Astigmatism

…(1) normal vision, which focuses an image on the retina; (2) near sighted eye, which focuses an image in front of the retina; (3) farsightedness, which focuses an image behind the retina; (4) astigmatism, which focuses no image anywhere. All of the above (2) to (4) are called refractive errors. …

*Some terminology explanations that mention "astigmatism" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…(1)正視　網膜に像を結ぶもの，(2)近視myopia∥near sighted eye　俗に近眼ともいう。網膜の前方に像を結ぶもの，(3)遠視hyperopia∥farsightedness　網膜の後方に像を結ぶもの，(4)乱視astigmatism　どこにも像を結ばないもの。正視以外の(2)～(4)を屈折異常という。…

※「astigmatism」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報