A tracking device (6) for controlling the focus of electroactive spectacles (2), the spectacles (2) comprising electroactive lenses (24, 26), the tracking device (6) comprising: a tracking camera (14), a tracking controller (18), and a transmitter (20); wherein the tracking controller (18) is configured to: capture, via the tracking camera (14), an image (16); detect, in the image (16), a pair of eyes; determine, from the image of the eyes, a target focus; and transmit, via the transmitter (20), a focus message (4) to the spectacles (2), the focus message (4) being indicative of the target focus, and instructive to the spectacles (2) to set the focus of the lenses (24, 26) accordingly.