Indeed that does look nasty.
I can't see any head parts, but I wonder if this is a cluster of engorged ticks ... probably Ixodes frontalis ... as these have a habit of attaching themselves to the eyelids of birds? I can't imagine what else it might be in fact.
On the left eyelid, there appears to be a small one that clearly hasn't done much feeding as yet, not having swelled with blood like the others.
Ticks normally drop off when they are full, but with an infestation this severe this poor bird may become quite debilitated by the blood-loss, or through secondary bacterial or viral infections.
It's encouraging that it seems to be coping thus far though.