The slit lamp biomicroscope allows examination of the anterior segment of the eye at high magnification. It consists of an illumination system using a bright slit of light and an observation system using a binocular microscope. Different illumination techniques such as diffuse, direct, and retroillumination can be used to examine different structures. The slit lamp provides important information for diagnosing eye diseases and has been improved since its invention over 100 years ago to include features like variable magnification and filters. It remains a vital tool for comprehensive eye examinations.

1. MANOJ ARYAL
B . Optometry
IOM,MMC
Slit lamp Biomicroscopy
(Instrumentation,Principle, Illumination
and Uses)
optometris
t

2. Introduction
 Biomicroscope derives its name from the
fact that it enables the practitioner to
observe the living tissue of eye under
magnification.
 It not only provides magnified view of every
part of eye but also allows quantitative
measurements and photography of every
part for documentation.

3. • The lamp facilitates an examination
which looks at anterior segment, or
frontal structures, of the human eye,
which includes the
–Eyelid
–Cornea
–Sclera
–Conjunctiva
–Iris
–Aqueous
–Natural crystalline lens and
–Anterior vitreous.

4. Important historical landmarks
 De Wecker 1863 devised a portable
ophthalmomicroscope .
 Albert and Greenough 1891,developed
a binocular microscope which provided
stereoscopic view.
 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.

5. Large Gullstrand
Ophthalmomicroscop
e (1911)

6. TYPES
 There are 2 types of slit lamp
biomicroscope
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.

7. Zeiss slit lamp biomicroscope
Haag streit slit lamp biomicroscope

8. PRINCIPLE
 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

10. Instrumentation
 Operational components of slit lamp
biomicroscope essentially consist of:
Illumination system
Observation system
Mechanical system

11.  Illumination system
 It consist of:
A bright ,focal source of light with a slit
mechanism
 Provides an illumination of 2*10^5 to 4*10^5
lux.
 The beam of light can be changed in
intensity,height,width,direction or angle and
color during the examination with the flick of
lever.

12. Condensing lens system:
Consist of a couple of planoconvex
lenses with their convex surface in
apposition.
Slit and other diapharm:
 Height and width of slit can be varied by
using knobs.

13.  Projection lens:
 Form an image of slit at eye.
 Advantages,
 1.keeps the aberration of lens down.
 2.increase the depth of focus of slit.

14.  Reflecting mirrors and prisms
 Filters
Yellow barrier filter
Red free filter
Neutral density filter
Cobalt blue filter
diffuser

15. Observation system(microscope)
 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

16.  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

17. Mechanical system
 Joystick arrangement
 Movement of microscope and illumination
system towards and away from the eye
and from side and side is achieved via
joystick arrangement.
Up and down movement arrangement
Obtained via some sort or screw
devices.
Patient support arrangement
Vertically movable chin rest and the

18. Fixation target:
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
planes.
 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

19.  Magnification control :
Including two or pair of readily
changeable objective lenses and two
sets of eyepieces.
 An on and off switch and illumination
control .

20. Topcon slit lamp model SL-3E
Light beam is controlled by
knobs
Joy stick arrangement
Chin rest
Reflecting mirror
biomicroscope
Illumination control

21. Magnification
may be changed
by
flipping a lever...
Changing filters. biomicroscope
Patient positioning
Alignmen
t mark
Microscope
and light
source rotate
indepedently

22. 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.
 Uses:
 Ocular staining
 RGP lenses fitting
 Tear layer

23.  Red free(green)filter:
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
vessels.
Fleischer ring can also be viewed
satisfactorily with the red green filter.

25. Illumination techniques
 Includes
 Diffuse illumination
 Direct illumination
 Parallilepiped
 Optic section
 Conical(pinpoint)
 Tangential
 Specular reflection
 Indirect illumination
 Retro-illumination
 Sclerotic scatter
 Transillumination
 Proximal illumination

26. Diffuse illumination
 Angle between microscope and
illumination system should be 30-45
degree.
 Slit width should be widest.
 Filter to be used is diffusing filter.
 Magnification: low to medium
 Illumination: medium to high.

27. Applications:
General view of anterior of eye:
lids,lashes,sclera,cornea ,iris, pupil,
Gross pathology and media opacities
Contact lens fitting.
Assessment of lachrymal reflex.

28. Optics of diffuse illumination Diffuse illumination with slit beam and
background illumination

29. Direct illumination
 Involves placing the light source at an
angle of about 40-50 degree from
microscope.
 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.

30.  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.

31.  Parallelepiped:
Constructed by narrowing the beam to 1-
2mm in width to illuminate a rectangular
area of cornea.
Microscope is placed directly in front of
patients cornea.
Light source is approximately 45 degree
from straight ahead position.

32. Applications:
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
keratoconus.
Higher magnification than that used with
wide beam illumination is preferred to
evaluate both depth and extent of
corneal ,scarring or foreign bodies.

34. Conical beam(pinpoint)
 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.
 Magnification: high(16-25x)
 Intensity of light source to heighest setting.

35.  Focusing:
Beam is focused between cornea and
anterior lens surface and dark zone
between cornea and anterior lens
observed.
Principle is same as that of beam of sun
light streaming through a room
,illuminating airborne dust particles.
This occurance is called tyndall
phenomenon.
 Most useful when examining the

36. Tyndall phenomenon
 Cells, pigment or proteins in the
aqueous humour reflect the light like a
faint fog.
 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
90°.

38. Optic section
 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.

39.  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.
 Magnification: maximum.
 Examination of AC depth is performed by
wider slit width .1-.3mm .

40.  Used to localize:
Nerve fibers
Blood vessels
Infiltrates
Cataracts
AC depth.

41. 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.

42. Tangential illumination
 Requires that the illumination arm and the
viewing arm be separated by 90 degree.
 Medium –wide beam of moderate height is
used.
 Microscope is pointing straight ahead.
 Magnification of 10x,16x,or 25x are used.

43.  Observe:
Anterior and posterior cornea
Iris is best viewed without dilation by
this method.
Anterior lens (especially useful for
viewing pseudoexfolation).

44. Example of tangential illumination (iris).

45. Specular reflection
 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
and opposite.
 Angle of light should be moved until a very bright
reflex obtained from corneal surface which is
called zone of specular reflection.

46.  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
endothelium
 Lens surfaces
 Corneal epithelium

47. Schematic of specularreflection.
Reflection from
front surface endothelium

48. Indirect illumination
 The beam is focused in an area adjacent to
ocular tissue to be observed.
 Main application:
 Examination of objects in direct vicinity of
corneal areas of reduced transparency e,g,
infiltrates,corneal scars,deposits,epithelial and
stromal defects
 Illumination:
 Narrow to medium slit beam
 Decentred beam
 Magnification: approx. m=12x (depending upon
object size)

49. Retroillumination
 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
used.
 Purpose:
Place object of regard against a bright
background allowing object to appear
dark or black.

50.  Used most often in searching for keratic
precipitates and other debris on corneal
endothelium.
 The crystalline lens can also be
retroilluminated for viewing of water
clefts and vacuoles of anterior lens and
posterior subcapsular cataract

51.  Direct retroillumination from iris:
Used to view corneal pathology.
A moderately wide slit beam is aimed
towards the iris directly behind the
corneal anomaly.
Use magnification of 16x to 25x and
direct the light from 45 degree.
Microscope is directed straight ahead .

52. Schematic of
direct retroillumination from
the iris.
direct retroillumination from the iris.

53.  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
more contrast.
Observe:
Cornea, angles.

55. Retroillumination from fundus(red
reflex photography)
 The slit illuminator is positioned in an
almost coaxial position with the
biomicroscope.
 A wide slit beam is decentered and
adjusted to a half circle by using the slit
width and
 The decentred slit beam is projected near
the pupil margin through a dilated pupil.

56. Schematic of
retroillumination from the
retina.
Example of retroillumination from the reti

57. Sclerotic scatter
 It is formed by focusing a bright but narrow slit
beam on the limbus and using microscope on
low magnification.
 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.

58.  Used to observe:
Central corneal epithelial edema
Corneal abrasions
Corneal nebulae and maculae.

59. Schematic of
sclerotic scatter. Example of
sclerotic scatter.

60. Proximal illumination
 This illumination technique is used to
observe internal detail, depth, and
density.
 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

61.  Depending on the density of the
abnormality, the light from behind may
reflect through, allowing detailed
examination of the internal structure of
the pathology.
 Observe: corneal opacities (edema,
infiltrates, vessels, foreign bodies), lens,
iris

62. Transillumination
 In transillumination, a structure (in the
eye, the iris) is evaluated by how light
passes through it.
 Iris transillumination:
 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.

63.  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
fundus)

65. Basic slit lamp examination
 Patient positioning:
Head support unit
Adjust height of table or chair
Adjust height of chin rest such that
patients lateral canthus is aligned with
the mark.
Adjust ocular eyepieces.

66. Power up
Fixation
Magnification : begin with 6x -10x
magnification
Focusing
Special procedures
Protocol and documentation

67. Uses of slit lamp biomicroscopy
 Diagnostic:
OCT
FFA
Anterior segment and posterior
segment diseases
Dry eye

68.  Procedures:
 Applanation
 Tear evaluation
 Pachymetry
 Gonioscopy
 Contact lens fitting
 Therapeutic:
 Laser
 FB removal
 epilation

69. Anterior and posterior segment disease
evaluation
 Lids and lashes
 Conjunctiva and cornea
 Instillation of fluorescein and BUT
measurement
 Eversion of the lids
 Anterior chamber and angle measurement
 Iris
 Crystalline lens
 Anterior vitreous

70. Injected conjunctivaMeibomian gland openings
pinquecula,
INSTILLATION OF FLUORESCEIN PALPEBRAL CONJUNCTIVA
EXAMINATION

71. 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
foreign bodies.
 1. Ask the patient to look down and
grasp the superior eyelashes.

72.  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
upwards.
 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.

73. 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.

74.  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
gland dysfunction.

75. CENTRAL RETINA PHOTOGRAPHS
WITH A 90-DIOPTER LENS
 A moderate slit
beam in the
almost coaxial
position gives
the best results.

76. References
 Clinical procedure in optometry
 Primary care optometry
 Borishs clinical refraction
 Theory and practice of optics and refraction:AK
Khurana
 internet