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Physics · Glossary

What is Myopia and hyperopia?

Also known as: myopia · hyperopia · presbyopia

Definition 10.13 High School Physics · Chapter 10 — Lenses, Images, and the Eye

A myopic (short-sighted) eye is too converging for its length: parallel rays focus in front of the retina, distant objects blur, the far point is at finite distance; a diverging spectacle lens corrects it. A hyperopic (far-sighted) eye is not converging enough: near objects would focus behind the retina, the near point recedes; a converging lens corrects it. Aging stiffens the crystalline lens (presbyopia), shrinking accommodation — same remedy: reading glasses.

A myopic eye focuses parallel rays before the retina (red point); a diverging lens lands the focus on the retina. A myopic eye focuses parallel rays before the retina (red point); a diverging lens lands the focus on the retina.
A myopic eye focuses parallel rays before the retina (red point); a diverging lens lands the focus on the retina.

Examples

Example 10.14 (Prescribing for a myope)

A myopic eye has its far point at 50 cm50\,\mathrm{cm}: the correcting lens must show distant objects at the far point — object at infinity, image at OA′‾=−0.50 m\overline{OA'} = -0.50\,\mathrm{m} (virtual, in front). Then 1/f′=1/OA′‾1/f' = 1/\overline{OA'}: f′=−0.50 mf' = -0.50\,\mathrm{m}, C=−2.0C = -2.0 D; the relaxed eye looks at that virtual image and sees it sharply.

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