Рецепт на очки не меняется, если только не меняется острота зрения.

In Russian, рецепт на что-то is the normal way to say a prescription for something, especially in medical and pharmacy-related language.

So:

• рецепт на очки = a prescription for glasses
• рецепт на лекарство = a prescription for medicine

Here на does not literally mean physical movement onto something. It is just the standard preposition used in this expression.

Also note that очки is in the accusative case after на, but because очки is an inanimate plural noun, its accusative form looks exactly like the nominative:

• nominative: очки
• accusative: очки

Russian normally uses очки only in the plural, just like English usually says glasses rather than a glass when talking about eyewear.

So:

• очки = glasses
• there is no normal everyday singular form meaning one pair of glasses

This kind of noun is called plural-only in practice for ordinary usage.

Yes, рецепт and English recipe are historically related, but in modern Russian рецепт usually means either:

1. a recipe for cooking, or
2. a medical prescription

In this sentence, it clearly means prescription, specifically an eyeglass prescription.

So рецепт на очки means glasses prescription or prescription for glasses, not a cooking recipe.

Меняется is the reflexive form of менять / изменить, and here it means changes or gets changed in the sense of undergoes change.

Compare:

• Он меняет рецепт. = He changes the prescription.
  (someone actively changes it)

• Рецепт меняется. = The prescription changes.
  (the prescription itself changes / is subject to change)

In this sentence, the idea is not that someone is actively changing it right now, but that it does not change as a general rule.

So не меняется is the natural choice.

Because the sentence has two separate clauses, and each has its own verb:

• Рецепт на очки не меняется
• если только не меняется острота зрения

Literally:

• The glasses prescription does not change
• unless visual acuity changes

So the repetition is completely normal. The sentence is saying one thing does not change, except in the case where another thing changes.

This is one of the most important points in the sentence.

Если только не is a set expression that often means unless.

So:

• если только не меняется острота зрения = unless visual acuity changes

Even though it looks word-for-word like if only not, you should not interpret it literally here.

A helpful way to remember it:

• если = if
• если только can sometimes mean only if
• если только не often means unless

So in this sentence, the natural English equivalent is simply:

• The prescription for glasses does not change unless visual acuity changes.

Because Russian and English do not build this kind of clause in the same way.

In Russian, если только не + verb is a normal idiomatic pattern meaning unless. The не is part of that pattern.

So although English says:

• unless visual acuity changes

Russian says:

• если только не меняется острота зрения

You should learn если только не as a chunk rather than trying to translate each word separately every time.

Острота зрения literally means sharpness of vision, which in natural English is usually visual acuity.

Breakdown:

• острота = sharpness, acuity
• зрения = of vision / of sight

Here зрения is in the genitive case because Russian often uses the genitive to show a relationship like of:

• острота зрения = acuity of vision
• цвет глаз = color of eyes
• центр города = center of the city

So this is a very common noun + genitive structure.

Both word orders are possible in Russian.

• Острота зрения не меняется is neutral and straightforward.
• не меняется острота зрения is also natural and slightly more focused on the verb phrase does not change / changes.

Russian word order is more flexible than English word order. Speakers often move words around for emphasis, rhythm, or style, while the cases show the grammatical relationships.

So this sentence is not unusual. It just sounds a bit more flowing in this structure:

• Рецепт на очки не меняется, если только не меняется острота зрения.

Not necessarily. In Russian, the present tense is often used for general truths, rules, or usual situations, just like in English.

So here не меняется means:

• does not change
• doesn’t usually change
• is not changed under normal circumstances

This is a general statement, not necessarily something happening at this exact moment.

Меняется is from the imperfective verb меняться.

That matters because the sentence describes a general ongoing rule or typical situation, not one completed change.

• меняться = to change, to be changing, to undergo change
• imperfective = process, repeated action, general fact

A perfective verb would suggest a single completed change, which would not fit as naturally here.

So не меняется is exactly what you would expect in a sentence describing what normally happens.

Yes. A simpler but very close version would be:

• Рецепт на очки не меняется, если не меняется острота зрения.

That means essentially the same thing:
The prescription for glasses does not change if visual acuity does not change.

However, если только не is stronger and closer to unless in English. It emphasizes the exception more clearly:

• It doesn’t change, unless visual acuity changes.

So the original version is a bit more idiomatic for expressing that idea.

Yes, рецепт на очки is normal and understandable.

Other possible expressions include:

• рецепт для очков — possible, but less standard in this context
• предписание на очки — more formal or less common in everyday speech
• оптический рецепт — possible in specialist contexts, but not the usual everyday phrase

So for a learner, рецепт на очки is the best phrase to remember.