Meaning & use
dioptre
Last updated
Meanings
nouncountabletechnical
A unit used to measure how strongly a lens bends light, equal to one divided by its focal length in meters.
Grammar: Often follows a number: a lens of two dioptres.
Patterns
- a lens of two dioptres
Her glasses are rated at minus three dioptres.
A stronger lens has a higher number of dioptres.
The optician measured the lens at plus 1.5 dioptres.
nouncountablemedical
The strength of a person's prescription, used to describe how short- or long-sighted they are.
Grammar: Often used in the plural to give the prescription number.
Patterns
- have a prescription of something dioptres
He has six dioptres of short-sightedness in his left eye.
The surgery corrected four dioptres of vision.
Her prescription changed by half a dioptre.
Word forms
| plural | dioptres |
|---|
Common combinations
- minus two dioptres
- She wears lenses of minus two dioptres.
- plus dioptres
- Reading glasses often have plus dioptres.
- half a dioptre
- His vision worsened by half a dioptre.
- measured in dioptres
- Lens strength is measured in dioptres.
Synonyms and how they differ
- lens power
- Lens power is a general phrase for strength, while dioptre is the exact unit used to measure it.
- prescription
- Prescription means the full set of values on a prescription, not just the unit of one.
- diopter
- Diopter is the American spelling of the same word.
Word family
Commonly confused: dioptre or diopter? dioptre or diameter?
dioptre vs diopter
Diopter is the American spelling, not a different word.
dioptre vs diameter
Diameter is the width of a circle, whereas a dioptre measures lens power.
Practice
A lens that bends light more strongly will have a higher number of ____.
Choose one answer.
The dioptre measures lens power. A decibel measures sound, a kilometer measures distance, and a calorie measures energy.
Make it your own
Write a sentence using “dioptre”, then check it and compare it with the examples above.