Correcting hypermetropia
A convex lens of appropriate power.
Reading glasses
A person with hypermetropia needs the spectacles to read a book comfortably at a close distance.
What kind of lens do these spectacles have?
What this lesson covers
The idea
Hypermetropia is corrected by a convex (converging) lens of appropriate power, which provides the additional focussing power needed to form the image on the retina.
Reading glasses
A person with hypermetropia needs the spectacles to read a book comfortably at a close distance.
What kind of lens do these spectacles have?
- A convex lens
- A concave lens
- A flat sheet of plain glass
Add a lens
Slide the strength of the convex lens and watch where the image forms. The pictures are schematic, not to scale.
Extra focussing power
The hypermetropic eye cannot focus a close object on the retina by itself. A convex (converging) lens in front of the eye helps to bring the rays together sooner, so the image forms on the retina.
Hypermetropia is corrected by a convex (converging) lens of appropriate power, which provides the additional focussing power needed to form the image on the retina.
Notes
Hypermetropia is corrected by a convex (converging) lens of appropriate power, which gives the additional focussing power to form the image on the retina.
Check yourself
Which lens is used to correct hypermetropia?
What does the convex lens provide in the hypermetropic eye?
Eye-glasses with converging lenses are used for…
Which pair of lenses and defects is correct?
- A concave lens of suitable power. A concave lens is used to correct myopia.
- A triangular prism. Hypermetropia is corrected by a convex lens of appropriate power, not by a prism.
- A convex lens of appropriate power — correct. Yes!
- The additional focussing power required for forming the image on the retina — correct. Yes!
- A shorter eyeball. The lens in front of the eye does not change the eyeball. It adds focussing power.
- Less focussing power, so the image moves forward. The eye-glasses with converging lenses provide additional focussing power.
- myopia. Myopia is corrected by a concave lens, which is a diverging lens.
- hypermetropia — correct. Yes!
- a normal eye that sees distant objects clearly. Converging lenses give the additional focussing power needed in hypermetropia.
- Myopia: convex lens. Hypermetropia: concave lens. The lenses are the other way round: concave for myopia, convex for hypermetropia.
- Myopia and hypermetropia: concave lens. Hypermetropia needs a convex lens, which provides additional focussing power.
- Myopia: concave lens. Hypermetropia: convex lens — correct. Yes!