Polycoria

Polycoria is the medical term for having multiple pupils in a single eye. It's commonly called "double pupils," or "pupula duplex," since it's normally only two pupils.

In Japanese, the common term for polycoria is choudou 重瞳, literally "stacked pupils," and the technical term is is ta-doukou-shou 多瞳孔症, "multiple pupil condition."

In anime, characters with natural double pupils are almost nonexistent. Honestly, I only know one example, and a pretty well-known one, too:

Character: Kaburagi Shisei 鏑木肆星
Anime: Shinsekai Yori 新世界より (Episode 18)

• Examples

Examples

Another anime example is this one:

Character: Daniel Dickens ダニエル・ディケンズ
Anime: Angels of Death, Satsuriku no Tenshi 殺戮の天使 (Episode 1)

• Daniel has heterochromatic double-pupils artificial eyes, which is kind of cheating, since that's not a natural polycoria.

For reference, some non-anime examples.

Character: Mildred Lawrence ミルドレッド・ローレンス
Manga: Shijou Saikyou no Deshi Kenichi 史上最強の弟子ケンイチ (Chapter 539, 陽動の意味)

Sometimes, the term fukugan 複眼, "compound eye," is mistakenly used toward polycoria.

項羽

黒谷ヤマメ

百目鬼おめめ

あったーーー！！眼球ひとつのなかにひとみが2つあるののぜっっったいかわいいっておもって描いたの　重瞳 pic.twitter.com/XBZ1Xi4Vwf

— 🚒🔥ワズカ🍕🌋2月驚纏よ43b (@wzzc) February 1, 2014

傘乃サキさん、オリキャラの重瞳ちゃんのお名前を考えるの巻。
杏堂 茜芽(ちょうどう あかめ)

杏堂は重瞳と読み方を掛けてるよ！
茜芽は赤い目のあかめ！！！！

かわいいなぁ。ちょーどーさん

画像使い回しごめんて、、、そんな責めんなって、、、 pic.twitter.com/HiMPjD4Vax

— 傘廼 さき (@kasano_saki) November 1, 2019

能天気系殺人鬼娘と重瞳触手娘動かしたいんじゃー！ pic.twitter.com/VB4gbq9A4i

— 神無月 璃琥@やや多忙 (@grave_t_d) October 15, 2015