Slit Lamp (Biomicroscope) PDF

Slit lamp (biomicroscope) Uz: Hiba Mubarak Definition: A low power, binocular biomicroscope with an intense of light source, used to examine the internal structures of the anterior part of the eye and by means of special examine the internal parts. The name slit lamp biomicroscope: Slit:...

Slit lamp (biomicroscope) Uz: Hiba Mubarak Definition: A low power, binocular biomicroscope with an intense of light source, used to examine the internal structures of the anterior part of the eye and by means of special examine the internal parts. The name slit lamp biomicroscope: Slit: a narrow slit beam of very bright light. Lamp: produce by a lamp (illumination system). Bio: to view the biological structure (of the eye). Microscope: under magnification with microscope. Introduction: Instrument uniquely designed to give a magnified three dimensional view of the eye and its structures for quantitative measurements for documentation. Slit lamp biomicroscope was invented in 1911 by Gullstrand. The instrument is called a slit lamp because in its normal mode of operation the light source produces a thin vertical slit of light at the eye. The slit lamp facilitates an examination which looks at anterior segment, or frontal structures, of the human eye, which include (eyelid, cornea, sclera, conjunctiva, iris, anterior chamber, natural crystalline lens and anterior vitreous). History: Purking, in 1823, attempt to develop a type of slit-lamp by using one hand held lamp to magnify and another hand held lens to focus strong oblique illumination. De wecker in 1863, device a portable ophthalmomicroscope that combine a small monocular microscope. Albert and Greenough in 1891, developed a binocular microscope which provided stereoscope which provided stereoscopic view. Gullustrand in 1911, introduced the illumination system which had for the first time a slit diaphragm in it. Has Goldmann in 1933, improvised the microscope in which all the vertical and horizontal adjustments for the lamp and slit-beam were placed on a single mechanical stage. Littmann in 1950, introduced the new optical principle for the biomicroscope. He incorporated the rotatory magnification changer based on the principle of Galilean telescope. Principle of slit lamb biomicroscpe: A narrow slit beam of very bright light produced by lamp. This beam is focused on to the eye which is then viewed under magnification with a microscope. Types of slit lamp biomicroscpe: There are two types of slit lamp biomicroscope: 1) Light source is at the base (bottom) of the instrument: Zeiss slit lamp biomicroscope. 2) Light source is at top of the instrument: Haag Streit slit lamp biomicroscope. Parts of slit lamp: 1. Mechanical system. 2. Observation system. 3. Illumination system. A. Mechanical system: 1. Forehead, chin rest and power supply unit. 2. Joystick arrangement: Movement microscope and illumination system towards and away from the eye and from side and side is achieved through joystick arrangement. 3. Up and down movement arrangement: Obtained through some sort or screw devices. 4. Patient support arrangement: Vertically movable chin rest and the head rest. 5. Fixation target: A movable fixation target greatly facilitates the examination under some condition. 6. Mechanical coupling: Provides a coupling of microscope and illumination system along a common axis of rotation that coincides their focal plane. 7. Magnification control: Include two pair of readily changeable objectives lenses and two sets of eyepieces. B. Observation system:  It consists of two optical elements: 1. An objective. 2. An eyepiece.  It presents to the observer an enlarged image near object.  The objective lens consists of two plano-convex lenses with their convexities put together providing a composite power of +22D.  The eyepieces lens has a +10D.  To overcome the problem of inverted image produce by compound microscope, slit lamp microscope uses a pair of prism between the objectives and eyepieces to reinvent the image.  Most of slit lamp provide a rang of magnification from 6x to 40x.  Observation tube (convergent tube): they are converged at angle of 10- 15 degree, to provide good stereopsis. C. Illumination system: It consist of: Lamp housing unit. Variable light intensity: low, medium and high. Height: adjustable slit height. Angle: variable angle form with the observation system. A bright, focal source of light with a slit mechanisms. The beam of light can be changed in intensity, height, width, director or angle and color during the examination with the flick of lever. Illumination techniques (methods): 1. Diffuse illumination. 2. Direct illumination. 3. Indirect illumination. 4. Retro illumination. 5. Specular illumination. 6. Scletortic illumination. 7. Tangential illumination. 8. Oscillation technique. 1. Diffuse illumination: A wide beam is used, typically at low magnification to obtain a general overview of the eye which then direct subsequent and more details investigation. The structures to be viewed with this technique include: lids, lid margins, puncta, eye lashes, bluber and palpebral conjunctiva, cornea, pupil, iris and tear film. 2. Direct illumination (focal illumination): In this technique both the slit beam and the microscope are focused at the same point. By varying the width of the slit beam, the degree of magnification and the angle between illumination and observation systems, one can move from a general view of the anterior segment to a three dimensional optic section of the cornea, anterior chamber or crystalline lens. The direct illumination: Optic section. Parallelepiped. Conical beam. Optic section: Used primarily to evaluate structural layers of the cornea and lens. Estimating the depth of an abnormality such as corneal foreign body or position of cataract. Anterior chamber angle. The depth of anterior chamber can be observed by Van Herrick’s test in optic section of light is used at corneal limbal area. Parallepiped: Provides a layered view of the cornea and lens. Probably the most commonly used. Broader view with extensive examination. Depth and extent of corneal abrasions, scarring, or foreign bodies. Conical beam: Most useful technique when examining the transparency of the anterior chamber for the evidence of floating cells and flares, as seen in anterior uveitis. Best in darkened room. 3. Indirect illumination: This occur when the microscope is focused directly adjacent to illuminated area. The illumination system must be uncoupled from the observation system for this technique. This technique is useful for examine the fine structures of the iris surface, conjunctiva and cornea. 4. Retro illumination (transmission): This produce when area of interest are illuminated by light reflected from a more posterior surface. For example the cornea can be lit by light reflected from the iris. Since the object of regard is viewed against a bright background, it will appear dark or in shadow. There are two types of retro illumination: 1. Direct retro illumination: the observation and illumination systems coupled. The lesions appear dark against the bright background. 2. Indirect retro illumination: the observation and illumination systems uncoupled. The lesion appear against dark background.  Used to observe lesion or opacities in cornea and lens. 5. Specular reflection: This can be used to image surface and allows assessment of surface texture. It occurs when the observation and illumination systems are set at equal angle to align perpendicular to the structure being observed. This technique is valuable for examining the tear film, the corneal endothelium and the anterior and the posterior surfaces of the crystalline lens. These surfaces generally examined under high magnification. 6. Sclerotic Scatter: This produced by the total internal reflection that occur within the cornea as light is directed onto the limbus. In a clear cornea, the limbus will glow around its circumference while the central area remains dark. Any defect within the cornea (such as edema, haze or infiltrates) will scatter light and can be seen as an area of brightness within the cornea and viewed against the dark background of the pupil or iris. The illumination system is uncouple from the observation system in this technique. 7. Tangential illumination: This technique is used to observe surface texture. Medium to wide beam of moderate height used. Swing the slight lamp arm to the side at an oblique angle. Variable magnification used. Observe: anterior and posterior cornea, iris anterior lens. 8. Oscillation Illumination: Oscillation is a variation of indirect illumination in which the microscope is kept in focus on the structure to be observed and beam is oscillated back and forth alternately resulting in direct and indirect illumination. Fine corneal scars, opacities and other lesion are often isolated more readily by using oscillation than either direct or indirect illumination. Filter illumination: Slit lamp can be supplemented with following filters: Diffuser: used when general, non-focal illumination is required. This can also be used for anterior segment photography. Cobalt blue: used in flourescein examinations as an exciter filter for flourescein examination. Red-free: used to enhance contrast between blood vessels and their surroundings. Neutral density: permitting larger slit widths to be employed without a commensurate increase in brightness as an aid to patient comfort. Yellow: some instruments include a yellow filter for increased patient comfort during prolonged examination. Uses of slit lamp biomicroscope: A. Diagnostic uses: 1. Anterior and posterior segment evaluation. 2. Measurement of IOP (Goldmann applanation tonometry). 3. Tear evaluation (TBUT test). 4. Staining (flourescein, rose bengle). 5. FFA (fundus flourescein angiography) and clinical photography. 6. Assessment of the angle anterior chamber (Gonioscopy). 7. Assessment of corneal thickness (Pachymetry). B. Therapeutic uses: 1. Foreign body removal. 2. Contact lenses fitting and post wear evaluation. 3. Epilation. 4. Insertion of panctal plugs. 5. Laser. Accessory devices: 1. Gonioscopy. 2. Pachymetry. 3. Applanation tonometry. 4. Slit lamp photography. 5. Slit lamp as a delivery system for Argon, Diode and YAG laser.