Ludo mentis aciem

Can anybody comment this phrase from 'O, Fortuna'? I know that 'ludo' means 'I play' (or is it a form of 'ludus'?), 'mentis' - Dativus pluralis from 'mens' - 'mind', 'aciem' - Accusativus singularis from 'acies' - 'point or edge'. Altogether they don't make any sense for me. This is a part of the song:

O Fortuna
velut luna
statu variabilis,
semper crescis
aut decrescis;
vita detestabilis
nunc obdurat
et tunc curat
ludo mentis aciem,
egestatem,
potestatem
dissolvit ut glaciem.

It's...

Ludo mentis aciem