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B . Optometry
Slit lamp Biomicroscopy
Biomicroscope derives its name from the
fact that it enables the practitioner to
observe the living tissue of eye under
It not only provides magnified view of every
part of eye but also allows quantitative
measurements and photography of every
part for documentation.
• The lamp facilitates an examination
which looks at anterior segment, or
frontal structures, of the human eye,
which includes the
–Natural crystalline lens and
Important historical landmarks
De Wecker 1863 devised a portable
Albert and Greenough 1891,developed
a binocular microscope which provided
Gullstrand ,1911 introduced the
illumination system which had for the
first time a slit diapharm in it
Therefore Gullstrand is credited with
the invention of slit lamp.
There are 2 types of slit lamp
1)Zeiss slit lamp biomicroscope
2)Haag streit slit lamp biomicroscope
In Zeiss type light source is at the base of
the instrument while in Haag streit type it is
at the top of the instrument.
A "slit" beam of very bright light
produced by lamp. This beam is focused
on to the eye which is then viewed
under magnification with a microscope
Operational components of slit lamp
biomicroscope essentially consist of:
It consist of:
A bright ,focal source of light with a slit
Provides an illumination of 2*10^5 to 4*10^5
The beam of light can be changed in
intensity,height,width,direction or angle and
color during the examination with the flick of
Condensing lens system:
Consist of a couple of planoconvex
lenses with their convex surface in
Slit and other diapharm:
Height and width of slit can be varied by
Form an image of slit at eye.
1.keeps the aberration of lens down.
2.increase the depth of focus of slit.
Reflecting mirrors and prisms
Yellow barrier filter
Red free filter
Neutral density filter
Cobalt blue filter
Observation system is essentially a compound
microscope composed of two optical elements
1.an objective ,2.an eyepiece
It presents to the observer an enlarged image of
a near object.
The objective lens consists of two planoconvex
lenses with their convexities put together
providing a composite power of +22D.
Microscope is binocular i.e. it has two
eyepieces giving binocular observer a
The eye piece has a lens of +10D.
To overcome the problem of inverted
image produced by compound
microscope ,slit lamp microscope uses a
pair of prisms b/w the objective and
eyepiece to reinvert the image.
Most slit lamp provide a range of
magnification from 6x to 40x
Movement of microscope and illumination
system towards and away from the eye
and from side and side is achieved via
Up and down movement arrangement
Obtained via some sort or screw
Patient support arrangement
Vertically movable chin rest and the
A movable fixation target greatly faciliates
the examination under some conditions.
Mechanical coupling :
Provides a coupling of microscope and
the illumination system along a common
axis of rotation that coincides their focal
This ensures that light falls on the point
where the microscope is focused
Has advantages when using the slit lamp
for routine examination of anterior
Magnification control :
Including two or pair of readily
changeable objective lenses and two
sets of eyepieces.
An on and off switch and illumination
Topcon slit lamp model SL-3E
Light beam is controlled by
Joy stick arrangement
may be changed
flipping a lever...
Changing filters. biomicroscope
Filters used in slit lamp biomicroscopy
Cobalt blue filter
Used in conjunction with fluorescein stain
Dye pods in area where the corneal epithelium
is broken or absent.
The dye absorbs blue light and emits green.
RGP lenses fitting
Obscure any thing that is red hence
the red free light , thus blood vessels
or haemorrhages appears black.
This increases contrast ,revealing the
path and pattern of inflammed blood
Fleischer ring can also be viewed
satisfactorily with the red green filter.
Angle between microscope and
illumination system should be 30-45
Slit width should be widest.
Filter to be used is diffusing filter.
Magnification: low to medium
Illumination: medium to high.
General view of anterior of eye:
lids,lashes,sclera,cornea ,iris, pupil,
Gross pathology and media opacities
Contact lens fitting.
Assessment of lachrymal reflex.
Optics of diffuse illumination Diffuse illumination with slit beam and
Involves placing the light source at an
angle of about 40-50 degree from
This arrangement permits both light beam
and microscope to be sharply focused on
the ocular tissue being observed.
Wide beam direct illumination is commonly
used as a preliminary technique to
evaluate large area.
it is particularly suitable for assessment
of cataracts,scars,nerves,vessels etc.
It is also of great importance for the
determination of stabilization of axis of
toric contact lens.
Constructed by narrowing the beam to 1-
2mm in width to illuminate a rectangular
area of cornea.
Microscope is placed directly in front of
Light source is approximately 45 degree
from straight ahead position.
Used to detect and examine corneal
structures and defects.
Used to detect corneal striae that
develop when corneal edema occurs
with hydrogel lens wear and in
Higher magnification than that used with
wide beam illumination is preferred to
evaluate both depth and extent of
corneal ,scarring or foreign bodies.
Produced by narrowing the vertical height of a
parallelepiped to produce a small circular or
square spot of light.
Light source is 45-60 degree temporally and
directed into pupil.
Biomicroscope: directly in front of eye.
Intensity of light source to heighest setting.
Beam is focused between cornea and
anterior lens surface and dark zone
between cornea and anterior lens
Principle is same as that of beam of sun
light streaming through a room
,illuminating airborne dust particles.
This occurance is called tyndall
Most useful when examining the
Cells, pigment or proteins in the
aqueous humour reflect the light like a
To visualise this the slit illuminator is
adjusted to the smallest circular beam
and is projected through the anterior
chamber from a 42° to 90° angle.
The strongest reflection is possible at
Optic section is a very thin parallelepiped and
optically cuts a very thin slice of the cornea.
Axes of illuminating and viewing path intersect
in the area of anterior eye media to be
examined e.g. the individual corneal layers.
Angle between illuminating and viewing path
is 45 degree.
Slit length should be kept small to minimize
dazzling the patient.
With narrow slit the depth and portion of
different objects(penetration depth of
foreign bodies, shape of lens etc) can be
resolved more easily.
With wider slit their extension and shape
are visible more clearly.
Examination of AC depth is performed by
wider slit width .1-.3mm .
Used to localize:
Optical section of lens
1.Corneal scar with wide beam illumination 2.optical section through scar
indicating scar is with in superficial layer of cornea.
Requires that the illumination arm and the
viewing arm be separated by 90 degree.
Medium –wide beam of moderate height is
Microscope is pointing straight ahead.
Magnification of 10x,16x,or 25x are used.
Anterior and posterior cornea
Iris is best viewed without dilation by
Anterior lens (especially useful for
Established by separating the microscope and
slit beam by equal angles from normal to cornea.
Position of illuminator about 30 degree to one
side and the microscope 30 degree to otherside.
Angle of illuminator to microscope must be equal
Angle of light should be moved until a very bright
reflex obtained from corneal surface which is
called zone of specular reflection.
Irregularities ,deposits ,or excavasation in these
smooth surface will fail to reflect light and these
appears darker than surrounding.
Under specular reflection anterior corneal
surface appears as white uniform surface and
corneal endothelium takes on a mosaic pattern.
Used to observe:
Evaluate general appearance of corneal
Schematic of specularreflection.
front surface endothelium
The beam is focused in an area adjacent to
ocular tissue to be observed.
Examination of objects in direct vicinity of
corneal areas of reduced transparency e,g,
infiltrates,corneal scars,deposits,epithelial and
Narrow to medium slit beam
Magnification: approx. m=12x (depending upon
Formed by reflecting light of slit beam from
a structure more posterior than the
structure under observation.
A vertical slit beam 1-4mm wide can be
Place object of regard against a bright
background allowing object to appear
dark or black.
Used most often in searching for keratic
precipitates and other debris on corneal
The crystalline lens can also be
retroilluminated for viewing of water
clefts and vacuoles of anterior lens and
posterior subcapsular cataract
Direct retroillumination from iris:
Used to view corneal pathology.
A moderately wide slit beam is aimed
towards the iris directly behind the
Use magnification of 16x to 25x and
direct the light from 45 degree.
Microscope is directed straight ahead .
direct retroillumination from
direct retroillumination from the iris.
Indirect retroillumination from iris:
Performed as with direct
retroillumination but the beam is
directed to an area of the iris bordering
the portion of iris behind pathology.
It provides dark background allowing
corneal opacities to be viewed with
Retroillumination from fundus(red
The slit illuminator is positioned in an
almost coaxial position with the
A wide slit beam is decentered and
adjusted to a half circle by using the slit
The decentred slit beam is projected near
the pupil margin through a dilated pupil.
retroillumination from the
Example of retroillumination from the reti
It is formed by focusing a bright but narrow slit
beam on the limbus and using microscope on
Such an illumination technique causes cornea
to take on total internal reflection.
The slit beam should be placed approximately
40-60 degree from the microscope.
When properly positioned this technique will
produce halo glow of light around the limbus
as the light is transmitted around the cornea.
Corneal changes or abnormalities can be
visualized by reflecting the scattered light.
Used to observe:
Central corneal epithelial edema
Corneal nebulae and maculae.
sclerotic scatter. Example of
This illumination technique is used to
observe internal detail, depth, and
Use a short,fairly narrow slit beam.
Place the beam at the border of the
structure or pathology.
The light will be scattered into the
surrounding tissue, creating a light
background that highlights the edges of
Depending on the density of the
abnormality, the light from behind may
reflect through, allowing detailed
examination of the internal structure of
Observe: corneal opacities (edema,
infiltrates, vessels, foreign bodies), lens,
In transillumination, a structure (in the
eye, the iris) is evaluated by how light
passes through it.
This technique also takes advantage of
the red reflex.
The pupil must be at mid mydriasis (3to
4 mm when light stimulated).
Place the light source coaxial (directly
in line) with the microscope.
Use a full circle beam of light equal to
the size of the pupil.
Project the light through the pupil and
into the eye .
Focus the microscope on the iris.
Magnification of 10X to 16X is adequate
Normally the iris pigment absorbs the
light, but pigmentation defects let the red
fundus light pass through..
Observe: iris defects (they will glow with
the orange light reflected from the
Basic slit lamp examination
Head support unit
Adjust height of table or chair
Adjust height of chin rest such that
patients lateral canthus is aligned with
Adjust ocular eyepieces.
Magnification : begin with 6x -10x
Protocol and documentation
Uses of slit lamp biomicroscopy
Anterior segment and posterior
Anterior and posterior segment disease
Lids and lashes
Conjunctiva and cornea
Instillation of fluorescein and BUT
Eversion of the lids
Anterior chamber and angle measurement
Evertion of lids
This technique is used to examine the
inferior and superior palpebral
conjunctiva, particularly in contact lens
wear and when looking for allergic
conjunctival changes, papillae, and
1. Ask the patient to look down and
grasp the superior eyelashes.
2. Press gently on the superior margin of
the tarsal plate using a cotton swab (or
the index finger of the other hand), and
at the same time pull the eyelashes
3. To evert the lower eyelid, pull the
eyelid down and press under the eyelid
margin while moving finger upwards.
The eyelid will evert over finger.
Meibomian gland evaluation
With the patient at the biomicroscope, use
white light and medium magnification to
inspect the lower eyelid margins.
Look for capping of the meibomian gland
orifices (yellow mounds), notching of the
eyelid margins (indentations) and frothing of
the tears on the eyelid margins.
Pull the lower eyelid down and look for
concretions in the palpebral conjunctiva.
With mild pressure, press on the eyelid
margins near the eyelashes and watch
the meibomian gland orifices.
Clear fluid should be expressed.
Capping of the orifices, a cheesy
secretion on expression and frothing of
the eyelid margins indicates meibomian
CENTRAL RETINA PHOTOGRAPHS
WITH A 90-DIOPTER LENS
A moderate slit
beam in the
the best results.
Clinical procedure in optometry
Primary care optometry
Borishs clinical refraction
Theory and practice of optics and refraction:AK