The eyes signify the intention (Yi) of a movement. During the postures, focus wherever your intention is; the eyes shouldn’t blink.
In between postures, during connecting moves, the eyes can ‘rest’.
This applies to both taiji and qigong, i.e. in the Daoyin Qigong exercises, the head is often required to turn to left or right. Use the eyes to signify the intention.
Photo: Prof. Li Deyin in Strike Tiger.