Slit Lamp Biomicrospcopy PDF

SLITLAMP (BIOMICROSCOPY) Source: Brien Holden Vision Institute The slit lamp examination (SLE) is used for the binocular examination of the eye from the anterior to posterior segment. More specifically, it is used for: 1. Anterior segment exam - tear film to...

SLITLAMP (BIOMICROSCOPY) Source: Brien Holden Vision Institute The slit lamp examination (SLE) is used for the binocular examination of the eye from the anterior to posterior segment. More specifically, it is used for: 1. Anterior segment exam - tear film to anterior vitreous 2. Posterior segment exam with auxiliary lenses (78D or Hruby) 3. Intraocular pressure by Goldmann tonometry 4. Anterior chamber depth assessment (irido-cornea angle) 5. Contact lens fittings and assessments 6. Gonioscopy 7. Minor surgical procedures 8. Laser delivery system INSTRUMENTATION There are many different types of biomicroscopes with variable features. All biomicroscopes, however, are composed of 2 basic parts that sit on a common pivoting base: OBSERVATION SYSTEM (MICROSCOPE) Binocular eyepieces Magnification control ILLUMINATION SYSTEM Adjustable light beam (variable height, width, angle) Filters (red-free, cobalt blue, diffuser)  METHODS OF ILLUMINATION: 1. DIFFUSE ILLUMINATION - A wide unfocused beam of light directed obliquely toward the eye PROCEDURE 30-45 degrees angle between observation & illumination systems Wide open slit beam Low to medium magnification With or without diffusing filter PURPOSE Generally used to obtain an overall view of the eye and adnexa (lids, lashes, conjunctiva, sclera, cornea, iris) 2. OPTIC SECTION - A thin slit beam (minimum possible < 0.25 mm) that optically slices the tissues examined allowing the visualization of tissue layers and depth. PROCEDURE 30-45 degree angle between observation and illumination systems Thin slit beam (as thin as possible) Medium to high magnification PURPOSE Assess the different layers and zones of the tissue examined Permits the assessment of the depth of anomalies or bodies within a tissue Generally used to evaluate the cornea & lens Used in the van herrick method to assess the depth of the anterior chamber 3. PARALLELEPIPED - A slit beam of 1-2 mm that illuminates a rectangular area of tissues - This optically sections a parallelepiped of the tissue observed providing a layered 3-dimensional view PROCEDURE 30-45 degree angle between observation and illumination systems 2-3 slit beam (slightly wider than an optic section) Medium to high magnification PURPOSE Assess the different layers and zones of the tissue examined in 3-D Assess the depth & extent of abnormalities within a tissue (abrasions, scarring, FB) Allows the simultaneous visualization of the anterior, middle & posterior areas of tissues generally used for the tear film, cornea & lens 4. CONICAL BEAM - Small spot or square of light produced by narrowing the vertical height of a parallelepiped PROCEDURE 40-50 degree angle between observation and illumination systems 2-3 mm spot or 2-3 slit beam both in height & width Initial low magnification gradually increased to high magnification Room must be completely dark & examiner must be dark-adapted Beam is focused in the anterior chamber (localize cornea & lens and focus in between) Normal anterior chamber is optically empty (dark) Compare darkness of AC zones above and below light path to zone in the light path Direct the illumination source from both the nasal and temporal sides PURPOSE Used to evaluate the clarity of the anterior chamber Assess debris in anterior chamber (usually cells & flare or blood)  5. CONICAL BEAM - Small spot or square of light produced by narrowing the vertical height of a parallelepiped PROCEDURE 40-50 degree angle between observation and illumination systems 2-3 mm spot or 2-3 slit beam both in height & width Initial low magnification gradually increased to high magnification Room must be completely dark & examiner must be dark-adapted Beam is focused in the anterior chamber (localize cornea & lens and focus in between) Normal anterior chamber is optically empty (dark) Compare darkness of AC zones above and below light path to zone in the light path Direct the illumination source from both the nasal and temporal sides PURPOSE Used to evaluate the clarity of the anterior chamber Assess debris in anterior chamber (usually cells & flare or blood) METHODS OF OBSERVATION 1. DIRECT PROCEDURE Observation and illumination systems are focused coincidentally The area under observation is thus directly illuminated by the incident light PURPOSE Method most commonly used General examination purposes METHODS OF OBSERVATION 1. DIRECT PROCEDURE Observation and illumination systems are focused coincidentally The area under observation is thus directly illuminated by the incident light PURPOSE Method most commonly used General examination purposes 2. INDIRECT OR PROXIMAL PROCEDURE Observation and illumination systems are not focused coincidentally The incident light is on an area immediately adjacent to the object or area of interest (2 methods): o Focus slit lamp on area to be examined and look adjacent to it (Fig. 17.7)(area examined slightly adjacent to focuses area) o Focus on area to be examined and then off-set slit beam (Fig. 17.8) (better view is obtained because the area to be examined will be in clear focus) PURPOSE Provides ‘softer’ illumination of structures and fine details Useful when a bright direct light source ‘bleaches out’ the area to be seen Used to view the iris, fine vascularization, pigment spots, corneal edema, etc. Figure 17.7 Indirect Illumination Step 1 Figure 17.8 Indirect Illumination Step 2 3. RETRO-ILLUMINATION PROCEDURE Object under observation is illuminated by light reflected from a deeper structure The desired area/object is viewed directly or indirectly using light shining from behind (Fig. 17.9 and 17.10) Any structure can be used to reflect the light including the retina The angle of illumination is generally between 30-45 degree For retinal retro-illumination, however, the angle of the illumination system is between 0 degree-5 degree PURPOSE Provides ‘softer’ illumination of structures and fine details Useful when a bright direct light source ‘bleaches out’ the area to be seen Used to view the iris, fine vascularization, pigment spots, corneal edema, etc. Figure 17.9 Diagram of difference between observation Figure 17.10 Diagram of difference between observation and illumination systems in direct retro-illumination and illumination systems in indirect retro-illumination 4. SCLEROTIC SCATTER PROCEDURE A bright parallelepiped focused on the limbus causes light transmission within the cornea In a normal cornea, light is internally reflected within the cornea A bright halo around the limbus is produced A normal cornea where the internally reflected light travels freely appears clear Corneal abnormalities will cause light scatter and appear gray or white PURPOSE Especially useful to view subtle corneal changes (edema, scars, striae, foreign bodies, etc.)  6. SPECULAR REFLECTION PROCEDURE Parallelepiped beam Initial low magnification Biomicroscope is moved to place observation system on the reflected light from the cornea A bright specular reflection will be seen Gradually increase magnification At this point the angle of incidence = the angle of reflection The tear film will appear on the anterior parallelepiped surface The endothelium will appear on the posterior parallelepiped surface PURPOSE Used to observe irregularities, deposits, or excavations in a smooth surface Especially useful for corneal endothelium and tear film evaluation FILTERED ILLUMINATION PROCEDURE Use of various filters to enhance the assessment of certain structures and abnormalities e.g. cobalt blue, yellowwratten, red-free, neutral density filters Often incorporated to biomicroscope, otherwise can be added PURPOSE Cobalt blue: used with fluorescein dye to visualize corneal staining Yellow wratten: a barrier filter used with fluorescein to visualize corneal staining Red-free: makes blood vessels & rose bengal stain appear black to enhance contrast Neutral density: uniformly decrease illumination intensity VAN HERICK TECHNIQUE - used to assess anterior chamber depth PROCEDURE: Use low to medium magnification. 60 degree angle between arms of the slit lamp with the observation system perpendicular to the eye. Focus an optic section of medium to maximum height exactly at the limbus (Temporal & Nasal). To be sure, focus slit slightly on the cornea initially, and then move it outwards towards the limbus until it begins to widen (indicates that it is bridging the corneo-scleral transition area). Move back inward to the thinnest last observable optic section. Compare the depth of the anterior chamber indicated by the dark shadow (between the iris and cornea) to the thickness of the cornea (indicated by the optic section Establish the ratio between the dark shadow (DAC) and the corneal thickness (CT): Dac = Depth anterior chamber CT = Depth of the cornea Van Herick Grading System Van Herrick Grading System: Grade DAC / CT ~0 0: AC extremely narrow/closed I: < 1/4 II: 1/4 III: 1/4 to 1/2 IV: > 1/2 Source: Van Herick W, Shaffer RN, Schwartz A. Estimation of width of angle of anterior chamber. Am J Ophthalmol 1969;68:626-9.  SLIT LAMP BIOMICROSCOPY OVERVIEW ILLUMINATION METHOD Characteristic Diffuse Illumination Optic Section Parallelepiped Conical section Angle between SL arms 30-45degree 30-45degree 30-45degree 40-50degree Width of slit beam Maximal Minimal 1-2 mm 2-3mm Height of slit beam Maximal Maximal Maximal 2-3mm Filter None, diffuser, None None, Colored None colored Light intensity Variable Maximal Variable Maximal Magnification Low - Medium Medium-High Medium-High Medium-High METHODS OF OBSERVATION Direct Indirect Retro- Specular Dispersion Characteristic Van Herick Illumination Illumination Illumination Reflection Scleral Focus / Slit- Coincident or Coincident or Coincident Coincident Coincident Coincident lamp arm-lock not not 30-45 degree for Angle between cornea; 30-45 degree 30-45 degree 45-60degree 30-45 degree 60 degree SL arms 0-5 degree for lens-iris Optic section Optic section or Optic section Optic section Type of beam or Parallelepiped or Parallelepiped or Optic Parallelepiped Parallelepiped Parallelepiped Section Height of Slit Medium beam Variable Variable Variable Variable Variable - Maximal None, All Filter others None None None None None Intensity of light Variable Variable Variable Medium-High Maximal Medium- High Magnification Variable Variable Medium-High Medium-High Low-High Low-High Table 17.2 Observation Techniques SLIT LAMP ROUTINE ASSESSMENT: 1. Explain the purpose of the test and give proper instructions 2. Appropriately set up o Wash hands o Disinfect chin and forehead rests o Position patient properly with chin & forehead firmly against rests o Align markings on head rest with patient canthi o Dim room illumination o Prepare instrument, set up illumination o Start with the right eye 3. Assess and use efficient & logical sequence to appropriately examine all tissues of the anterior segment: Lids / lashes (superior /inferior), Tear film, Conjunctiva / sclera (temporal/nasal), Cornea, AC angle, iris, Lens, Anterior vitreous, AC clarity, Superior tarsal conjunctiva (lid eversion) 4. Record assessment and findings appropriately Biomicroscopy NS SN CC CC Figure: Example of biomicroscopy examination record