As a general rule, eyesight won't change upon arriving in Crystallis. Terrible eyesights remain terrible. There are very good oculists all over this world so getting some appropriate glasses is very easy, if ever the character doesn't have glasses already.

In Homura's case-- Since she fixed her eyesight but the fix is dependent of her world's magic, you could choose whether her eyesight would remain fixed or return to its default level of suck. Furthermore, in the case of Puella Magi's characters, they could still have their soul gem, though it would lose all of its properties.