View-through sensors each locatable proximate to an eye of a user and for use while the user is engaged in viewing activity. Each view-through sensor has a view-through region that allows the user to view through the sensor. An active peripheral region at least partially surrounds the view-through region and includes multiple light-sensing regions for sensing light reflected from an eye. In some embodiments, the view-through sensor is configured to use environmental light for eye tracking. When the view-through sensor uses environmental light, spatial and temporal information about the intensity of the environmental light can be used to enhance eye-tracking performance. This information can be obtained, for example, from light-sensing regions on the reverse side of the view-through sensor, from an electronic display, or from a forward-facing camera. In some embodiments, the view-through sensor includes light-emitting regions that emit the light that the sensor uses to track eye movement.