Ergonomic effects of ambient light had been extensively studied, and the effects of dynamic ambient light attracted interests of an increasing number of researchers. However, related researches on dynamic light were generally focused on the non-visual effects, such as circadian rhythm, emotion, and cognition. Furthermore, studies on dynamic screen brightness were seldom reported. In this paper, we compared the effects of screens with constant and dynamic brightness respectively on ocular physiological parameters, and found that ocular physiological variations in dynamic screen brightness were significantly lower than those in constant screen brightness, suggesting that dynamic brightness caused less ocular fatigue. The mechanism of the ocular fatigue reduction of dynamic screen brightness was likely to be the activation of brightness-sensitive neurons in primary visual cortex.