لا يختار عدسة لاصقة إلا إذا كانت وصفة النظارة جاهزة.

إلا إذا means unless.

Literally, it is made of:

• إلا = except
• إذا = if / when

So the combination gives the sense of except if → unless.

In this sentence, لا يختار ... إلا إذا ... means he does not choose ... unless ...

This لا is the ordinary negation particle used before the imperfect verb.

So:

• يختار = he chooses / he is choosing
• لا يختار = he does not choose / he does not choose

It is not the prohibitive لا used for commands such as don’t do X.
A prohibitive لا would normally be followed by a jussive verb form and would usually address you directly.

Here, the sentence is simply stating a negative fact or rule.

The subject is an implied pronoun built into the verb: هو = he.

So يختار by itself means he chooses.

In Arabic, subject pronouns are often omitted because the verb form already shows the person, number, and gender.

Depending on context, this he may be:

• a specific man
• a generic person, like one
• sometimes a translation choice where English might say you

But grammatically, the form here is definitely 3rd person masculine singular.

Because the phrase literally says a contact lens.

• عدسة = lens
• لاصقة = sticking / adhesive / contact here

Together, عدسة لاصقة means contact lens.

Arabic often uses the singular when speaking about a category or one item in general. If you wanted the plural contact lenses, you would normally say عدسات لاصقة.

So the singular here is not strange grammatically; it just means the sentence is phrased with a contact lens rather than contact lenses.

Because it is describing عدسة, and عدسة is a feminine noun.

In Arabic, adjectives agree with the nouns they describe in:

• gender
• number
• definiteness
• case

So:

• عدسة = feminine singular
• therefore لاصقة must also be feminine singular

That is why it is لاصقة, not لاصق.

This is a very common Arabic pattern.

Although كانت is formally a past-tense form of كان, after إذا Arabic often uses a past form to express a condition whose meaning is present or future in English.

So إذا كانت ... can mean:

• if it is ...
• when it is ...
• depending on context

Here, إلا إذا كانت وصفة النظارة جاهزة means unless the glasses prescription is ready.

So even though كانت looks past, the meaning in English does not have to be past.

Because the subject of كانت is وصفة, and وصفة is feminine singular.

Arabic verbs agree with their subject in gender, so:

• كان = masculine singular
• كانت = feminine singular

Since وصفة means prescription and is feminine, the sentence correctly uses كانت.

This is an iḍāfa construction, often called a genitive construction.

It means something like:

• وصفة = prescription
• النظارة = the glasses / the eyeglasses
• وصفة النظارة = the prescription of the glasses → more naturally, the glasses prescription or eyeglass prescription

In an iḍāfa:

1. the first noun does not take ال
2. the second noun is in the genitive
3. the whole phrase can still be definite if the second noun is definite

So even though وصفة has no ال, the whole phrase وصفة النظارة is definite because النظارة is definite.

Because in an iḍāfa construction, the first noun normally does not take ال.

So Arabic says:

• وصفة النظارة

not:

• الوصفة النظارة

The definiteness comes from the second noun, النظارة.
That makes the whole phrase definite: the eyeglasses prescription.

This is one of the most important patterns in Arabic noun phrases.

Because جاهزة is the predicate describing وصفة, and وصفة is feminine singular.

So the agreement is:

• وصفة = feminine singular
• جاهزة = feminine singular

If the noun were masculine, you would expect جاهز instead.

With full case endings, it would be:

لا يختارُ عدسةً لاصقةً إلا إذا كانتْ وصفةُ النظارةِ جاهزةً

Here is the breakdown:

• يختارُ: indicative ending ـُ
• عدسةً: direct object, so accusative
• لاصقةً: adjective matching عدسةً, so also accusative
• كانتْ: past tense feminine singular
• وصفةُ: subject of كانت, so nominative
• النظارةِ: second term of iḍāfa, so genitive
• جاهزةً: predicate of كان, so accusative

This is useful if you are studying formal grammar or reading fully vowelled texts.

Yes, it can.

In actual usage, words related to glasses can vary by dialect and style, and you may also see نظارات. But النظارة can be used to refer to eyeglasses.

So وصفة النظارة means the prescription for the glasses.

This is one of those cases where the English translation may use a plural noun even though Arabic uses a singular-looking form.

Yes. إذا often has a nuance of a real or expected condition, so depending on context it may be translated as:

• if
• when

In this sentence, because it follows إلا, the best English translation is usually unless:

• unless the glasses prescription is ready

But understanding that إذا often suggests a realistic condition is helpful for reading similar sentences.