In this paper, we present a wearable optical sensor based on microfiber for monitoring visual fatigue. The sensor consists of a double-layer polydimethylsiloxane (PDMS)enclosed microfiber. It was positioned on the subject's or-bicularis oculi muscle and secured with medical tape to ensure a tight fit against the skin. During a visual display terminal (VDT) task, we tracked various blinking feature signals associated with visual fatigue. As visual fatigue develops, the blinking characteristics observed in this study change significantly, offering a reliable method for the objective evaluation of VDT.