What term describes uncontrollable eye movement in horses?

The term that describes uncontrollable eye movement in horses is nystagmus. This condition involves involuntary, rapid movements of the eyes, which can be horizontal, vertical, or rotational. In horses, nystagmus may indicate underlying neurological or vestibular disorders, and it can affect the animal's balance and coordination.

The other terms provided refer to different eye-related conditions. Strabismus refers to a misalignment of the eyes, where they do not point in the same direction. Squinting, or closed eyes, is often a sign of discomfort or irritation and can indicate sensitivity to light or an eye injury. Photophobia is an abnormal sensitivity to light, leading to aversion or discomfort when exposed to bright light conditions. Each term is relevant in veterinary medicine but describes different eye issues, making nystagmus the correct term for uncontrollable eye movements.