A control arrangement for an ophthalmic surgical system for phacoemulsifying a lens wherein the system includes an aspiration line for drawing off fluid and shattered lens particles of the eye lens and a phaco handpiece having a needle. The aspiration line runs within the needle and is configured to impart ultrasonic energy to the phaco handpiece for shattering the eye lens via a longitudinal vibration of the needle. The control arrangement includes a transmitter configured to irradiate electromagnetic radiation via the aspiration line and a receiver configured to receive at least a part of the radiation； and, a control unit configured to control an absolute value of a parameter of the ophthalmic surgical system in dependence upon the amount of the received electromagnetic radiation.
