A known slit-lamp apparatus includes a slit projector defining an optical axis and a corneal microscope. A supplement arrangement makes it possible to conduct a laser treatment with the known slit-lamp apparatus. A therapeutic laser beam is reflected coaxially into the projection beam path of the slit projector. An optical displacement arrangement is mounted on the optical axis downstream of where the therapeutic laser beam is reflected in and serves to displace the laser beam and the projection beam horizontally with respect to the optical axis.