Slit Lamp Examination Techniques

Slit Lamp Examination (SLE)

• Used for binocular examination of the eye, from anterior to posterior segment
• Used for examining the tear film, anterior vitreous, posterior segment using auxiliary lenses, intraocular pressure (Goldmann tonometry), anterior chamber depth, contact lens fittings, gonioscopy, and minor surgical procedures
• Utilizes a laser delivery system

Instrumentation

• Biomicroscopes vary in features and types
• Composed of two basic parts 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

• Diffuse Illumination: Wide, unfocused beam of light, directed obliquely toward the eye, used for general view of the eye and adnexa (lids, lashes, conjunctiva, sclera, cornea, iris)
• Optic Section: Thin slit beam (minimum 0.25 mm), optically slices tissue, examines tissue layers and depth, used for assessing the depth of anomalies or bodies in tissue
• Parallelepiped (3-Dimensional View): 1-2 mm slit beam, illuminates a rectangular area allowing a layered, 3-dimensional view of tissue layers, useful for tear film, cornea, lens
• Conical Beam: Small, spot or square of light, used for evaluating clarity of the anterior chamber, assessing debris in the anterior chamber

Methods of Observation

• Direct: Observation and illumination systems are focused coincidentally, area under observation is illuminated directly, used for general examination purposes
• Indirect/Proximal: Observation and illumination systems are not focused coincidentally, incident light falls on area adjacent to object/area of interest, used for evaluating structures and fine details, useful for viewing iris, fine vascularization, pigment spots, corneal edema

Retro-Illumination

• Object under observation is illuminated using light that's reflected from a deeper structure within or behind the structure
• Usually 30-45 degree angle between observation and illumination systems
• Useful for viewing structures and fine details obscured by direct light or for viewing deeper structures, for example, retina

Sclerotic Scatter

• Bright parallelepiped focused on the light transmission within the cornea which transmits within the cornea
• Useful for viewing subtle corneal changes (edema, scars, striae, foreign bodies)

Specular Reflection

• Parallelepiped beam
• Bright specular reflection is seen from the cornea, gradually increase magnification, tear film on the anterior surface, endothelium on the posterior surface
• Useful for observing irregularities, deposits, or excavations in smooth surfaces, corneal endothelium, and tear film evaluation

Filtered Illumination

• Various filters used to enhance the assessment of certain structures and abnormalities (e.g., cobalt blue, yellow wratten, red-free, neutral density)
• Cobalt blue: used with fluorescein dye to visualize corneal staining
• Yellow wratten: used with fluorescein to visualize corneal staining
• Red-free: used to visualize blood vessels
• Neutral density: uniformly decreases illumination intensity

Van Herick Technique

• Used to assess the anterior chamber depth
• Use low to medium magnification, 60-degree angle between arms of the slit lamp with observation system perpendicular to the eye
• Establish the ratio between the thickness of the anterior chamber (DAC) to the thickness of the cornea (CT) to determine the grading

Slit Lamp Routine Assessment

• Steps for properly conducting a slit lamp examination: explanation of the procedure, appropriate test setup (washing hands, headrests, etc.), proper examination sequence using efficient and logical order, assessment, and recording

Funduscopy

• Color of the fundus varies among individuals, from reddish-orange to more red or tessellated/tigroid appearance
• Optic nerve head (ONH) lies nasal to macula; its dimensions, margins, and cup-to-disc ratio are assessed for indications of specific pathology
• Retinal vessels (arteries and veins) have different thicknesses. The ratio (A/V) is generally 2:3
• Macula, the central area of the fundus with cone photoreceptors, is darker and thicker than other sections

Direct Ophthalmoscopy

• Provides a view of the posterior pole, macular region, optic nerve, and vascular arcades
• Less demanding to perform compared to other methods
• Magnification ranges up to about 15x

Binocular Indirect Ophthalmoscopy (BIO)

• Head-borne device using an illumination system and oculars
• Used to examine all the areas of the fundus with a panoramic and stereoscopic view
• Advantages: provides stereoscopic view, wider field of view, high contrast, excellent depth of focus, independent of refractive errors, variety of lens options, relatively short examination time
• Disadvantages: inverted and reversed image, low magnification, dilation required, more difficult to perform