Chapter 10 · Question 3

Differentiate between myopia and hypermetropia based on their causes and the type of corrective lenses used.

Answer Revealed

Direct Answer:

Myopia (near-sightedness): distant objects appear indistinct because the image forms in front of the retina; corrected with a concave lens. Hypermetropia (far-sightedness): nearby objects appear indistinct because the image forms behind the retina; corrected with a convex lens.

Simple Explanation

If you have myopia, you can see close objects clearly but distant things look blurry — the eye focuses the image too early, in front of the retina. A concave (diverging) lens fixes this. With hypermetropia, close objects are blurry but far ones are clear — the image focuses behind the retina. A convex (converging) lens fixes this.

Exam-Ready Structure

Myopia and hypermetropia are two common refractive vision defects with distinct causes and corrections: Myopia (near-sightedness): 1. Cause — The eye lens is too converging, or the eyeball is too elongated, causing the image of a distant object to form in front of the retina instead of directly on it. 2. Effect — The person can see nearby objects clearly but cannot see distant objects distinctly. 3. Far point — The far point of a myopic eye is closer than infinity. 4. Correction — A concave (diverging) lens of suitable power is placed in front of the eye. The concave lens diverges the incoming rays so that they appear to come from the far point of the defective eye, after which the eye lens focuses them on the retina. Hypermetropia (far-sightedness): 1. Cause — The eye lens is too weak (less converging), or the eyeball is too short, causing the image of a nearby object to form behind the retina. 2. Effect — The person can see distant objects clearly but cannot see nearby objects distinctly. 3. Near point — The near point of a hypermetropic eye is farther than 25 cm. 4. Correction — A convex (converging) lens of suitable power is placed in front of the eye. The convex lens converges the incoming rays so that they appear to come from the normal near point (25 cm), after which the eye lens focuses them on the retina.

Key Points

Myopia: image forms in front of retina; corrected by concave lens
Myopia: cannot see distant objects clearly
Hypermetropia: image forms behind retina; corrected by convex lens
Hypermetropia: cannot see nearby objects clearly
Both corrected using lenses of suitable power

Common Mistakes

Mixing up which defect uses which lens (concave for myopia, convex for hypermetropia)
Saying myopic people cannot see near objects (they can see near objects clearly)

Differentiate between myopia and hypermetropia based on their causes and the type of corrective lenses used.