Is it permissible to uncover the eyes or suffice with a head covering (khimar) when wearing the niqab due to headaches?

It is permissible for a woman to uncover one or both of her eyes out of necessity, such as to see the road, provided that this does not lead to an excessive display of the eye sockets or part of the cheeks, and without adorning the eyes with kohl or similar cosmetics. However, uncovering the entire face is not permissible.