Correcting myopia
A concave lens of suitable power.
Glasses for the blackboard
A student who is short-sighted wears spectacles and then reads the blackboard. Without the spectacles the board is blurred.
What kind of lens do the spectacles have?
What this lesson covers
The idea
Myopia is corrected by a concave lens of suitable power, which brings the image of a distant object back on to the retina.
Glasses for the blackboard
A student who is short-sighted wears spectacles and then reads the blackboard. Without the spectacles the board is blurred.
What kind of lens do the spectacles have?
- A concave lens
- A convex lens
- A flat sheet of plain glass
Add a lens
Slide the strength of the concave lens and watch where the image forms. The pictures are schematic, not to scale.
Back on the retina
The myopic eye forms the image of a distant object in front of the retina. A concave lens spreads the rays a little before they enter the eye, so the eye brings them to a point further back, on the retina.
Myopia is corrected by a concave lens of suitable power, which brings the image of a distant object back on to the retina.
Notes
Myopia is corrected by a concave lens of suitable power, which brings the image of a distant object back on to the retina.
Check yourself
Which lens is used to correct myopia?
What does the concave lens do for a myopic eye?
In the picture, the concave lens is made much stronger than the suitable one. Where does the image go?
- A convex lens of suitable power. A convex lens is used to correct hypermetropia.
- A concave lens of suitable power — correct. Yes!
- A triangular prism. Myopia is corrected by a concave lens of suitable power, not by a prism.
- It makes the eyeball shorter. The lens is placed in front of the eye and does not change the eyeball. It brings the image back on to the retina.
- It makes the image form even farther in front of the retina. The concave lens of suitable power brings the image back on to the retina.
- It brings the image of a distant object back on to the retina — correct. Yes!
- It moves behind the retina — correct. Yes!
- It stays in front of the retina. A stronger concave lens moves the image farther back, so with too much strength it goes behind the retina.
- It stays exactly on the retina. Only a lens of suitable power puts the image on the retina.