a vista de ojos

idiomatic

（慣用句）自分の目で

English Meaning

(idiomatic) with one's own eyes

El explorador observó el espectacular fenómeno a vista de ojos durante su expedición.

探検家は自分の目でその壮大な現象を観察しながら、遠征を続けました。

The explorer observed the spectacular phenomenon with his own eyes during his expedition.