Optikko sanoi näöntarkastuksen kestävän vain vartin.

Yes:

• Optikko = optician
• sanoi = said
• näöntarkastuksen = the eye test / vision test in a special -n form used here
• kestävän = lasting / would last
• vain = only
• vartin = a quarter of an hour / fifteen minutes

So the structure is literally something like:

The optician said the eye test lasting only a quarter of an hour

but in natural English that becomes:

The optician said that the eye test would only take fifteen minutes.

Finnish does not have articles like a and the.

So optikko can mean:

• an optician
• the optician

depending on context.

The same is true for many Finnish nouns. English has to choose, but Finnish usually leaves that unstated unless context makes it clear.

Because Finnish can report speech in two different ways here.

A very straightforward version would be:

Optikko sanoi, että näöntarkastus kestää vain vartin.

But Finnish also often uses a more compact structure:

Optikko sanoi näöntarkastuksen kestävän vain vartin.

Both mean essentially the same thing.

This second pattern is often called the referative construction. It is common in written Finnish and perfectly normal, though the että version often feels simpler to learners.

Kestävän comes from the verb kestää = to last / to take.

In this kind of reported-speech structure, Finnish does not use a normal finite verb like kestää. Instead, it uses a special -van / -vän form:

• kestää → kestävän
• tulla → tulevan
• olla → olevan

So:

• että version: näöntarkastus kestää
• compact version: näöntarkastuksen kestävän

You can think of kestävän here as the form Finnish uses after verbs like sanoa, luulla, tietää, etc. when reporting what someone said, thought, or knew.

Because in this construction, the subject of the reported idea appears in the genitive form.

Compare:

• että version: näöntarkastus kestää vain vartin
• compact version: näöntarkastuksen kestävän vain vartin

So in the compact structure:

• näöntarkastus → näöntarkastuksen
• kestää → kestävän

This is one of the main things that makes the sentence look difficult at first.

It is a compound word:

• näkö = sight, vision
• näön = genitive form of näkö
• tarkastus = inspection, check, examination

So näöntarkastus is literally something like vision check.

In natural English, that could be:

• eye test
• vision test
• eye examination

depending on context.

Vartti means a quarter, usually a quarter of an hour, so fifteen minutes.

With verbs like kestää, Finnish often uses the -n form for a complete duration in the singular:

• kestää tunnin = last an hour
• kestää päivän = last a day
• kestää vartin = last a quarter of an hour

So vain vartin means only fifteen minutes.

You could also say vain viisitoista minuuttia, but vain vartin is shorter and very natural.

Because English usually shifts the tense a bit after a past reporting verb like said.

Finnish says:

• sanoi = said
• kestävän = the reported action

English often turns that into:

• said that it would take...

even though Finnish does not literally use a separate word meaning would here.

So would take is often the most natural English translation after said, even though the Finnish form itself is not a conditional.

Usually, yes — at least a little.

• Optikko sanoi, että... is very direct and beginner-friendly.
• Optikko sanoi näöntarkastuksen kestävän... is more compact and often feels a bit more written or formal.

Both are correct. If you are learning, the että version is often easier to produce yourself.

There is no comma because this is not an että clause.

Compare:

• Optikko sanoi, että näöntarkastus kestää vain vartin.
  → comma needed before että

• Optikko sanoi näöntarkastuksen kestävän vain vartin.
  → no että clause, so no comma there

The second sentence is one continuous structure rather than a main clause plus a finite subordinate clause.

Yes, word order can change the focus.

Here:

Optikko sanoi näöntarkastuksen kestävän vain vartin.

vain directly emphasizes vartin = only fifteen minutes.

If you move vain, the emphasis changes. For example:

• Optikko vain sanoi... = The optician only said...
• Optikko sanoi vain... = The optician only said...

So in the original sentence, vain is placed exactly where it naturally emphasizes the short duration.