Everything Science Grade 11

CHAPTER 13. GEOMETRICAL OPTICS 13.3

F F’

Figure 13.15: Normal eye

Figure 13.16: Normal eye

1. short-sightedness


2. long-sightedness


3. astigmatism

Short-sightedness

Short-sightedness or myopia is a defect of vision which means that the image is focused in front of the
retina. Close objects areseen clearly but distant objects appear blurry. This condition can be corrected
by placing a diverging lens in front of the eye.The diverging lens spreads out light rays beforethey
enter the eye. The situation for short-sightednessand how to correct it isshown in Figure 13.17.

(a) Short-sightedness : Light rays are

focused in front of the retina.

(b) Short-sightedness corrected bya

diverging lens.

Figure 13.17: Short-sightedness

Long-sightedness

Long-sightedness or hyperopia is a defect of vision which means that the image is focused in behind
the retina. People with this condition can see distant objects clearly, butnot close ones. A converging
lens in front of the eye corrects long-sightednessby converging the lightrays slightly before theyenter
the eye. Reading glassesare an example of a converging lens used to correct long-sightedness.