Okay, let's tackle this question about parasites in the extraocular muscles. Hmm, first I need to recall which parasites can infect those muscles. The extraocular muscles are the muscles that move the eye, right? So, any parasite that causes myositis or muscle inflammation might be a candidate.

Wait, Toxoplasma gondii is a common one. Toxoplasmosis can affect the eye, causing ocular toxoplasmosis. But does it specifically target the extraocular muscles? Or is it more about the retina? Maybe I'm mixing it up with another parasite.

Then there's Trichinella spiralis, which causes trichinellosis. That's the one from undercooked pork, right? Trichinella larvae encyst in skeletal muscles. Since extraocular muscles are skeletal muscles, maybe they can be affected. I think trichinosis can lead to periorbital edema and eye muscle involvement. That rings a bell.

Another possibility is Onchocerca volvulus, which causes river blindness. But that's more about the skin and eyes, specifically the anterior uvea, not the muscles. Then there's Loa loa, the eye worm, which can migrate under the conjunctiva. But again, not the muscles themselves.

So the key here is to differentiate between parasites that affect the muscles versus the other parts of the eye. Trichinella is known for muscle involvement, including the extraocular muscles. Toxoplasma is more about retinal lesions. So the correct answer is Trichinella spiralis. The other options like Toxoplasma, Loa loa, and Onchocerca are incorrect because they don't primarily infect the muscles. The clinical pearl here is that Trichinella's muscle invasion, including eye muscles, can lead to symptoms like ptosis or diplopia. That's the high-yield fact.

**Core Concept**
The question assesses knowledge of parasitic infections affecting the **extraocular muscles**, which are skeletal muscles controlling eye movement. **Trichinella spiralis** is a nematode whose larvae encyst in skeletal muscles, including extraocular muscles, leading to **trichinellosis**. This is distinct from other ocular parasites like *Toxoplasma gondii*, which primarily affects the retina.

**Why the Correct Answer is Right**
*Trichinella spiralis* larvae migrate to skeletal muscles during the encystment phase after ingestion of undercooked meat. Extraocular muscles are vulnerable to larval invasion, causing inflammation, edema, and impaired eye movement. This muscle-specific tropism is a hallmark of trichinellosis, differentiating it from other parasitic infections. The immune response to larvae triggers myositis, which can lead to periorbital swelling and diplopia.

**Why Each Wrong Option is Incorrect**
**Option A:** *Toxoplasma gondii* causes ocular toxoplasmosis, primarily affecting the retina and choroid, not the extraocular muscles.
**Option B:** *Loa loa* (African eye worm) migrates under the conjunctiva but does not invade muscles.
**Option C:** *Onchocerca volvulus* (river blindness) causes subcutaneous nodules and anterior uve

✓ Correct Answer: C. Cysticercosis