followed Henker's improvements in 1919. On his improvements the Nitra lamp was replaced with a carbon arc lamp with a liquid filter. At this time the great importance of color temperature and the luminance of the light source for slit lamp examinations were recognized and the basis created for examinations in red-free light. In the year 1926, the slit lamp instrument was redesigned. The vertical arrangement of the projector made it easy to handle. For the first time, the axis through the patient's eye was fixed along a common swiveling axis, although the instrument still lacked a coordinate cross-slide stage for instrument adjustment. The importance of focal illumination had not yet been fully recognized. In 1927, stereo cameras were developed and added to the slit lamp to further its use and application. In 1930, Rudolf Theil further developed the slit lamp, encouraged by Hans Goldmann. Horizontal and vertical co-ordinate adjustments were performed with three control elements on the cross-slide stage. The common swivel axis for microscope and illumination system was connected to the cross-slide stage, which allowed it to be brought to any part of the eye to be examined. A further improvement was made in 1938. A control lever or joystick was used for the first time to allow for horizontal movement. Following World War II the slit lamp was improved again. On this particular improvement the slit projector could be swiveled continuously across the front of the microscope. This was improved again in 1950, when a company named Littmann redesigned the slit lamp. They adopted the joystick control from the Goldmann instrument and the illumination path present in the Comberg instrument. Additionally, Littmann added the stereo telescope system with a common objective magnification changer. In 1965, the Model 100/16 Slit Lamp was produced based on the slit lamp by Littmann. This was soon followed by the Model 125/16 Slit Lamp in 1972. The only difference between the two models was their operating distances of 100 mm to 125 mm. With the introduction of the photo slit lamp further advancements were possible. In 1976, the development of the Model 110 Slit Lamp and the 210/211 Photo Slit Lamps were an innovation by which each were constructed from standard modules allowing for a wide range of different configurations. At the same time, halogen lamps replaced the older illumination systems to make them brighter and essentially daylight quality. From 1994 onwards,