A method for conserving energy in an eye tracking system comprising at least two cameras (CA1, CA2, CB1, CB2) configured to register eye images of at least one eye of a subject, which method is performed in at least one processor and comprises: obtaining eye images from at least one camera in a subset of the at least two cameras (CA1, CA2, CB1, CB2); determining a first pupil parameter (PP 1) based on a first eye image (D A1, D B1) of said eye images; determining a second pupil parameter (PP 2) based on a second eye image (D A1, D A2, D B1, D B2) of said eye images; comparing the first and second pupil parameters (PP 1, PP 2) to one another to obtain a test parameter; checking the test parameter against at least one operation criterion; and in response thereto assigning a respective operation state (OP 1, OP 2, OP 3, OP 4) to at least one camera in the subset of the at least two cameras (CA1, CA2, CB1, CB2), characterized in that the respective operation state involves one of: operating the camera at a high frame rate, if the test parameter indicates that the eye image from the camera fulfills a first operation criterion; operating the camera at a reduced frame rate being lower than the high frame rate, if the test parameter indicates that the eye image from the camera fulfills a second operation criterion, however not the first operation criterion; the camera being in a standby mode, if the test parameter indicates that the eye image from the camera fulfills a third operation criterion, however neither the first nor the second operation criterion; and the camera being powered off, if the test parameter indicates that the eye image from the camera does not fulfil any of the first, second or third operation criteria. obtaining eye images from at least one camera in a subset of the at least two cameras (CA1, CA2, CB1, CB2); determining a first pupil parameter (PP 1) based on a first eye image (D A1, D B1) of said eye images; determining a second pupil parameter (PP 2) based on a second eye image (D A1, D A2, D B1, D B2) of said eye images; comparing the first and second pupil parameters (PP 1, PP 2) to one another to obtain a test parameter; checking the test parameter against at least one operation criterion; and in response thereto assigning a respective operation state (OP 1, OP 2, OP 3, OP 4) to at least one camera in the subset of the at least two cameras (CA1, CA2, CB1, CB2), characterized in that the respective operation state involves one of: operating the camera at a high frame rate, if the test parameter indicates that the eye image from the camera fulfills a first operation criterion; operating the camera at a reduced frame rate being lower than the high frame rate, if the test parameter indicates that the eye image from the camera fulfills a second operation criterion, however not the first operation criterion; the camera being in a standby mode, if the test parameter indicates that the eye image from the camera fulfills a third operation criterion, however neither the first nor the second operation criterion; and the camera being powered off, if the test parameter indicates that the eye image from the camera does not fulfil any of the first, second or third operation criteria. operating the camera at a high frame rate, if the test parameter indicates that the eye image from the camera fulfills a first operation criterion; operating the camera at a reduced frame rate being lower than the high frame rate, if the test parameter indicates that the eye image from the camera fulfills a second operation criterion, however not the first operation criterion; the camera being in a standby mode, if the test parameter indicates that the eye image from the camera fulfills a third operation criterion, however neither the first nor the second operation criterion; and the camera being powered off, if the test parameter indicates that the eye image from the camera does not fulfil any of the first, second or third operation criteria.