slit lamp slit lamp in ophthalmology and optometry, a slit lamp is an instrument consisting of a high-intensity light source that can be focused to shine a thin sheet of light into the eye. it is used in conjunction with a biomicroscope. the lamp facilitates an examination of the anterior segment and posterior segment of the human eye, which includes the eyelid, sclera, conjunctiva, iris, natural crystalline lens, and cornea. the binocular slit-lamp examination provides a stereoscopic magnified view of the eye structures in detail, enabling anatomical diagnoses to be made for a variety of eye conditions. a second, hand-held lens is used to examine the retina. eye examination with the aid of a slit lamp. side view of a slit lamp machine. cataract in human eye: magnified view seen on examination with the slit lamp history two conflicting trends emerged in the development of the slit lamp. one trend originated from clinical research and aimed to apply 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. the first man credited with developments in this field was hermann von helmholtz (1850) when he invented the ophthalmoscope. in ophthalmology and optometry, the instrument is called a "slit lamp", although it is more correctly called a "slit lamp instrument". today's instrument is a combination of two separate developments, the corneal microscope and the slit lamp itself. the first concept of a slit lamp dates back to 1911 credited to allvar gullstrand and his "large reflection-free ophthalmoscope." the instrument was manufactured by zeiss and consisted of a special illuminator connected to 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 was not 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 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 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, new slit lamps were introduced which took advantage of new technologies. the last major development was in 1996 in which included new slit lamp optics.