Slit Lamp - History

History

To fully understand the development of the slit lamp one must consider that with this invention and its improvements, it had to be accompanied by the introduction of new examination techniques. Two conflicting trends emerged in the development of the slit lamp. One trend originated from clinical research and aimed at an increase in functions and the introduction and application of the increasingly complex and advanced technology of the time The second trend originated from ophthalmologic practice and aimed at technical perfection and a restriction to useful methods and the applications of the instrument. The first man credited with developments in this field was Hermann Von Helmholtz (1850) when he invented the ophthalmoscope.

In ophthalmology and optometry, the term “slit lamp” is the most commonly referred to term however it would be more correct to call it the “slit lamp instrument”. Today’s instrument however is a combination of two separate developments in instruments. The two developments are the corneal microscope and that of the slit lamp itself. Though the slit lamp is a combination of these two developments, the first concept of the slit lamp dates back to 1911 credited to Alvar Gullstrand and his “large reflection-free ophthalmoscope.” The instrument was manufactured by the company Zeiss and consisted of a special illuminator that was connected by a small stand base through a vertical adjustable column. The base was able to move freely on a glass plate. The illuminator employed a Nernst glower which was later converted into a slit through a simple optical system. However, the instrument never received much attention and the term “slit lamp” did not appear in any literature again until 1914.

It wasn’t until 1919 that several improvements were made to the Gullstrand slit lamp made by Vogt Henker. First, a mechanical connection was made between lamp and ophthalmoscopic lens. This illumination unit was mounted to the table column with a double articulated arm. The binocular microscope was supported on a small stand and could be moved freely across the tabletop. Later, a cross slide stage was used for this purpose. Vogt introduced Koehler illumination, and the reddish shining Nernst glower was replaced with the brighter and whiter incandescent lamp. Special mention should be paid to the experiments that 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 slit projector (slit lamp) made it an easy to handle instrument. For the first time, the axis through the patient’s eye was fixed at a common swiveling axis. This was a fundamental principle that was adopted for every slit lamp instrument developed. A limitation still with the instrument was it lacked a coordinate cross-slide stage for instrument adjustment but only a laterally adjustable chin rest for the patient. 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 presented the further development of 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 then improved again in 1950. In 1950, a company named Littmann redesigned the slit lamp again. 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 old illumination systems to make them brighter and essentially daylight quality. From 1994 onwards, new slit lamps were introduced which took advantage of new technologies. The last major development was in 1996 in which included the advantages of new slit lamp optics. See also "From Lateral Illumination to Slit Lamp - An Outline of Medical History"