[sa547]

Spoiler for The Glass Eye:

Maybe Mei thinks that the glass eye is very special, but personally I think the girl is really a psychic, only that she prefers to hide this ability out of the fear of being accused as the Another and lynched in public by "witch-hunters".

True and physically, she cannot see with that glass eye, but perhaps Mei has a psychic ability to sense who is the Another, a possible sixth sense, able to "see" with her mind. And it's possible she obtained it somewhere after her other eye developed an infection.

Yet it seems that she prefers to withhold the identity of this Another, the Dead One, except until the last and critical stage.