Rhythmic pupil dilation is called hippus, and everyone that has an eye has it to an extent. The are conditions where it's off balance or too fast or too slow... here's what I found online:
A good understanding of what affects pupil size is important in those "unusual" cases. First, the pupil is not a "thing." It is an empty hole in the center of the iris. The iris, which forms the pupil, consists of a layer of cells containing the pigment melanin, which blocks the light, and two sets of muscles. A ring shaped muscle called the sphincter closes the pupil, and a radial set of muscle fibers called the dilator opens it. Primary input to the sphincter is from the parasympathetic (relaxing) branch of the autonomic nervous system, whereas the dilator is controlled by the sympathetic branch (fighting). Pupil size is primarily determined by the balance between actions of the two branches of the autonomic nervous system. The most important factor that affects pupil size is light. When light is detected by the photoreceptors in the eyes, information is sent via the optic nerve and tract to nuclei in the mid-brain and then on to the Edinger-Wesphal nucleus. Signals to the dilator and sphincter muscles are generated as a result to activity in this nucleus, but other sources of neural innervation beyond those produced by light can also alter activity in this nucleus. Because the coordination required to keep the two systems in balance is not perfect, the pupil is in a constant state of unrest. This is called hippus or pupillary athetosis. Normal hippus is difficult to detect, but exaggerated hippus can result from various pathological states including drug intoxication. It is well known that cocaine affects the sympathetic nervous system and causes dilation, whereas the narcotic analgesics affect the parasympathetic system and cause constriction. Rhythmic pupillary dilation coincident with the pulse suggests aortic insufficiency (Landolfi's sign). LANDOLFI'S SIGN: in aortic regurgitation, systolic contraction and diastolic dilation of the pupil The only reference to hippus in felines I could find is that it's often a result of epilepsy and seizure... and high fevers can cause seizure... Phaewryn http://ucat.us Adopt a New England FIV+ cat: http://ucat.us/FIVadopt.html Special Needs Cat Links (and feline info library): http://ucat.us/domesticcatlinks.html
