Pituitary Apoplexy: This condition is characterized by sudden hemorrhage or infarction of the pituitary gland, which can compress the surrounding structures including the optic chiasm and nerves, leading to acute visual loss, ptosis, and ophthalmoplegia. The acute onset and combination of symptoms make this a highly plausible diagnosis.

Diabetic Third Nerve Palsy: Diabetes can cause an aneurysm or infarction of the third cranial nerve, leading to ptosis and ophthalmoplegia. However, the absence of light response and acute visual loss might suggest a more extensive process.
Cavernous Sinus Thrombosis: This condition can cause multiple cranial nerve palsies, including the third, fourth, and sixth nerves, leading to ptosis and ophthalmoplegia. It can also affect the optic nerve, causing visual loss.
Tolosa-Hunt Syndrome: An inflammatory condition affecting the cavernous sinus or superior orbital fissure, which can cause painful ophthalmoplegia and might lead to visual disturbances.

Aneurysm of the Posterior Communicating Artery (PCoA): An aneurysm of the PCoA can compress the third cranial nerve, causing ptosis and ophthalmoplegia. If it ruptures, it can lead to subarachnoid hemorrhage, which is life-threatening.
Carotid Artery Dissection: Dissection of the carotid artery can lead to ischemia of the optic nerve and the nerves controlling eye movement, resulting in visual loss and ophthalmoplegia.

Wernicke's Encephalopathy: A condition caused by thiamine deficiency, which can lead to ophthalmoplegia among other symptoms. However, it typically presents with a more gradual onset and additional symptoms like ataxia and confusion.
Miller Fisher Syndrome: A rare variant of Guillain-Barré Syndrome, characterized by ophthalmoplegia, ataxia, and areflexia. It is less likely given the acute visual loss and ptosis without mention of other systemic symptoms.