Primates use their eyes to sample the visual world. They also move their eyes constantly to focus on the scenes they are interested in. Because of this, eye movements reflect the brain cognitive states such as attention, motivation, and decision making in real-time. The brain circuits involving in eye movements are also shown to play crucial roles in cognitive functions. Furthermore, patients with cognitive function deficits caused by, for example, neurodegenerative diseases show eye movement deficits. Studying eye movements and the relevant circuits in the brain can be a window to better understand the brain functions. In my presentation, I will introduce a new non-human primate model, the marmosets (Callithrix jacchus) for eye movement research. I will start with their eye movement behaviors in comparison with other primates. Then, I will show you how I identified the critical cortical areas involved in eye movements using anatomical tracing, electrophysiology, and calcium imaging. I further applied optogenetic manipulations to demonstrate the causal contribution of the brain areas to eye movements. At last, I will show you briefly how the eye movement response time changes with the progression of a neurodegenerative model we developed using α-synuclein fibrils injected marmosets.