Оптик начинает проверку зрения.

Начинает is the 3rd person singular present-tense form of начинать, which is an imperfective verb.

So:

• начинать = to begin, to start
• начинает = he/she/it begins, is beginning, or sometimes starts

In this sentence, the subject is оптик, which is singular, so the verb is also singular:

• Оптик начинает ... = The optician begins ...

Russian present tense can often cover both simple present and present progressive in English, depending on context.

Because проверку is in the accusative case, which is used here for the direct object of the verb начинает.

The dictionary form is:

• проверка = check, inspection, test

But after начинать when you are beginning something, that thing is the direct object:

• начинать проверку = to begin a check / start an examination

Since проверка is a feminine noun ending in -а, its accusative singular becomes -у:

• nominative: проверка
• accusative: проверку

So:

• Оптик начинает проверку = The optician begins the examination/check

Because зрения depends on проверка and means of vision or of eyesight.

This is a very common Russian pattern:

• X Y-genitive = X of Y

Here:

• проверка = check, test
• зрение = vision, eyesight
• зрения = of vision / of eyesight

So:

• проверка зрения = vision test, literally check of eyesight

This is similar to other Russian noun combinations such as:

• чашка чая = a cup of tea
• центр города = city center, literally center of the city

The basic dictionary form is зрение.

Its forms here are:

• nominative singular: зрение = eyesight, vision
• genitive singular: зрения = of eyesight / of vision

In the sentence, you need the genitive because it follows проверка:

• проверка зрения = vision test

Yes, here оптик means an optician or eye specialist in an optical shop/clinic context.

In this sentence, it refers to a person performing the eye test.

For a learner, it is useful to know that Russian medical and eye-care vocabulary can vary depending on context:

• оптик = optician
• офтальмолог = ophthalmologist
• окулист = eye doctor (older/common word)

So оптик начинает проверку зрения suggests a practical, professional setting where an optician is starting the eye exam.

Yes, absolutely.

• Оптик начинает проверку зрения = The optician begins the eye test.
• Оптик проверяет зрение = The optician is testing/checking eyesight.

The difference is:

• начинает проверку emphasizes the start of the process
• проверяет emphasizes the action itself

Both are natural, but they focus on slightly different moments.

Because Russian has no articles like English a/an/the.

So:

• Оптик can mean an optician or the optician
• проверку зрения can mean a vision test or the vision test

The exact meaning depends on context.

In many learning examples, English may translate it as The optician begins the eye test, but Russian itself does not mark that distinction with an article.

The stress is:

• о́птик
• начина́ет
• прове́рку
• зре́ния

So the full sentence is pronounced approximately:

О́птик начина́ет прове́рку зре́ния.

Stress is very important in Russian, because it is not always predictable.

Yes, Russian word order is more flexible than English word order.

The neutral order here is:

• Оптик начинает проверку зрения.

But other orders are possible, depending on emphasis, for example:

• Проверку зрения начинает оптик.
  = It is the optician who begins the eye test.
• Начинает проверку зрения оптик.
  = More marked or context-dependent, often used for emphasis or narration.

Even though the order can change, the cases help show what each word is doing.

Because the sentence focuses on the process beginning rather than on the completed result.

Russian aspect often works like this:

• начинать = imperfective
• начать = perfective

Compare:

• Оптик начинает проверку зрения.
  = The optician is beginning / begins the eye test.
• Оптик начал проверку зрения.
  = The optician began the eye test.

In the present tense, Russian normally uses only the imperfective for an action happening now. A perfective present usually has future meaning.

So начинает is exactly what you would expect for a present-time statement.

Yes, it is a very common and natural collocation.

• проверка зрения = eye test / vision test / eyesight check

Russian often expresses these kinds of ideas with a noun plus a genitive noun:

• проверка слуха = hearing test
• проверка документов = document check
• проверка здоровья = health check

So проверка зрения is a normal, standard phrase.

A very literal breakdown is:

• Оптик = optician
• начинает = begins / is beginning
• проверку = check / test / examination
• зрения = of eyesight / of vision

So literally:

Optician begins check of vision.

A natural English translation would be:

The optician begins the eye test.
or
The optician starts the vision test.