Day 6 (2): Slit-Lamp Biomicroscopy Flashcards
What is a Slit Lamp Biomicroscope
- Stereoscopic biomicroscope that emits a focused beam of light with variable height, width, and angle.
- Gold standard in 3D visualization and measurement of the fine anatomy of the adnexa and anterior segment
- Using hand-held lenses, posterior segment may be visualized as well
- Advantages:
1. excellent image quality
2. stereoscopic image (depth perception due to binocularity)
3. adjustable illumination and magnification
Indications for use of the slit-lamp.
- Examination of the anterior eye segment (adnexa to the anterior vitreous): most common indication
- Contact lens fitting
Other tests that can be performed in tandem with slit lamp examination.
- Gonioscopy: to visualize iridocorneal angle
- Fundoscopy: to visualize posterior segment
- Ocular photography
- Goldmann applanation tonometry
- Laser photocoagulation
- Test for ocular surface assessment (Schirmer’s, Fluorescein tests)
Four main parts of a slit-lamp biomicroscope
- Base
- Patient Support Frame
- Illumination Arm (on swivel): the slit-lamp part
- Viewing Arm (on swivel): the biomicroscope part
What are the parts of the slit lamp base?
- Adjustable table
- Power switch
- Intensity rheostat
- Locking carriage (for coarse X-Y plane)
- Joystick (for fine X-Y, as well as Z)
What are the parts of the patient support frame?
- Forehead band
- Chin rest
- Chin height adjustment knob
- Patient handles
- Canthus height indicator
What are the parts of the Illumination Arm?
- Light source
- Illumination filters
- Beam height adjustment
- Slit illuminator
- Beam width adjustment
- Center screw
- To change slit size and shape, filters/light color and brightness
What are the parts of the Viewing Arm?
- Oculars/eyepieces with adjustable focus
2. Magnification control knob
Describe the relationship between the illumination arm and the viewing arm.
- COPIVOTAL: mechanically coupled around a central pivot point
- PARFOCAL: convergence point of the light beam coincides with the focal point of the microscope.
- ISOCENTRIC: always central regardless of angle
- Both can swing independently 180 degrees along the horizontal
Two basic models of the slit lamp biomicroscope?
Haag-Streit Type
Zeiss Type
Characteristics of a good SLB?
- Adequate working distance between microscope and eye
- Adaptable to different users
- Good resolution
- Good depth of image
- Wide range of magnifications
- Wide breath shield
What are the different magnifications available in the SLB?
- Wide range of available magnifications
- Lower: general assessment and orientation
- Higher: detailed inspections of areas of interest
- Methods:
1. Littmann-Galilean telescope: most common
2. Zoom Systems: high-end models (7x - 40x)
3. Changing eyepieces or objective lenses: obsolete
What are the different parameters of the slit light?
- Width: 0 - 14 mm
- light source starts out as round and slit can be adjusted to become rectangular
- graduated for measurements
- narrow: slices through cornea to determine depth or thickness
- wide: inspect surfaces - Height: adjustable or fixed
- graduated for measurements
- long: structures in anterior to pupil
- short: passes into pupil to view structures posterior to pupil; assess clarity of anterior chamber (cells and flare) - Orientation: rotate lamp housing
- Filters
- Diffuser
- Polarizing
- Red-free
- Cobalt blue
- Wratten: for contact lens fitting
What are the different methods of illumination and views that can be done with a SLB?
- Direct Illumination
- Indirect Illumination
- Retro-Illumination (Iris or Fundus)
- Sclerotic Scatter
- Specular View (Specular Microscopy)
What is Direct Illumination?
- Both light source and microscope are pointed at the object of interest
- Slit width determines the parts of the eye visualized
- Classified according to the width of the slit:
1. Diffuse Beam: general inspection of the eye
2. Wide Beam: broad view of the surface
3. Parallelepiped Beam - Wide: broad view of the surface
- Narrow: balanced view of surface with depth
4. Optical Section: cut section for thickness and depth
What is the importance of the angle between the viewing arm and the illumination arm?
- Graduated scale is located at the pivot point of the two arms
- As the angle between the two arms increases, depth is better assessed and less of the surface is seen.
- 5 degrees: surface only
- 45 degrees: balanced view (surface + depth)
- 85 degrees: depth/thickness only
Wider angles
- visualize deeper layers without interference from reflection of anterior layers
- assess depth or thickness
- assess texture or smoothness or corneal surface
- wider the beam = greater the angle needed to see posterior layers
What is the Diffuse beam or Wide beam used for?
- General inspection of the eye and adnexa
- Color assessment of the iris
- Contact lens fitting
- Disadvantage: brightness is poorly tolerated
- Settings:
1. Wide slit
2. Diffusing filter
3. Angle: 30-50 degrees
4. Magnification: 6-10X
What is the Parallelepiped beam used for?
- Default method for corneal inspection
- Block of tissue is displayed in 3D showing a balanced view with both surface characteristics and depth
- Settings:
1. Slit: 2 mm
2. Angle: 30-50 degrees
4. Magnification: 10-25X
What is the Optical Section used for?
- Detailed assessment of depth and thickness
- Surface characteristics not in view
- Settings:
1. High illumination in a dark room
2. Narrowest slit: 0.1 - 0.2 mm
3. Angle: largest possible (80-90 degrees)
4. Magnification: 10-25X - Structures seen:
1. Corneal layers
2. Anterior chamber
3. Iris
What is Indirect Illumination?
- Target structure is illuminated indirectly by reflections or scattered light from an object to which the light source is directed to
- Light is internally reflected within the cornea or reflected by surrounding tissues
- Similar to how the light given off by the moon is just a reflection of the light from the sun
- Indications:
1. Subtle findings: obscured by intense illumination
2. Opacities: scatter light so best viewed against a dark background - Settings: BRIGHT object, DARK background
1. Medium slit: 2 - 4 mm
2. Angle: medium to wide (30 - 50 degrees)
3. Magnification: medium to high if subtle
What is Retro-Illumination?
Appearance: DARK object, BRIGHT background
- best for assessing keratic precipitates on the posterior surface of the cornea
Iris Retro-Illumination: illuminates cornea
- Narrow to moderate width and LONG slit
- Angle: wide (80 - 90 degrees)
- if high magnification warranted: may need to remove parfocality by decoupling viewing and illumination arms - Magnification: depending on target object size
Fundus Retro-Illumination: illuminates cornea and lens
- pupil dilation is warranted
1. Narrow to moderate width and SHORT slit (to fit into pupil)
2. Angle: narrow (0 - 10 degrees) because target is pupil
3. Magnification: moderate
What is Sclerotic Scatter view?
Principle: total internal reflection of light through the cornea
Target: lesions in the corneal stroma
- Intense illumination
- Arms are decoupled:
- Viewing Arm: center of cornea
- Illumination Arm: 45 degrees from center directed into the limbus - Magnification: depending on target object size
What is Specular Reflection or Specular Microscopy?
Assessment of the corneal endothelium
- Cell density
- Cell size variation (polymegathism)
- Cell shape variation (pleomorphism)
Settings:
- Medium slit
- Angle: wide (80 - 90 degrees)
- Magnification: high
What slit width and length is used to view anterior chamber reactions (cells and flare)?
Narrow and short slit