What is the main regulatory method of the optic nerve?

• A. Sympathetic innervation
• B. Parasympathetic innervation
• C. Autoregulation
• D. Neural adaptation

Answer: (C)

Autoregulation is the main way the optic nerve maintains a stable blood supply. The vessels feeding the optic nerve head adjust their diameter locally in response to changes in perfusion pressure and metabolic needs, so blood flow remains relatively constant even when systemic blood pressure or intraocular pressure fluctuates. This intrinsic mechanism relies on myogenic responses, metabolic signals, and endothelial factors to dilate or constrict vessels as needed. While autonomic nerves (sympathetic or parasympathetic) can influence vascular tone, they are not the primary regulator of optic nerve blood flow. Neural adaptation relates to how neurons respond to stimuli, not to regulating blood supply. So the essential regulatory method here is autoregulation.