Answer to the Parasite Case of the Week 660: Cysticercus; larval form of Taenia solium
As noted by Blaine, this is "ocular cysticercosis caused by T. solium, as indicated by a single protoscolex. Coenurosis caused by a zoonotic Taenia is also a possibility, but coenuri have multiple protoscoleces, as do hydatid cysts of Echinococcus. Sparganosis is another cestode infection that can manifest in the eyes, but they do not produce protoscoleces at all." Lots of great eye puns in the comments!
Here are some of the key diagnostic features: