What term describes a biphasic ocular oscillation with at least one slow phase?

The term that describes a biphasic ocular oscillation with at least one slow phase is nystagmus. Nystagmus is characterized by a rhythmic, involuntary movement of the eyes, which includes a fast phase and a slow phase. This condition can occur in various forms, such as congenital or acquired, and it can result from various underlying causes, including neurological disorders or vestibular issues.

In contrast, strabismus refers to a misalignment of the eyes, where both eyes do not focus on the same point simultaneously. Diplopia, commonly known as double vision, occurs when a person sees two images of a single object due to issues in eye alignment or muscle control. Ptosis involves the drooping or falling of the upper eyelid and does not pertain to oscillatory eye movements. Thus, nystagmus is the only term that accurately fits the description provided in the question.