Slit lamp biomicroscopy

We are forever indebted to Allavar Gullstrand,
who won the Nobel prize in physiology or
medicine in 1911 for his works on the dioptrics of
the eye. It was he who first gave the concept of a
slit lamp.
The word slit lamp is a misnomer as a slit is only
one of the many diaphragms of the instrument.
Hence the term “biomicroscopy” was introduced.

The most important advantage of slit lamp is
the 3 dimensional view of the ocular
structures.
The 3 prerequisites for this 3d view are
-Stereopsis (which is provided by
the binocular microscope)
-Direction of the light beam (which
can be changed)
-The shape of the light beam (which
can be changed)

PARTS OF THE SLIT LAMP
1.The observation system
2. The illumination system
3. The mechanical system

ILLUMINATION SYSTEM
Haag streit type- with vertical
decoupling.
Zeiss type- with no vertical
decoupling.

HALOGEN BULB
CONDENSING LENS
SLIT APERTURE
LENS
TILTED MIRROR
EYE
The light is controlled by a
transformer and can be changed in
intensity, height, width, direction,
angle and colour.

OBSERVATION SYSTEM
Magnifications available are 5x 16x 25x 40x and in some
100x.
Resolution is more important than magnification. This is
provided by the short wave length light of the halogen
bulb.
The resolution of a slit-lamp is dependent on the
wavelength of light used, the refractive index between the
eye and objective, the working distance, and the diameter
of the objective lens.

MECHANICAL SYSTEM
The slit lamp is mounted on a stage designed for movement
of microscope and patient positioning. The joystick controls
the microscope position.

PRE EXAMINATION:
1.PATIENT POSITION:
The slit lamp should be locked in the farthest away position
when the patient sits to ensure safety
Explain the procedure to the patient. Ask him to
keep both eyes open and that he can blink his eyes.
Adjust the height and distance of the table or chair.
Patients back should be straight and neck aligned with back.
He should lean forwards at the hips.
The head should be such that the lateral canthus lies at the
mark on the headbar.
Ask the patient to grasp the handle.
Children may stand or sit on their parents lap.

Adjust the ocular eyepieces according to the examiner’s
refractive error and inter pupillary distance.
Fixation: ask the patient to fixate on a distant target or light
or the observer’s ear with the other eye.
Magnification: Start from the least and increase as needed.
Focussing: Start with the stage all the way forward, you know
that the only possible motion in order to focus is to pull
back. Move the stage back slowly with the joystick until the
eye is focused. you can look at the beam on the patient’s eye
from the side of the instrument.

ILLUMINATION TECHNIQUES:
1. DIFFUSE ILLUMINATION-
IS USED FOR GROSS SURVEY OF
THE EYE. AFTER LOOKING FOR
GROSS PATHOLOGY THE
INTERESTED AREA CAN BE
FOCUSSED.
• LIGHT AT 45 DEGREES
• MICROSCOPE STRAIGHT
• LEAST ILLUMINATION/
DIFFUSER/ NEUTRAL DENSITY
FILTER/ BLUE/GREEN FILTER.
• LEAST MAGNIFICATION.
• FULL WIDTH BEAM.

2. DIRECT IILLUMINATION
A) BEAM/NARROW BEAM:
USES A 0.5-1MM SLIT
HIGH ILLUMINATION
LOW OR MEDIUM
MAGNIFICATION.
• TO SEE CORNEAL THICKNESS,
SHAPE, BULLAE, DELLEN
• SITE OF FOREIGN BODY
• OPACITIES, SCARSS
• DEPTH OF AC
• LOCATION OF CATARACT

B) CONICAL/ PIN POINT
TO SEE AC FOR CELLS AND FLARE
• HIGH MAGNIFICATION (16X)
• HIGH ILLUMINNATION
• MICROSCOPE STRAIGHT AHEAD
• LIGHT 45 TO 60 DEGREES.
FLARE IS DUE TO PROTEINS HENCE
APPEARS GREY / MILKY
CELLS REFLECT LIGHT AND HENCE
APPEAR AS WHITE DOTS.
SEEN DUE TO TYNDALL EFFECT.

TYNDALL EFFECT Light scattering by particles in a
colloid or suspension.

C) BROAD BEAM/ TANGENTIAL/
PARALLELIPIPED
GIVES A 3 DIMENTIONAL VIEW OF
CORNEA DUE TO SHADOWS.
• 2-4MM SLIT
• LIGHT AT 45 DEGREES
As the beam sweeps the cornea, it
enhances surface irregularities by
creating shadows.
TO SEE TEAR DEBRIS
CORNEAL NERVES AND VESSELS
CORNEAL OPACITIES
STRIAE OR DM FOLDS
KRUKENBERG SPINDLES

D) SPECULAR REFLECTION
This technique is used to view the endothelium.
Specular reflection is achieved by positioning the beam of light
and microscope in such a position so that the angle of
incidence is equal to the angle of reflection.
This method is monocular.
In this technique, position the illuminator about 30 degrees to
one side and the microscope 30 degrees to the other side. The
angle of the illuminator to the microscope must be equal and
opposite.

A parallelepiped is used for specular reflection.
The focus is moved back toward the endothelial cells. There will be
a point where two images are seen, one bright, and the other
ghost-like or copper-yellow in color.
Then move the light a little to the side, and look adjacent to it, at
the reflection from the endothelial surface. Now switch to the
highest magnification available.
When the biomicroscope is focused on the ghost-like filament a
mosaic of hexagonal cells are seen.
Can be used to see anterior and posterior lens capsule too.

3) INDIRECT ILLUMINATION:
A) PROXIMAL ILLUMINATION:
Use a parallelepiped beam sharply
focused on a given structure like the
cornea. The light passes through the
cornea and falls out of focus on the
iris. The dark area just lateral or
proximal to the parallelepiped is the
indirect or proximal zone of
illumination.

B) RETROILLUMINATION:
The light is reflected off the deeper structures, such as
the iris or retina, while the microscope is focused to
study the more anterior structures in the reflected light.
IRIS RETROILLUMINATION:
DIRECT- to view cornea
INDIRECT- to view cornea (and angles)
RETROILLUMINATION FROM RETINA: to see the lens
and cornea.

Direct iris retroilllumination Indirect iris
retroillumination
Light beam hits iris behind
the pathology.
Illuminates cornea from
behind.
Accentuates the refractive
properties of the cornea.
Against a light background.
Decentered beam hits the
iris adjacent to the corneal
pathology.
Illuminates cornea from
behind
Against a dark
background.

Direct iris retroilllumination
Indirect iris
retroillumination

Direct
retroillumination
Indirect
retroillumination

Retroillumination from the fundus:
Slit beam is placed
nearly coaxial with
microscope and
rotated slightly off
axis.
This allows the red
light reflected from
the fundus to pass
through thee lens and
cornea.

Direct iris
retroillumination
Indirect iris
retroillumination
Retroillumination
from fundus

TRANSILLUMINATION FROM IRIS
In transillumination, the
iris is evaluated by how
light passes through it.
This technique also takes
advantage of the red
reflex.
It helps to see defects in
the iris.

SCLEROTIC SCATTER:
The optical principle is same as that of fibre optics-
total internal reflection of light.
The slit beam is directed at the limbus from where the
sclera scatters the light. Some of this enters the corneal
stroma and travels the entire cornea getting internally
reflected.
An opacity causes light to scatter and be visualised by
the examiner.

•This is such as to make the system “parfocal”
•i.e the focus of the slit and the focus of the microscope
are at the same point.
•This parfocality may occasionally need to be dissociated
as for example in the technique of sclerotic scatter.
The coupling between the slit lamp and the
biomicroscope
•This allows both the slit and the microscope to rotate
about the point of focus (i.ethe eye)
Dissociation of parfocality can be done in “Haag Streit”
type slit lamps by loosening the sclerotic scatter knob
The coupling between the slit lamp
and the biomicroscope

FILTERS IN A SLIT LAMP:
1) COBALT BLUE FILTER:
The cobalt blue filter is used in
conjunction with fluorescein
dye. The dye pools in areas
where the corneal epithelium
is broken or absent. The blue
light excites the fluorescein,
which then takes on a
yellowish glow.

2) GREEN FILTER (RED FREE FILTER):
• The green filter obscures anything that is
red.Thus, blood vessels or hemorrhages
appear black. This increases contrast,
revealing the path and pattern of inflamed
blood vessels.
• Areas of the episclera where lymphocytes
have gathered in response to an
inflammatory or immune response will
appear as yellow spots under the red-free
light.
• Fleischer ring can also be viewed
satisfactorily with the red-free filter.

3) DIFFUSER:
Some instruments have a diffuser, which is a piece
of frosted glass or plastic that flips in front of the
illuminator. The diffuser scatters the light, causing
an even spread of light over the entire ocular
surface.

ATTACHMENTS:
1. GAT
2. PACHYMETRY
3. GONIOSCOPY
4. HRUBY LENS
5. DIGITAL CAMERA.

Slit lamp biomicroscopy

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Slit lamp biomicroscopy