**Core Concept**
Central nystagmus refers to involuntary, rhythmic eye movements originating from the central nervous system, particularly due to lesions or abnormalities in the brainstem or cerebellum. This condition can manifest with distinct characteristics that differentiate it from peripheral nystagmus.

**Why the Correct Answer is Right**
Central nystagmus indeed exhibits several unique features. Firstly, it often changes direction, meaning the direction of the nystagmus beats may switch from one to another, such as from left to right to right to left. This is in contrast to peripheral nystagmus, which typically has a fixed direction. Additionally, central nystagmus is not suppressed by optic fixation, a phenomenon where the nystagmus persists even when the patient is asked to fixate on an object. Furthermore, central nystagmus can present with a variety of directions, including horizontal, vertical, or even rotary movements. The combination of these characteristics makes central nystagmus a distinctive entity that warrants careful evaluation and diagnosis.

**Why Each Wrong Option is Incorrect**
**Option A:** Changing direction is indeed a feature of central nystagmus, but stating that it is the only characteristic mentioned in the question would be an oversimplification.

**Option B:** Not suppressed by optic fixation is a key feature of central nystagmus, but it does not exclusively belong to this condition.

**Option C:** Horizontal or vertical movements can be seen in both central and peripheral nystagmus, so this option is too broad and non-specific.

**Clinical Pearl / High-Yield Fact**
When evaluating a patient with nystagmus, it is essential to differentiate between central and peripheral causes. Central nystagmus often requires a thorough neurological evaluation, including imaging studies to rule out underlying brainstem or cerebellar lesions. Peripheral nystagmus, on the other hand, may be associated with vestibular or ocular abnormalities.

**✓ Correct Answer: D. All of the above**