A device (120, 140) for controlling at least one lens, the device comprising means (121-124, 142, 600, 700) configured to: determine if a user is gazing at the device, and if the user is gazing at the device: determine a distance between the eyes of the user and the device, and control the at least one lens of the device to adjust its focal length based on the determined distance, the means being further configured to: compare the determined distance to a threshold distance which is representative of a transition between a near-vision regime and a far-vision regime of the eyes, wherein the at least one lens is controlled to adjust its focal length to a focal length suitable for the near-vision regime if the determined distance is below the threshold distance, characterized in that the means are configured to determine a distance between the eyes and the device at which the user is holding the device when trying to read small text and to notify the user, if the distance is gradually increasing over time, that an emerging condition of presbyopia is likely. determine if a user is gazing at the device, and if the user is gazing at the device: determine a distance between the eyes of the user and the device, and control the at least one lens of the device to adjust its focal length based on the determined distance, the means being further configured to: compare the determined distance to a threshold distance which is representative of a transition between a near-vision regime and a far-vision regime of the eyes, wherein the at least one lens is controlled to adjust its focal length to a focal length suitable for the near-vision regime if the determined distance is below the threshold distance, characterized in that the means are configured to determine a distance between the eyes and the device at which the user is holding the device when trying to read small text and to notify the user, if the distance is gradually increasing over time, that an emerging condition of presbyopia is likely. determine a distance between the eyes of the user and the device, and control the at least one lens of the device to adjust its focal length based on the determined distance, the means being further configured to: compare the determined distance to a threshold distance which is representative of a transition between a near-vision regime and a far-vision regime of the eyes, wherein the at least one lens is controlled to adjust its focal length to a focal length suitable for the near-vision regime if the determined distance is below the threshold distance, characterized in that the means are configured to determine a distance between the eyes and the device at which the user is holding the device when trying to read small text and to notify the user, if the distance is gradually increasing over time, that an emerging condition of presbyopia is likely. compare the determined distance to a threshold distance which is representative of a transition between a near-vision regime and a far-vision regime of the eyes, wherein the at least one lens is controlled to adjust its focal length to a focal length suitable for the near-vision regime if the determined distance is below the threshold distance, characterized in that the means are configured to determine a distance between the eyes and the device at which the user is holding the device when trying to read small text and to notify the user, if the distance is gradually increasing over time, that an emerging condition of presbyopia is likely.