An identification of individual adrenergic and cholinergic nerve terminals would appear to be possible at the ultrastructural level. It is submitted that there exists a significant dual innervation of the feline dilator muscle and to a lesser extent a dual innervation of the feline sphincter muscle. Selective degeneration experiments have been performed showing a rapid degeneration of the specific nerve terminals with sparing of the unaffected fibers.
Geltzer AI. Autonomic Innervation of the Cat IrisAn Electron Microscopic Study. Arch Ophthalmol. 1969;81(1):70-83. doi:10.1001/archopht.1969.00990010072011