Which condition does NOT fall under post-traumatic causes of loss of vision?

The condition that does not fall under post-traumatic causes of loss of vision is posterior reversible encephalopathy. This condition is a neurological syndrome associated with various systemic problems such as hypertension, renal failure, or certain medications, rather than direct trauma to the eyes or surrounding structures.

In contrast, optic nerve avulsion, orbital blow-out fracture, and retinal detachment are all conditions that can result from trauma. Optic nerve avulsion occurs when the optic nerve is detached due to severe trauma to the eye or head, directly impacting vision. An orbital blow-out fracture is a fracture of the bones surrounding the eye, which can occur from blunt force trauma and may lead to vision impairment due to muscle entrapment or damage to the optic nerve. Retinal detachment can also occur as a result of trauma and leads to loss of vision due to the retina being pulled away from its normal position in the eye.

Thus, posterior reversible encephalopathy is not directly linked to trauma but rather to other medical conditions, making it the correct answer.