We investigate channel characterization for wireless body-area networks (WBANs) in medical applications using optical signal transmission. More specifically, we focus on uplink communication from a central coordinator node (CN), placed on the patient's body, to an access point (AP) in a typical hospital room, which is usually referred to as extra-WBAN link. Using a ray-tracing based approach, we quantify the main characteristics of the optical channel while considering the effects of body shadowing and mobility (accounting for body movements and user global mobility inside the room). Based on the presented results, we discuss the impact of the positions of the CN and the AP on the link parameters. We also evaluate the link performance based on the outage probability criterion, and further quantify the performance improvement achieved by using multiple APs in the room.