tbf we're missing another pair of eyelids, we used to have a nictatating membrane like many other animals do but nowadays that's only visible as a vestige in the corner next to the nose.

look at reptiles, when they blink there's an extra transparent eyelid that slides in from the middle corner, before the main eyelids.

granted, this wouldn't block any more light as it's transparent, but at least it protects a bit better and lets you get gunk off the eyeball more expediently