Eye Examination with the Slit Lamp.

1 Ophthalmic Instruments from Carl ZeissEye Examinationwith the Slit Prof. Allvar GullstrandNobel Prize Winner in Physiology and memory1 Eye Examination with the Slit of Slit illumination system .. Slit lamp microscope .. Mechanical system .. Electrical Range of Carl Zeiss slit lamps .. methods types of Observation by optical section .. Direct diffuse illumination .. Indirect illumination .. Retro-illumination .. Scattering sclero-corneal illumination .. Fundus observation and gonioscopy with the slit lamp .. Fluorescence observation and slit lamp microscopy in contact lens fitting.

2 Assessment of lachrymal film .. Other Examination methods .. of findings .. Video documentation .. Digital image recording and editing .. Measurement of intraocular pressure .. Length and angle measurement .. Miscellaneous .. of the slit lamp and development of the photography of the optical section .. the slit lamp is the ophthalmologist's mostfrequently used and most universally applicableexamination instrument. The most important field ofapplication is the Examination of the anterior segmentof the eye including the crystalline lens and theanterior vitreous optics such as contact lenses andadditional lenses permit observation of the posteriorsegments and the iridocorneal angle that are notvisible in the direct optical number of accessories have been developed forslit lamps extending their range of application frompure observation to measurement.

3 Such as formeasuring the intraocular documentation of findings on electronic mediais increasingly gaining importance as it provides aconvenient medium for keeping track of a disease sprogress. It also facilitates the communication bet-ween physician and patient or between use of the slit lamp in contact lens fitting is animportant recent application worth mentioning. Themodern instrument has increasingly gained appli-cations beyond the traditional ophthalmologist 1. Overview of 1 Application ofSL 120 Slit Slit illumination systemThe illumination system is intended to produce a slitimage that is as bright as possible, at a defined dis-tance from the instrument with its length, width, andposition being variable.

4 Today this is achieved usingoptical imaging with the so-called K hler illumination(Fig. 2). The light source Lis imaged in the objective Oby the collector system K. The objective in turnproduces an image at Sin the mechanical slit locatednext to the collector system. The image of the lightsource at O is the exit pupil of the system. K hlerillumination provides a very homogeneous slit imageeven with a structured light source. This is anadvantage over illumination systems imaging the lightsource in the slit and projecting the latter into the eyetogether with the image of the light source. Thismethod was used in 1911 in the first Gullstrand slitlampand is therefore only of historical brightness of the slit image is characterised bythe illuminance of the slit image which depends on theluminance of the light source, the transmission of imaging optics, the size of the exit pupil, and the distance between exit pupil and Design standard slit lamp is comprised of three elements:1.

5 Slit illumination systemGiving the instrument its name2. StereomicroscopeSimilar to that used on other ophthalmic instruments, surgical microscopes3. Mechanical systemConnecting the microscope to the illumination system and allowing for positioning of the instrumentFig. 2 Principle of K hler illuminationThe optical transmission is increased by anti-reflection coatings on all glass surfaces. The light losscaused by reflections is subsequently reduced to even down to in the case of high-gradeantireflection coatings. The total gain in brightness ofthe slit illumination compared to an uncoated systemis about 20%, thus demonstrating the advantagesoffered by modern specially coated light source used on a slit lamp is either a low-voltage incandescent lamp or a halogen lamp .

6 Thelatter being preferred because of its high luminanceand colour to physical laws the light scatteringability and fluorescence of transparent media isenhanced by such high luminance and colourtemperature, allowing diagnostically importantchanges in colour to yellow to be much more easilyrecognised. Modern slit lamps (see Figs. 7 - 10)therefore employ halogen light certain examinations it is not so much an intense slit illumination that is required but a large-field diffuse illumination. For this reason someinstruments provide an insertable ground glass screenat the plane of the exit pupil and of the filamentimage.

7 The optical path is thus interrupted with theground glass screen acting as a secondary Examination methods require the spectralcomposition of the light to be changed ( for fluor-escence observation in contact lens fitting). For thispurpose various filters are provided in the illuminationsystem which can be easily swung into the beam range of filters include exciter filters for fluorescence, green filters for contrast enhancement,and sometimes grey filters for reducing the illumina-tion intensity while maintaining colour Design principlesFig. 3 Optical path in the stereomicroscope of a slit Slit lamp microscopeThe user expects the slit lamp microscope to pro-vide optimum stereoscopic observation with selectablemagnification.

8 The size of the field of view and thedepth of field are expected to be as large as possible,and there should be enough space in front of the microscope for manipulation on the 3 shows the optical path of a stereomicroscopedesigned on the principle of the telescopic telescopic lens systems, larger workingdistances can be achieved when compared to simplemagnifying systems. These systems consist of atelescope and an object-side magnifying lens. Theobject is located in the object-side focal point of themagnifying lens that magnifies the object imageprojecting it virtually to infinity. This image is thenviewed with the respective magnification through of Fig.

9 3:Between objective O(focal length f1) and tube lenses T(f2) there is a separate, parallel optical pathfor each eye. Hence, the object is located in the focalplane of O. Between Oand Ta telescopic system Weach may be fitted (magnification factor g) to vary thetotal vision requires a defined convergenceangle between the two visual axes. This convergenceangle is obtained by a prismatic power in the objectivetransmitted off axis by both beams. The intermediateimages produced by tube lenses Tthrough rotatableprisms are viewed with eyepieces K(f3).The total angular magnification G of the system is calculated by the following formula:f2250 mmG= _____ x gx _____f1f3(mm) 4 Optical diagram of telescopic systemDesign principlesThe stereomicroscopes of our slit lamps use the following instrument principle:Telescopic systemGalilean system with telecentric optical path (Fig.)

10 4)On this system, both optical paths have a commonor main objective. This objective projects the objectimage to infinity which is viewed by a stereo tube thatis basically a pair of telescopes. In practice the slitlamp requires magnifications of between 5x and 50x,the most commonly used being 10x, 16x, and 25x. Themicroscope magnification can be varied by changingthe eyepieces, but a simpler and more elegant solutionis however, a magnification changer using variableoptical elements. When the magnification is changed,the position of the object plane must of course notchange. A tried and tested means of changing themagnification is a Galilean telescope.