

What is Cataract?

Cataract is a condition where the lens of the eye becomes cloudy, leading to blurred or dim vision. It is commonly associated with aging.

Causes of Cataract:

• Aging (most common cause).
• Diabetes.
• Prolonged exposure to UV rays.
• Smoking or alcohol consumption.

Correction of Cataract:

Cataract can be corrected through surgery. The cloudy lens is replaced with an artificial intraocular lens (IOL).