expression, godan verb (-u)
lose one's eyesight; go blind
Rare, literary expression. The kanji 明 is used in its classical meaning of 'sight' or 'vision'. In modern Japanese, 視力を失う or 失明する are far more common.
彼は病のために明を失った。
He lost his eyesight due to illness.
A classical Chinese-derived expression. 明 (mei) originally meant 'brightness' and by extension 'sight' or 'vision'. Combined with 失う (ushinau, 'to lose'), it forms a literary phrase for losing one's eyesight.