Mój wzrok się pogorszył.

Because wzrok is a masculine singular noun in Polish.

Possessive words like mój change to match the noun they describe:

• mój = masculine singular
• moja = feminine singular
• moje = neuter singular / non-masculine-personal plural

So:

• mój wzrok = my eyesight
• moja książka = my book
• moje okno = my window

Here, wzrok is masculine, so mój is the correct form.

Wzrok means eyesight, vision, or the sense of sight.

It is not usually the same as eyes (oczy). So:

• bolą mnie oczy = my eyes hurt
• mój wzrok się pogorszył = my eyesight got worse

A native English speaker may want to translate word-for-word from my eyes got worse, but Polish usually uses wzrok when talking about visual ability.

Here się is part of the verb expression pogorszyć się, which means to get worse or to worsen.

Compare:

• pogorszyć coś = to worsen something
  
  • Hałas pogorszył sytuację. = The noise worsened the situation.
• pogorszyć się = to get worse
  
  • Sytuacja się pogorszyła. = The situation got worse.

So in Mój wzrok się pogorszył, the eyesight itself underwent the change.

In many Polish verbs, się does not translate neatly into one English word. It is just a normal part of the verb.

Polish past tense agrees with the gender and number of the subject.

The subject here is wzrok, which is:

• singular
• masculine

So the verb is pogorszył się.

Compare:

• wzrok się pogorszył = eyesight got worse
• sytuacja się pogorszyła = the situation got worse
• zdrowie się pogorszyło = health got worse

That final part of the past-tense verb tells you something about the subject.

Because Polish and English do not divide up past meanings in the same way.

Polish does not have a separate tense that works exactly like the English present perfect. Very often, Polish simply uses the past tense where English uses either:

• got worse
• has gotten worse
• has worsened

So Mój wzrok się pogorszył can match any of those depending on context.

Yes. That is also correct.

Polish word order is more flexible than English. Both of these are natural:

• Mój wzrok się pogorszył.
• Mój wzrok pogorszył się.

The difference is mostly about rhythm, style, and emphasis, not basic meaning.

Also very common is:

• Pogorszył mi się wzrok.

That version is especially natural in everyday speech and literally has something like My eyesight worsened on me. The mi is a dative pronoun and often appears in this kind of sentence.

This is a difference of aspect, which is very important in Polish.

• pogorszył się = perfective
  Focuses on the change as a completed event/result: it got worse.
• pogarszał się = imperfective
  Focuses on the process, duration, or repetition: it was getting worse / used to get worse.

Examples:

• Mój wzrok się pogorszył. = My eyesight got worse.
• Mój wzrok pogarszał się przez kilka miesięcy. = My eyesight was getting worse for several months.

So in your sentence, the speaker is talking about the result of a change.

No. It is a general verb meaning to get worse.

You can use it with many things:

• Sytuacja się pogorszyła. = The situation got worse.
• Pogoda się pogorszyła. = The weather got worse.
• Stan pacjenta się pogorszył. = The patient’s condition worsened.
• Mój wzrok się pogorszył. = My eyesight got worse.

So once you learn pogorszyć się, you can use it in many contexts.

A few parts may be difficult for English speakers:

• mój — roughly mooy
  The ó sounds like u in modern Polish.
• wzrok — roughly vzrok
  The w sounds like English v.
• się — roughly shyeng or shen depending on speech style
  The si before a vowel-like sound gives a soft ś sound.
• pogorszył — roughly po-gor-shył
  The rz here sounds like ż/zh.

A more careful breakdown:

• Mój = mooy
• wzrok = vzrok
• się = sheng / shye
• pogorszył = po-GOR-shył

Stress in Polish usually falls on the second-to-last syllable, so:

• po-gor-SZYŁ

Because Polish has no articles.

English needs words like:

• a
• an
• the

Polish does not. So wzrok can mean:

• eyesight
• the eyesight
• one’s eyesight

The exact meaning is understood from context.

That is why Mój wzrok się pogorszył sounds complete without any article-like word.