أخصائي البصريات هنا بالتأكيد.

Because Arabic often leaves out the verb to be in the present tense.

So أخصائي البصريات هنا بالتأكيد literally looks like:

• أخصائي البصريات = the optometrist / optical specialist
• هنا = here
• بالتأكيد = definitely / certainly

In natural English, we add is: The optometrist is definitely here.

This is very normal in Arabic nominal sentences.

Because أخصائي البصريات is an iḍāfa construction, often called a possessive or noun-linked construction.

In an iḍāfa:

• the first noun usually does not take الـ
• the second noun determines whether the whole phrase is definite

Here:

• أخصائي = specialist
• البصريات = optics / optometry / vision science

Since البصريات is definite with الـ, the whole phrase becomes definite:

• أخصائي البصريات = the optometrist / the optical specialist

So even without الـ on أخصائي, the whole phrase can still mean the optometrist.

Yes, it is.

The structure is:

• أخصائي = specialist
• البصريات = optics / vision-related science

Together, literally: specialist of optics

That is how Arabic often expresses professions or specializations. Instead of one single word, Arabic frequently uses:

• profession/type + field

Other similar patterns are:

• أستاذ اللغة العربية = the Arabic teacher
• مدير المدرسة = the school principal
• طبيب الأطفال = the pediatrician

So أخصائي البصريات works the same way.

البصريات literally relates to optics or vision science. In this context, it refers to the field of eye-related optical care, so the phrase means something like:

• optical specialist
• optometrist

Arabic often names professions through their field of specialization rather than using a direct one-word equivalent.

Also, البصريات is not the same as العيون:

• العيون = eyes
• البصريات = optics / visual science / optical field

So this phrase sounds more technical or professional than simply saying eye specialist.

Usually it is closest to optometrist or optical specialist.

A rough distinction is:

• أخصائي البصريات = optometrist / optics specialist
• طبيب عيون = ophthalmologist / eye doctor
• فني بصريات or similar terms = optician, depending on context

In real usage, exact job titles can vary by country, but أخصائي البصريات is generally not the same as طبيب عيون.

هنا means here, and in this sentence it functions as the predicate or part of the predicate idea: where the optometrist is.

So the sentence is basically:

• أخصائي البصريات = subject
• هنا = here
• بالتأكيد = certainly / definitely

A simple way to understand it is:

The optometrist is here, definitely.

بالتأكيد means certainly, definitely, or for sure.

Literally, it comes from تأكيد = confirmation / emphasis / certainty, with the preposition بـ attached.

So the phrase is roughly like:

• بالتأكيد = with certainty / certainly

Arabic often uses prepositional phrases as adverbs, so this is very natural.

The word order can change, although the given sentence is very natural.

For example, you may also see:

• أخصائي البصريات هنا. = The optometrist is here.
• أخصائي البصريات هنا بالتأكيد. = The optometrist is definitely here.
• أخصائي البصريات بالتأكيد هنا. = The optometrist is definitely here.

The differences are mostly about emphasis and style. The original order sounds smooth and idiomatic.

In fully vocalized, careful MSA, it would be approximately:

• أخصائيُّ البصرياتِ هنا بالتأكيدِ

Why?

• أخصائيُّ is the subject of the nominal sentence, so it is nominative
• البصرياتِ is the second term of the iḍāfa, so it is genitive
• بالتأكيدِ is after the preposition بـ, so it is genitive
• هنا is indeclinable, so it does not change

In normal everyday writing, these case endings are usually not written.

They behave differently because of sun letters and moon letters.

• البصريات: the letter ب is a moon letter, so the ل in الـ is pronounced clearly

  • approximately: al-baṣariyyāt

• بالتأكيد: the word after الـ begins with ت, which is a sun letter, so the ل is assimilated

  • approximately: bit-taʾkīd, not bil-taʾkīd

So this sentence gives you both patterns:

• clear al- in البصريات
• assimilated at-/ta- sound in بالتأكيد after بـ