המרחק בין האישונים כתוב במרשם למשקפיים.

מרחק means distance.

The prefix ה־ is the definite article, equivalent to the in English. So המרחק means the distance.

In this sentence, Hebrew is talking about a specific measurement, so the distance is natural.

• מרחק = distance
• המרחק = the distance

האישונים means the pupils, as in the pupils of the eyes.

The singular is אישון = pupil.

So:

• אישון = pupil
• אישונים = pupils
• האישונים = the pupils

A learner may notice that אישון looks related to איש. Historically it is, but in modern Hebrew אישון is simply the normal word for the pupil of the eye.

בין means between.

So בין האישונים means between the pupils.

This is the normal way to express this idea in Hebrew. Since the sentence is talking about the distance from one pupil to the other, Hebrew uses between just as English does.

Breakdown:

• בין = between
• האישונים = the pupils
• בין האישונים = between the pupils

Because it agrees with המרחק, which is a masculine singular noun.

In this sentence, כתוב means written and functions like a predicate adjective or participle. Hebrew adjectives and participles usually agree in gender and number with the noun they describe.

Since:

• המרחק is masculine singular

we get:

• כתוב = masculine singular

If the subject were feminine singular, you would expect כתובה.
If it were masculine plural, you would expect כתובים.

In present-tense sentences, Hebrew usually does not use a separate word for is / are.

So:

• המרחק ... כתוב
  literally looks like
• the distance ... written

but it means:

• the distance ... is written

This is completely normal in Hebrew.

So the structure is:

• המרחק בין האישונים = the distance between the pupils
• כתוב = written
• together: The distance between the pupils is written ...

Both are related to writing, but they are not used in exactly the same way.

• כתוב = written, appears written, is stated
• נכתב = was written / got written

In this sentence, כתוב is more natural because the focus is on the fact that the information appears in the prescription or is listed there, not on the action of someone writing it.

So כתוב fits English is written very well here.

ב־ usually means in, at, or sometimes on, depending on context.

מרשם means prescription.

So במרשם means something like:

• in the prescription
• on the prescription

In English, on the prescription may sound more natural in some contexts, but Hebrew commonly uses ב־ for this kind of idea.

Also, in unpointed Hebrew, במרשם can represent either:

• in a prescription
• in the prescription

The exact meaning depends on context.

Here ל־ means for.

So:

• מרשם למשקפיים = a prescription for glasses

This is very natural Hebrew.

Breakdown:

• מרשם = prescription
• ל־ = for
• משקפיים = glasses
• מרשם למשקפיים = prescription for glasses

So the full phrase means that the pupil distance is written in the glasses prescription.

Yes, משקפיים is a plural-looking noun, and historically it has the dual ending ־יים.

The dual often appears in words for things that come in pairs, and glasses are a good example.

In modern Hebrew, משקפיים is treated as a normal fixed word meaning glasses. There is no common everyday singular form meaning one glass of the pair.

So for a learner, the important thing is simply:

• משקפיים = glasses

Yes, this sentence is natural.

A very common shorter expression is also:

• מרחק אישונים = pupillary distance

So in real life, people might talk about:

• מרחק אישונים
• המרחק בין האישונים

Both are understandable, and the second one is very transparent for learners because it literally says the distance between the pupils.

Hebrew often uses the definite article when the speaker means a specific, understood thing.

Here:

• המרחק = the specific measurement being discussed
• האישונים = the pupils of the person’s eyes, which are also specific

So the sentence is not talking about a random distance between some pupils somewhere. It is talking about a known measurement in a particular context, namely an eyeglasses prescription.

That is why the definite forms sound natural here.

The structure is:

• המרחק בין האישונים = subject
• כתוב = predicate adjective/participle
• במרשם למשקפיים = prepositional phrase giving location/context

So literally, the sentence is arranged like this:

• The distance between the pupils
  • written
    • in the eyeglasses prescription

A more natural English translation adds the present-tense is:

• The distance between the pupils is written in the eyeglasses prescription.