N-COUNT [usually singular]令人大开眼界的事物 If you describe something as an eye-opener, you mean that it surprises you and that you learn something new from it. 令人大开眼界的事物 [informal]
This summer's tour was an eye-opener for her. For the first time ever, the halls were not fully booked.
今夏的旅游让她大开眼界。有史以来,礼堂第一次没有预订满。
Writing these scripts has been quite an eye-opener to me. It proves that one can do anything if the need is urgent.