لا يقرأ لوحة فحص النظر إلا إذا ركز جيدا.

لا is the normal way to negate the imperfect verb in a simple present or general statement.

So:

• يقرأ = he reads / he is reading
• لا يقرأ = he does not read / he cannot read in context

Here it gives a general idea such as he does not read the eye chart unless... rather than a command or a past event.

يقرأ is an imperfect verb. In Arabic, the imperfect can cover several ideas that English separates:

• present: he reads / he is reading
• habitual: he reads
• general truth: he reads
• sometimes future, depending on context

In this sentence, it most naturally expresses a general condition or repeated situation, not a one-time event. That is why there is no need for a future marker like سـ or سوف.

The subject is built into the verb.

• يقرأ means he reads
• ركز means he concentrated / he focuses depending on context

Arabic often leaves the subject pronoun unstated when it is already clear from the verb form. So the sentence has an understood subject: هو = he.

This is an iḍāfa construction, often called a possessive or noun-linking construction.

Here the phrase is:

• لوحة = chart / board
• فحص النظر = eye test / vision test

Together:

• لوحة فحص النظر = the eye-test chart / chart of the vision test

In an iḍāfa:

1. the first noun does not take ال
2. the first noun does not take tanwīn
3. the following noun is in the genitive relationship

So لوحة cannot become اللوحة here if it is directly linked to فحص النظر.

It is another iḍāfa inside the larger phrase.

• فحص = examination / test
• النظر = sight / vision

So:

• فحص النظر = test of vision, that is, eye test

Then that whole phrase attaches to لوحة:

• لوحة فحص النظر = chart of the eye test

So the sentence contains a nested structure:

• لوحة
  • فحص
    • النظر

Literally, it is something like:

• chart [of test [of vision]]

This kind of chaining is very common in Arabic.

With a negative main clause, إلا إذا means something like:

• except if
• unless
• only if

So:

• لا يقرأ ... إلا إذا ركز جيدا = He does not read ... unless he concentrates well = He only reads ... if he concentrates well

This is a very common pattern in Arabic: a negative statement followed by إلا إذا to give the one condition under which it becomes true.

This is a very common point of confusion for English speakers.

After إذا, Arabic often uses a past-form verb even when the meaning is present or future in English.

So:

• إذا ركز literally looks like if he concentrated
• but in actual meaning it can be if/when he concentrates

This is normal formal Arabic usage. The past form after إذا does not necessarily mean past time.

Also, ركز is Form II of the root related to focusing/concentrating, so ركّز means to concentrate / focus.

جيدا means well.

So:

• ركز جيدا = he concentrated well / he focused well

Grammatically, Arabic often uses an accusative form to express adverb-like meanings. In fully vocalized Arabic, this is usually written:

• جيدًا

So even though جيد is basically an adjective meaning good, the form جيدًا works like the adverb well in this sentence.

In everyday Arabic writing, short vowels and most case endings are usually omitted.

So you see:

• لا يقرأ لوحة فحص النظر إلا إذا ركز جيدا

But if fully vocalized in careful MSA, it would be:

• لا يقرأُ لوحةَ فحصِ النظرِ إلا إذا ركّزَ جيدًا

Those endings show grammar:

• يقرأُ: indicative ending
• لوحةَ: direct object, so accusative
• فحصِ: genitive because of iḍāfa
• النظرِ: also genitive
• ركّزَ: past verb
• جيدًا: accusative adverbial form

The tricky part is the hamza at the end of the root.

يقرأ is pronounced roughly:

• yaqraʾu in full classical/MSA pronunciation

The important thing is that the final ء is a real consonant, a glottal stop. So it is not pronounced like one smooth syllable at the end.

A helpful breakdown is:

• yaq-ra-ʾu

Not:

• yaqru
• yaqraa

The root is ق ر أ, the same root used in قراءة (reading) and القرآن.

Most naturally, it sounds like a general rule or repeated situation.

Something like:

• He does not read the eye chart unless he really focuses
• He can only read the eye chart if he concentrates well

That comes from the combination of:

• the imperfect verb يقرأ
• the negative لا
• the conditional expression إلا إذا

So the sentence feels less like a one-time story event and more like a general statement about ability or performance.

Yes, but إذا fits well here.

Very roughly:

• إذا often suits general or expected situations: if/when
• إن can sound more neutral or more explicitly conditional: if

So Arabic could sometimes use another structure, but إلا إذا is very natural here for unless / only if.

In other words, this sentence is not just grammatically correct; it is also idiomatic MSA.