her eyes were failing

Dear teachers,

What does 'her eyes were failing' mean?

If it says about the sight, why do they use an ending -s?

Thanks in advance,

Olga.

It means that her eyesight was getting worse. When someone's eyes are failing, they are on the way to blindness or very poor vision. The -s is there, I presume, because we have two eyes, nothing more. ;-)