ito-me 糸目

In manga and anime, when a character's eyes are drawn as a single horizontal line, the term for that in Japanese is ito-me 糸目, "string eyes," as in a string of yarn. A synonym is hoso-me 細目, "thin eyes."

Character: Brock, Takeshi タケシ
Anime: Pokémon, ポケットモンスター (Episode 5)

• Examples

Examples

The term ito-me applies to the imagery of eyes drawn as a single line, which happens pretty much every time a character's eyes are closed in an anime or manga.

Character: Excel エクセル
Anime: Excel♥Saga, エクセル♥サーガ (Episode 1)

• me wo tojiru
  目を閉じる
  To close one's eyes.
• meimoku
  瞑目
  Closed eyes.
  To pass away. To die.

The term ito-me 糸目 also applies to characters whose eyes are always drawn closed, or rather, always drawn as a single horizontal line, even if the eyes are supposed to be open, given they're actually seeing things. For reference, some examples:

Character: Matoba Jinzaburou 的場甚三郎
Anime: Outbreak Company (Episode 1)

Character: Toujou Ayumu 東城歩
Anime: Gintama 銀魂 (Episode 79)

Character: Yumasaki Walker 遊馬崎ウォーカー
Anime: Durarara!! デュラララ！！ (Episode 1)

Character: Fujii Yakumo 藤井八雲
Anime: Sazan Aizu, ３×３ＥＹＥＳ (Episode 2)

Since the line eyes can be in a single shape, some people came up with terms for different shapes.

糸目って一言で片づけるでは足りないくらい色んなタイプがあって、
どれも魅力的ですよねっていうアレ
あくまで私個人の意見ですがただ適当に一本線をひけば糸目キャラになるってわけではないと思うんですよね
自分は一番左のタイプが好きです pic.twitter.com/tibhuwwOBo

— 黒野 鉛筆 (@orikyararonpa) December 19, 2015

• ~kei ～系
  Class. Sort. Kind. Type.
• nikkori-kei
  ニッコリ系
  Smile type. (bending upwards.)
• kitsune-kei
  キツネ系
  Fox type. (slanted. See: kitsune-me キツネ目.)
• suihei-kei
  水平系
  Horizontal type. (straight.)
• me-toji-kei
  目閉じ系
  Closed-eyes type. (bending downwards.)

The term ito-me 糸目 only applies to eyes drawn as a single line. It doesn't apply to "closed eyes," tojita me 閉じた目, in general. For example, in the picture below there are two styles of closed eyes, and only one is ito-me.

Anime: Yuyushiki ゆゆ式 (Episode 1)

• Left: ito-me 糸目.
• Right: kazari-me かざり目.

Sometimes when a character is relaxed, their closed eyes are drawn as multiple "horizontal lines," yokosen 横線. This isn't called ito-me either, since ito-me is a single line, not multiple.

Anime: Hataraku Saibou はたらく細胞 (Episode 2)

• See sudare-me すだれ目 for details about this type of eye.

If the eyes are drawn as vertical lines, that's called konsento-me コンセント目 instead.