Krótkowzroczność, dalekowzroczność i astygmatyzm to wady wzroku.

In this sentence, to works as a linking word meaning something like are in definitions or classifications.

So:

Krótkowzroczność, dalekowzroczność i astygmatyzm to wady wzroku.
= Myopia, farsightedness, and astigmatism are vision defects.

Polish very often uses to in sentences of the type:

• X to Y
• A i B to C

Examples:

• To jest problem. = This is a problem.
• Kawa to mój ulubiony napój. = Coffee is my favorite drink.
• Psy to zwierzęta. = Dogs are animals.

You could sometimes rephrase with są, but to is extremely natural here because the sentence is defining/classifying these conditions.

Because the subject is a list of three things:

• krótkowzroczność
• dalekowzroczność
• astygmatyzm

Together, they are being identified as wady = defects / impairments / disorders.

The singular is:

• wada = defect

The plural is:

• wady = defects

So:

• Astygmatyzm to wada wzroku. = Astigmatism is a vision defect.
• Krótkowzroczność, dalekowzroczność i astygmatyzm to wady wzroku. = ... are vision defects.

Because wada usually takes the noun after it in the genitive case.

So:

• wada czego? = defect of what?
• wada wzroku = defect of vision / vision defect

Here:

• wzrok = eyesight, vision
• wzroku = genitive form of wzrok

This is a very common Polish pattern:

• problem zdrowia = health problem
• objaw choroby = symptom of a disease
• wada serca = heart defect
• wada wzroku = vision defect

So wzroku is there because Polish expresses of vision with the genitive.

Most of the main nouns here are in the nominative, except wzroku.

Breakdown:

• krótkowzroczność — nominative singular
• dalekowzroczność — nominative singular
• astygmatyzm — nominative singular
• wady — nominative plural
• wzroku — genitive singular

Why?

The first three nouns form the subject-like part of the sentence.
Wady is also nominative because it is the predicate noun after to.
Wzroku is genitive because of the phrase wada wzroku.

Yes. Nouns ending in -ość are normally feminine in Polish.

So:

• ta krótkowzroczność
• ta dalekowzroczność

This ending is very common in abstract nouns, for example:

• miłość = love
• trudność = difficulty
• możliwość = possibility

In your sentence, both krótkowzroczność and dalekowzroczność are feminine singular nouns.

Because it is a different kind of noun morphologically.

• astygmatyzm ends in -yzm, which is typically a masculine noun ending in Polish
• krótkowzroczność and dalekowzroczność end in -ość, which is typically feminine

So:

• ten astygmatyzm = masculine
• ta krótkowzroczność = feminine
• ta dalekowzroczność = feminine

Even though all three words name eye conditions, they do not have to share the same grammatical gender.

Polish stress is usually on the second-to-last syllable.

Approximate stress:

• krót-ko-wzrocz-NOŚĆ
• da-le-ko-wzrocz-NOŚĆ
• a-styg-ma-TYZM
• WA-dy
• WZRO-ku

A few pronunciation notes:

• ó sounds like u
• cz sounds roughly like ch in chop
• szcz is a cluster learners often find hard, but here you mainly have wzrocz
• rz usually sounds like zh as in measure
• wz at the beginning of wzroku can be tricky; the w is like English v

Very rough approximations:

• krótkowzroczność ≈ kroot-koh-vzrochnoshch
• dalekowzroczność ≈ dah-leh-koh-vzrochnoshch
• astygmatyzm ≈ ah-stig-ma-tizm

These are only rough guides; the real Polish sounds are more precise than English spelling can show.

Because i means and, and in a simple list Polish normally does not use a comma before i.

So this is standard:

• A, B i C

Exactly like:

• jabłka, gruszki i śliwki = apples, pears and plums

Polish generally does not use the Oxford comma in ordinary writing, so the punctuation here is completely normal.

Yes. If you want to talk about just one condition, you would use the singular:

• Krótkowzroczność to wada wzroku.
• Dalekowzroczność to wada wzroku.
• Astygmatyzm to wada wzroku.

Here:

• wada = singular
• wady = plural

That is a very useful pattern:

• X to wada wzroku.
• X, Y i Z to wady wzroku.

Yes, wady wzroku is a very natural and common Polish expression.

It can mean things like:

• vision defects
• refractive errors
• eyesight problems

Depending on context, English may translate it differently. In everyday language, vision problems or eye defects may fit. In a more medical context, refractive errors may sometimes be the best translation, especially if the topic is myopia, hyperopia, and astigmatism.

So the Polish phrase is normal and idiomatic, even if the best English wording changes by context.

A little, yes, but the original order is the most neutral.

Natural version:

• Krótkowzroczność, dalekowzroczność i astygmatyzm to wady wzroku.

You could also say:

• Wadami wzroku są krótkowzroczność, dalekowzroczność i astygmatyzm.

This version is more formal or stylistically different, and it uses:

• wadami wzroku = instrumental plural

For a learner, the original sentence with to is simpler and more common as a clear definition.

Yes, but with different frequency.

• krótkowzroczność is common
• astygmatyzm is common
• dalekowzroczność is also correct and used, though in everyday speech people may sometimes use simpler explanations depending on context

These are normal standard Polish terms, not obscure specialist vocabulary. You would see them in medical texts, optician’s offices, school materials, and general health discussions.