Instrumentation and
investigative techniques
Slit lamp Biomicroscopy
What is slit lamp
• is an instrument consisting of a high-intensity light source
that can be focused to shine a thin sheet of light into the
eye.
• Operational components consists of a binocular
microscope and a light source
• provides light in the form of slit to observe various ocular
structures
• The lamp facilitates an examination of the anterior
segment and posterior segment of the human eye
Optical Principle
• Two systems- illumination and observation
• Mounted on a movable trolley about a common center and
vertical axis
• Works on the same principle of compound microscope
• A narrow "slit" beam of very bright light by lamp. This beam
is focused on to the eye which is then viewed under
magnification with microscope
Types based on illumination system
1. Zeiss slit lamp biomicroscope: Light source at
the bottom
Types based on illumination system
2. Haag streit slit lamp biomicroscope: Light
source at the top
Parts of slit lamp
Mechanical support Observation system
• Forehead rest • Binocular eyepieces
• Chin rest • Camera/video adapter
• Fixation target • Observation tube
• Power supply unit • Magnification Changer
• Locking controls
• Joystick
Mechanical Support
Illumination System
Typical slit
lamp
illumination
system
Illumination System
• Light source-halogen, xenon, W lamps (200000- 400000
lux)
• Condenser Lens system- 2 planoconvex lens: renders a
divergent beam from a point source into a parallel or
converging beam to illuminate an object
• Slit and other diaphragms-stenopaic slits: the slit is oriented
at different angles, changing the retinal blur size
• Filters (Neutral density filter, cobalt blue, red free filter)
• Projection lens- small diameter
• Reflecting mirror/prism
Filters
• Neutral-density filter: reduces or modifies the intensity of all
wavelengths, or colors, of light equally, giving no changes in hue of color
rendition. It can be a colorless (clear) or grey filter. (Reduce beam
brightness and increase comfort for the patient)
• Green (red free) filters: Increase contrast when looking for
corneal and increase the visibility
• Polarizing filters: reduce unwanted specular reflection and
enhance visibility of subtle defects
• Cobalt blue filters: Slit lamps produce light of the wavelength
450 to 500 nm, known as "cobalt blue". This light is specifically useful for
looking for problems in the eye once it has been stained with fluorescein
•
Illumination types
1. Diffuse illumination:
² light is spread evenly over the entire observed
surface
² 45 degree angle and fully open slit
² If no ND filter (diffuser), decreasing intensity
² Least amount of magnification (6x or 10x)
² The cobalt blue and red –free filters also act as
diffuser, but white light is generally used
Illumination types
2. Direct Illumination:
² Observation and illumination system focus
at the same point
² Vary angle of illumination
² Variable magnification
² Variable width and height of light
Illumination types
3. Indirect Illumination:
² Observation and illumination system are
not focused at the same point
² Beam is focused on an area adjacent to the
area to be observed
² Vary angle of illumination
² Low to high magnification
Illumination types
4. Retro Illumination:
² Object of regard is illuminated by reflected
light
² Reflected light from iris
² Vary angle of illumination
² Medium to high magnification
Illumination types
5. Tangential Illumination
² Angle between the slit and
microscope 70 – 80 deg
² Used to see iris freckles
and tumors, general integrity of cornea
and iris
