Half opened eyes when exposed to sunlight
Solution 1:
Squinting.
From American Heritage:
- To look with the eyes partly closed, as in bright sunlight.
Solution 2:
dazzle
to lose clear vision especially from looking at bright light
https://www.merriam-webster.com/dictionary/dazzle
Solution 3:
One could grimace because of the bright light, but that's a whole facial movement, not just eyes.