Techniques and mechanisms for determining a direction of gaze by a user of an eye-mountable device. In an embodiment, the eye-mountable device includes a first circuit and a second circuit, each comprising a respective photodiode. The second circuit is configured to provide a light response profile that is more linear than a light response profile provided by the first circuit. Light sensing by the first circuit results in generation of a first signal indicating a level of ambient light in a surrounding environment. Other light sensing by the second circuit results in a second signal being generated. A direction of gaze by a cornea of the user is detected based at least in part on the first signal and the second signal. In another embodiment, the first signal is provided to configure the second circuit.