Oculomotor Abnormalities in a Sheep (Ovis aries) Model of Huntington's Disease: Towards a Biomarker for Assessing Therapeutic Efficacy.

Two measures were identified that could distinguish normal from HD sheep; these were the number of PRN oscillations when tested in the dark and the gain (eye movement to head movement ratio) during the VOR when tested in the light. To our knowledge, this is the first study in which eye movements have been quantified in sheep. It demonstrates the feasibility of measuring and quantifying human-relevant eye movements in this species. The HD-relevant deficits show that even in 'premanifest' sheep there are measurable signs of neurological dysfunction that are characterized by loss of control of eye movements.