A látásélesség és a dioptria fontos.

A is the Hungarian definite article, so here it means the.

Hungarian has two forms of the definite article:

• a before a consonant sound
• az before a vowel sound

So:

• a látásélesség
• a dioptria

both use a because látásélesség and dioptria begin with consonant sounds.

Also, unlike English, Hungarian uses the same definite article for singular and plural.

Because in Hungarian, when two definite nouns are joined by és (and), it is very normal to repeat the article before each noun.

So the standard pattern is:

• a látásélesség és a dioptria
• a fiú és a lány
• a könyv és a füzet

English sometimes repeats the and sometimes does not, but in Hungarian, repeating it is usually the safest and most natural choice for learners.

In Hungarian, the verb to be is often omitted in the present tense, third person when the predicate is a noun or adjective.

So:

• A látásélesség fontos. = Visual acuity is important.
• A dioptria fontos. = The diopter is important.

No separate word for is appears.

But in other persons or tenses, the verb is there:

• Fontos vagyok. = I am important.
• Fontos volt. = It was important.
• Fontos lesz. = It will be important.

Because fontos is the predicate adjective here, not an adjective directly attached to a noun.

This sentence means:

• The visual acuity and the diopter are important.

So fontos is saying something about the subject.

Compare:

• fontos dioptria = important diopter
  Here the adjective directly modifies the noun.

• A dioptria fontos. = The diopter is important.
  Here fontos is the predicate.

So the end position is natural because the sentence structure is basically:

• subject + predicate

This is a very common learner question.

With two singular nouns joined by és, Hungarian often allows a singular predicate in broad, general statements, especially when the two items are treated together as one topic.

So:

• A látásélesség és a dioptria fontos.

is natural.

You may also hear or see:

• A látásélesség és a dioptria fontosak.

That version emphasizes the two items more clearly as separate things that are important.

So in practice:

• fontos = very natural in a general statement
• fontosak = also possible, with clearer plural agreement

Yes, it is one word, and that is very typical of Hungarian.

It is a compound:

• látás = vision, seeing
• élesség = sharpness, acuity

Together:

• látásélesség = visual acuity

Hungarian forms many technical or abstract terms this way, by combining meaningful parts into a single compound word.

You can also notice these endings:

• -ás / -és often makes a noun from a verb
• -ság / -ség often makes an abstract noun

So the word is quite transparent once you get used to Hungarian word-building.

Yes. Hungarian word order is flexible, and it often depends on focus and information structure rather than a rigid English-style pattern.

The given sentence:

• A látásélesség és a dioptria fontos.

is a neutral statement.

You could also say:

• Fontos a látásélesség és a dioptria.

This puts more attention on fontos: What is important? Visual acuity and the diopter.

So both are possible, but they do not feel exactly the same in emphasis.

A simple guide:

• a = short aw
• látásélesség = roughly LAA-taash-ay-lesh-shayg
• és = aysh
• dioptria = roughly DEE-op-tree-aw
• fontos = FON-tosh

A few useful pronunciation notes:

• á is a long vowel
• é is also a long vowel
• Hungarian s sounds like English sh
• Stress normally falls on the first syllable of each word

So:

• LÁ-tá-sé-les-ség
• DI-op-tri-a
• FON-tos

all have first-syllable stress.