kontakuto wo ireta mama nete ha ikemasen.

Yes. In Japanese, コンタクト is a very common shortened form of コンタクトレンズ.

So in this sentence:

• コンタクト = contact lenses / contacts

Even though the full word is not said, the meaning is usually clear from context. This kind of shortening is very common in Japanese.

を marks the direct object of the verb.

Here, the verb is 入れる, which literally means to put in / insert. So the sentence treats the contact lenses as the thing being put into the eyes.

• コンタクトを入れる = to put in contact lenses

So コンタクトを is the object of 入れた.

This is because of the grammar pattern V-ta + まま.

• 入れた = past/plain form of 入れる
• まま = while remaining in that state / without changing that condition

So:

• 入れたまま = with them left in after putting them in
• more naturally in English: while still wearing them / with them still in

The past form before まま does not mean the whole sentence is in the past. It describes a state resulting from a completed action.

まま means as is, in the state of, or without changing.

In this sentence:

• コンタクトを入れたまま = with your contacts still in
• literally: in the state of having put in contacts

This pattern is often used when one action or condition continues while something else happens.

Examples:

• 靴をはいたまま入る = go in with your shoes still on
• 電気をつけたまま寝る = sleep with the lights left on

So here, it means sleeping without removing the contacts first.

This is the grammar pattern:

• てはいけません = must not / should not / it is not allowed to

So:

• 寝てはいけません = you must not sleep

The て-form of the verb is required before はいけません.

In this sentence, the full predicate is:

• 寝てはいけません = must not sleep

And the earlier part tells you the condition:

• コンタクトを入れたまま寝てはいけません
• You must not sleep with your contacts in.

It is written with the same character は, but in this pattern it is not functioning like a regular topic marker.

In てはいけません:

• ては is a set grammatical combination
• it forms part of the prohibition pattern must not do

So it is better to learn てはいけません as one chunk rather than trying to interpret the は separately every time.

In speech, ては often contracts to ちゃ:

• 寝てはいけません → 寝ちゃいけません (more casual sounding)

Yes, 入れる is very natural for contact lenses in Japanese.

Japanese often describes contact lenses as something you put in your eyes:

• コンタクトを入れる = put in contacts

By contrast:

• メガネをかける = wear glasses
• 帽子をかぶる = wear a hat
• シャツを着る = wear a shirt

So even though English often says wear contacts, Japanese commonly uses 入れる because of the physical idea of inserting them.

Yes. てはいけません is a fairly formal or standard way to say must not.

Other versions include:

• コンタクトを入れたまま寝てはだめです。
• コンタクトを入れたまま寝ちゃだめです。
• コンタクトを入れたまま寝ないでください。
  This is more like please don’t sleep with your contacts in.

Nuance:

• てはいけません = formal / rule-like / instructional
• てはだめです = a bit more conversational
• ちゃだめ = casual speech

The original sentence sounds like a warning or instruction you might see from a doctor, package insert, or sign.

Yes. Japanese often leaves out the subject when it is understood from context.

So the sentence does not say あなたは, but the meaning is still:

• You must not sleep with your contacts in.

This omission is extremely common in Japanese.

Yes, that is close to the literal structure, but it is not the most natural English translation.

A more literal breakdown is:

• コンタクトを入れた = having put in contacts
• まま = remaining in that state
• 寝てはいけません = must not sleep

So literally:

• You must not sleep while remaining in the state of having put in contacts.

But natural English is:

• Don’t sleep with your contacts in.

This is a good example of where a direct word-for-word translation sounds unnatural, even though the grammar is clear.

Japanese often puts the condition or situation first, and the main action or judgment at the end.

Structure here:

• コンタクトを入れたまま = with contacts still in
• 寝てはいけません = you must not sleep

So Japanese builds up like this:

1. first describe the condition
2. then give the action
3. finally give the rule/prohibition

This is very normal Japanese sentence structure. The most important grammatical information often comes at the end.

Yes, it is fairly formal and sounds like a rule, warning, or instruction.

You might see or hear it:

• at an eye clinic
• in instructions for contact lenses
• from an optometrist or doctor
• in health or safety guidance

Because てはいけません is strong and instructional, it fits that kind of context very well. In everyday conversation, people might use a softer or more casual version instead.