Okay, let's tackle this question. The patient has a history of a runny nose and pain over the medial eye, then presents with sudden high fever, prostration, chemosis, proptosis, diplopia on lateral gaze, and optic disc congestion. The key here is to figure out the most likely diagnosis.

First, the symptoms point towards an orbital infection. The medial aspect of the eye and runny nose suggest a sinus origin, maybe ethmoid sinus. The sudden high fever and systemic symptoms like prostration indicate a severe infection. Chemosis (swelling of conjunctiva), proptosis (bulging eye), diplopia on lateral gaze (due to extraocular muscle involvement), and optic disc congestion (papilledema) are signs of orbital cellulitis.

Now, differentiating between orbital cellulitis and preseptal cellulitis is important. Preseptal would have eyelid swelling without proptosis or diplopia. The optic disc congestion here points to increased orbital pressure affecting the optic nerve, which is more severe.

Other options might include abscess, but the sudden onset and systemic symptoms fit orbital cellulitis better. Meningitis could be a complication if the infection spreads, but the eye symptoms are more prominent here. Graves' disease is a chronic condition and doesn't present with fever. So the correct answer is orbital cellulitis.

**Core Concept**
This question assesses the differential diagnosis of acute orbital infections. Orbital cellulitis, typically secondary to ethmoid sinusitis, presents with systemic toxicity, proptosis, chemosis, diplopia (due to restricted extraocular muscle movement), and optic nerve involvement (papilledema). It is distinct from preseptal cellulitis, which lacks retrobulbar signs.

**Why the Correct Answer is Right**
The patient’s symptoms (fever, prostration, chemosis, proptosis, diplopia, and optic disc congestion) indicate a severe retrobulbar infection. The medial eye pain and runny nose point to ethmoid sinus origin. Orbital cellulitis involves the fat and muscles posterior to the orbital septum, leading to increased intraorbital pressure, optic nerve compression (papilledema), and extraocular muscle dysfunction (diplopia on lateral gaze). Immediate intervention is required to prevent vision loss.

**Why Each Wrong Option is Incorrect**
**Option A:** Preseptal cellulitis involves eyelid swelling and erythema without proptosis or diplopia.
**Option B:** Meningitis presents with fever, neck stiffness, and altered mental status, not localized ocular signs.
**Option C:** Graves’ disease causes chronic proptosis, lid retraction, and extraocular muscle thickening without acute fever or chemosis.
**Option D:** Optic neuritis leads to painless vision loss and relative afferent pupillary defect, not chemosis or diplopia.

**Clinical Pearl**
Remember the mnemonic **“COPS”** for orbital cellulitis: **C**onjunctival chemosis, **O**ptic disc edema, **P**roptosis, **S**ystemic symptoms (fever). Differentiate from preseptal cellulitis by the absence of retrobulbar signs. Urgent imaging (CT) and IV antibiotics are critical to prevent vision-threatening complications.

**Correct Answer

✓ Correct Answer: C. Cavernous Sinus Thrombosis