A male Blue-eyed Darner (note the narrow waist on segment 3) perches in the bushes at Cranberry Lake, in Anacortes, WA. This is an older individual, as evidenced by the scuffed up wings and the ragged trailing edge of its left hindwing. From this distance it's clear that something is odd about its right eye, which seems to have a dark spot on it. I came in closer to get a better look.
Now it's clear that the dark spot is actually something that projects out from the eye.
A closer look shows that the dark spot has the same hexagonal grid as in the eye itself. Apparently it resulted from some abnormality in the growth of the eye.
I lifted the dragonfly onto my finger for a better look. The dark spot is on the upper edge of the dorsal fovea, which extends down to a point just behind the primary pseudopupil. The secondary pseudopupils form a nice hexagonal lattice, as one would expect.