Set up the sensors so that both are looking at the same dark or light area slightly offset. As the wheel rotates sensor A sees light first followed by sensor B. Using only one interrupt triggerd by sensor A have the interrupt routine check to see if sensor B is seeing dark or light.
For instance, when turning clockwise sensor A triggers an interrupt and the routine sees that sensor B is still in the dark. Now reverse rotation and when Sensor A triggers the interrupt sensor B is already seeing light. This way the rotation can be checked at any time without having to keep track from startup.
(This isn't homework, is it???)