Difference between くらい and くらいに


> ...., これ以上ないくらい **に** 大きく目を見開いて、...  
>  she opened her eyes as wide as possible ...

I don't understand what に is doing here. I've seen plenty of examples where
くらい acts adverbially without needing に. So why is it there, and what happens
if I omit it?

If it helps, my literal understanding is to parse it as "to the extent that
there is nothing more than this she widley opened her eyes".

I read [this answer](https://japanese.stackexchange.com/questions/35910/is-
the-word-%E3%81%90%E3%82%89%E3%81%84-a-noun-why-do-we-need-%E3%81%AE-
between-%E3%81%90%E3%82%89%E3%81%84-and-%E3%81%AF%E3%81%9A) for particle の but
that doesn't seem to apply here since に cannot (as far as I know) attach to
ない.

Aside: does 目を見開く have some cultural significance e.g. does it represent
concentration for example? The subject is currently beating a dog with a
broom. It says that she made a 一 shape with her lips (seems like something
you'd do if you were concentrating) and then the above sentence. I would
normally associate wide eyes with fear (I don't think she's scared), but that
would be passive. This sentence is active.




Both ～くらい and ～くらいに can function adverbially, and I don't see a difference in
meaning between:

> これ以上ない **くらいに** 大きく目を見開いて・・・

and

> これ以上ない **くらい** 大きく目を見開いて・・・

Similar examples:

>   * 子供の **ときに** 京都に引っ越しました。/ 子供の **とき** 京都に引っ越しました。
>   * 子供の **ころに** よく遊んだ公園 / 子供の **ころ** よく遊んだ公園
>   * **すぐに** 伺います。 / **すぐ** 伺います。
>   * **まっすぐに** 立ってください。 / **まっすぐ** 立ってください。
>   * **しっかりと** 持つ / **しっかり** 持つ
>   * **ぼんやりと** 眺める / **ぼんやり** 眺める
>

* * *

> does 目を見開く have some cultural significance e.g. does it represent
> concentration for example?

目を見開く _can_ indicate concentration, but here in your example I think it shows
緊張 (tenseness) and/or 興奮 (agitation/excitement?) It can also be used to
describe one's surprise, anger, fear, admiration, seriousness, etc.

* * *

(By the way, 目を[見張]{みは}る typically represents surprise and/or admiration.)




Both ～くらい and ～くらいに can function adverbially, and I don't see a difference in
meaning between:

> これ以上ない **くらいに** 大きく目を見開いて・・・

and

> これ以上ない **くらい** 大きく目を見開いて・・・

Similar examples:

>   * 子供の **ときに** 京都に引っ越しました。/ 子供の **とき** 京都に引っ越しました。
>   * 子供の **ころに** よく遊んだ公園 / 子供の **ころ** よく遊んだ公園
>   * **すぐに** 伺います。 / **すぐ** 伺います。
>   * **まっすぐに** 立ってください。 / **まっすぐ** 立ってください。
>   * **しっかりと** 持つ / **しっかり** 持つ
>   * **ぼんやりと** 眺める / **ぼんやり** 眺める
>

* * *

> does 目を見開く have some cultural significance e.g. does it represent
> concentration for example?

目を見開く _can_ indicate concentration, but here in your example I think it shows
緊張 (tenseness) and/or 興奮 (agitation/excitement?) It can also be used to
describe one's surprise, anger, fear, admiration, seriousness, etc.

* * *

(By the way, 目を[見張]{みは}る typically represents surprise and/or admiration.)

