What is the most likely cause of sudden vision loss in a patient with a history of diabetes and hypertension?

Sudden vision loss in a patient with a history of diabetes and hypertension can often be attributed to retinal artery embolism. This condition typically manifests when an embolus (a blood clot or debris) travels to and occludes a branch of the central retinal artery, disrupting blood flow to the retina.

In diabetic patients, the presence of small vessel disease contributes to the formation of plaques and emboli, increasing the risk of artery occlusion. Hypertension further exacerbates vascular compromise and can lead to acute events like embolism. The sudden nature of the vision loss is characteristic of arterial occlusions, distinguishing it from other conditions that may cause gradual vision changes.

While other options like malignant hypertension may lead to vision issues via different mechanisms, such as retinal edema or hemorrhage, they tend to present over a longer duration. Retinal detachment and vitreous hemorrhage are also potential causes of sudden vision loss but are less directly associated with embolic processes and do not have the same clear link to the immediate occlusion pattern seen in retinal artery embolism.

Therefore, given the patient's background and the acute presentation of sudden vision loss, retinal artery embolism emerges as the most likely cause.