3 Eyes

In anime, sometimes characters' "eyes become 3's," me ga san ni naru 目が３になる. As in, they become drawn as the number 3, the Arabic numeral.

Not to be confused with having three eyes, or a cat mouth （・ω・）

Character: Nobi Nobita 野比のび太
Anime: Doraemon ドラえもん (2005) (Episode 149, ねむりの天才のび太)

• Examples
  • 4 Eyes

Examples

In general, these 3-shaped eyes are used in anime when a character that wears glasses takes off their glasses. Why are they used? Because they're supposed to represent squinting eyes. The upper part of the 3 numeral is the upper eyelid, while the lower part is the lower eyelid.

Character: Kuurubiyuutei Gankyou 空琉美遊亭丸京
Anime: Joshiraku じょしらく (Episode 4)

By the way, sometimes the mouth is drawn as a 3, too, but that represents something like pouting.

Anime: World Trigger, ワールドトリガー (Episode 16)

Glasses characters constantly and semi-permanently wear glasses. A common time they take off their glasses, and consequently may get 3-shaped eyes, is when they go to sleep.

Character: Aizawa Junichi 相沢順一
Anime: Handa-kun はんだくん (Episode 8)

Character: Nanase Yui 七瀬ゆい
Anime: Go! Princess Precure (Episode 3)

Another case is if they lose they glasses.

• メガネを捨て（られ）るアキラ
• お手本のようなメガネキャラ
• 定番ネタ

• megane megane
  メガネメガネ
  Glasses, glasses. (as in: where are my glasses?)

Note that even characters that don't wear glasses can be drawn like this.

Left: Reina レーナ
Right: Mile マイル
Anime: Watashi, Nouryoku wa Heikinchi de tte Itta yo ne! 私、能力は平均値でって言ったよね！ (Episode 10)

• A snot bubble is another symbol used when characters are sleeping.

4 Eyes

Since drawing eyes like 3's is alright, why we stop there? Here, have some number 4 eyes:

Manga: Saiki Kusuo no Psi-Nan, 斉木楠雄のΨ難 (Chapter 72, さわぐ！PK学園文化Ψ（後編）)

• Context: Saiki borrows his father's glasses without permission.
• oi~~ megane kaeshite yo~~
  オイ～～眼鏡返してよ～
  Heey, give [my] glasses back~~
• gaman shite kure chotto me ga "san" ni naru dake daro
  我慢してくれちょっと目が「３」になるだけだろ
  Please endure [it], [all that will happen is that] [your] eyes will become "threes."
• megane ga nai to hotondo mienai-n-da yo~~
  眼鏡がないとほとんど見えないんだよ～
  Without [my] glasses [I] almost can't see.
• yon!?
  ４！？
  Fours!?

Again, not to be confused with having four eyes.