Brillestyrken måles i dioptrier.

Because Norwegian usually forms noun + noun combinations as compound words.

• brille = glasses / spectacles
• styrke = strength, power

So brillestyrke means something like glasses power or lens strength. Then brillestyrken is the definite singular form: the glasses power / the prescription strength.

This is very normal in Norwegian. English often uses separate words where Norwegian prefers one compound.

The ending -en marks the noun as definite singular.

The base noun is:

• en brillestyrke = a glasses strength / a prescription strength

The definite form is:

• brillestyrken = the glasses strength / the prescription strength

In Norwegian, the definite article is often attached to the end of the noun instead of being a separate word like the in English.

In Norwegian compounds, the first noun is often in its base form, not necessarily the form that would sound most natural in English.

So:

• brille = glasses / spectacle
• brillestyrke = glasses strength

Even though English uses the plural word glasses, Norwegian commonly uses brille- in compounds. This is just how Norwegian builds many compound nouns.

Måles is the present tense s-passive form of å måle = to measure.

So:

• måler = measures / is measuring
• måles = is measured / are measured

In this sentence, måles means is measured.

This -s passive is very common in Norwegian, especially in factual or general statements like scientific, technical, or formal language.

Yes. That is also correct.

• Brillestyrken måles i dioptrier
• Brillestyrken blir målt i dioptrier

Both mean roughly the same thing: The lens power is measured in diopters.

The difference is mostly stylistic:

• måles sounds more compact and general
• blir målt is a more explicit passive construction

In definitions, facts, and textbook-style statements, the -s passive is very common.

Here i means in, as in measured in diopters.

Norwegian often uses i with units of measurement:

• måles i meter = is measured in meters
• måles i kilo = is measured in kilos
• måles i grader = is measured in degrees

So i dioptrier is the natural way to say in diopters.

Because Norwegian usually uses a bare plural noun after expressions of measurement units.

So you say:

• i dioptrier = in diopters
• i meter = in meters
• i liter = in liters

You normally do not add an article here. It works much like English in phrases such as measured in meters.

The noun is:

• en dioptri = a diopter
• dioptrien = the diopter
• dioptrier = diopters
• dioptriene = the diopters

So in the sentence, dioptrier is the indefinite plural form.

Yes. The sentence structure is:

• Brillestyrken = subject
• måles = verb
• i dioptrier = prepositional phrase telling you the unit

So the sentence follows normal Norwegian main-clause word order: subject + verb + rest.

It is a general statement.

The present tense in Norwegian is often used for facts, definitions, and general truths. So måles here does not mean someone is measuring it right this second. It means this is the standard way lens power is expressed.

In other words, the sentence means something like:

• Lens power is measured in diopters
• Diopters are the unit used to express lens power

Sometimes, depending on context, yes — but not perfectly.

More literally, brillestyrke refers to the optical power of the lenses. In everyday English, that may overlap with prescription strength or simply prescription, but prescription can also include more information than just the diopter value.

So the most precise understanding is:

• brillestyrke = lens strength / glasses power / prescription strength

Not always the entire prescription in every technical sense.