Defects of vision
Three common refractive defects.
Blurred words
A student cannot read the blackboard clearly, or another person cannot read a newspaper without holding it far away. Their eyes are not working as well as before.
What can often be done to fix this kind of problem?
What this lesson covers
The idea
When the eye loses its power of accommodation, vision becomes blurred; the three common refractive defects are myopia, hypermetropia and presbyopia, and they can be corrected with suitable spherical lenses.
Blurred words
A student cannot read the blackboard clearly, or another person cannot read a newspaper without holding it far away. Their eyes are not working as well as before.
What can often be done to fix this kind of problem?
- Use suitable spherical lenses in spectacles
- Wear a thicker coat
- Read in the dark
Defects and cures
Open every tab.
Three common defects
When the eye loses its power of accommodation, vision becomes blurred. Three common defects are myopia, hypermetropia and presbyopia. Spectacles with the right lenses can correct them.
When the eye loses its power of accommodation, vision becomes blurred. The three common refractive defects are myopia, hypermetropia and presbyopia, and they can be corrected with suitable spherical lenses.
Notes
When the eye loses its power of accommodation, vision is blurred. Myopia, hypermetropia and presbyopia are the three common refractive defects, corrected by suitable spherical lenses.
Check yourself
When the eye loses its power of accommodation, vision becomes…
How many common refractive defects of vision does the chapter name?
Answer: 3
Myopia, hypermetropia and presbyopia are the three common refractive defects.
Which of these is one of the three common refractive defects?
Refractive defects of vision can be corrected by using…
- brighter. Losing accommodation means the person cannot see objects distinctly and comfortably, so vision becomes blurred.
- unchanged. The vision becomes blurred when the eye loses its power of accommodation.
- blurred — correct. Yes!
- Presbyopia — correct. Yes!
- Cataract. Cataract is the milky and cloudy crystalline lens in old age. The three common refractive defects are myopia, hypermetropia and presbyopia.
- Dispersion. Dispersion is the splitting of light into its component colours. It is not a defect of vision.
- a triangular prism. These defects are corrected by suitable spherical lenses.
- suitable spherical lenses — correct. Yes!
- a plane mirror. These defects are corrected by suitable spherical lenses.