Definition

A unit of measurement used to express the optical power of a lens or mirror, equal to the reciprocal of the focal length in meters.

Example

The optometrist measured my vision and prescribed glasses with a strength of +2.5 dioptres.

Conversation

I just got my eyes checked, and they said my prescription is 2.5 dioptre.

Oh, that sounds serious! How do you feel about it?

I guess I need glasses now, but it's not a big deal.

At least you'll be able to see clearly — that's what matters!

Synonyms & Antonyms

Root Explanation

Dioptre → It is formed from "dia-" (meaning through) and "optere" (from Greek "optēr", meaning to see). The word refers to a unit of measurement that indicates the refractive power of lenses, essentially measuring how light is seen through them.

Memory Tip

Think of 'seeing through' ('dia-' means through and 'optere' relates to seeing) to remember that a dioptre measures how well a lens can focus light.

Visually Confused Words