This document provides an overview of slit lamp biomicroscopy. It describes the basic components and design of the slit lamp, including the illumination, observation, and mechanical systems. Various techniques for examining the eye using the slit lamp are covered, such as diffuse illumination, sclerotic scatter, focal slit illumination, and retroillumination from the iris or fundus. A brief history of the development of the slit lamp is also presented.

1. DR.Prashant .P.Patel
Senior resident,
Aravind Eye Hospital, Tirunelveli.

2. Slit lamp Biomicroscopy
• It is a dynamic examination in which eye and
ocular adnexa are scanned anteroposteriorly and
horizontally.
• Slit Lamp: It is a misnomer since slit is only one
of the various other diaphragmatic opening
present in the instrument.
• Slit lamp biomicroscopy:
1) Term introduced by Mawas in 1925.
2) Examination of living eye by means of
microscope and slit lamp.

3. • The slit-lamp is one of the important examination tools of
ophthalmologists.
• One of the most important advantages of slit-lamp examination is that
one can examine the eye structure in three dimensions (3D).
• There are three basic requirements for appreciation of depth with a slit-lamp.
• The first depends upon the clinician possessing a third grade of binocular
vision called stereopsis.
• The second involves the direction of the incoming light source, and is
dependent upon the fact that the light beam can be moved so it comes in
from one side or the other.
• The third involves the shape of the slit.

4. History
• Purkinje: One of the first individuals to apply
microscopy to the living eye , who studied the iris
with an adjustable microscope by illuminating the
field of view.
• Louis de Wecker : He made the uniocular slit-lamp
combined an eyepiece, objective and adjustable
condensing lens within a tube.
• It was improved by Siegfried Czapski who added
binocularity to the microscope.
• However, none of the units had sufficient and
adjustable illumination.

5. • Allvar Gullstrand: An ophthalmologist and
1911 Nobel laureate introduced the illumination
system which had for the first time a slit
diaphragm, therefore Gullstrand is credited
with the invention of the slit lamp.

6. • Henker and Vogt improved upon Gullstrand’s
device in 1911 by creating an adjustable slit-lamp
by combining Czapski’s microscope with
Gullstrand’s slit-lamp illumination.

7. Basic design of slit lamp
• The three main components of the modern
slit-lamp are:
1) Illumination system
2)Observation system
3) Mechanical system

8. Mechanical system
• It is mainly concerned with:
• Positioning of patient.
• Adjustment for observer and patient.
• Adjustment of illumination and observations
system.
• It generally contains following hard ware.

9. Fixation light
Head rest
Canthal alignment mark
Chin rest
Lock for slit lamp base
Joy stick
Power unit

10. Chinrest adjust
-ment knob
Height adjustment
switch

11. • Mechanical coupling: Mechanical system
provides coupling of microscope and
illumination system along a common axis of
rotation that coincides their focal planes.
• This arrangement ensures that light falls on
the point where microscope is focused.

12. Illumination System
It is based on Kohler illumination
•The light source L is imaged in the objective O by the collector
system K. The objective in turn produces an image at S in the
mechanical slit located next to the collector system. The image of
the light source at O is the exit pupil of the system.
•The filament is imaged on to the objective lens but the
mechanical slit is imaged on to the patient’s eye.

13. • Köhler illumination provides a very
homogeneous slit image.

14. Illumination System
• The illumination system of most slit-lamps
consists of two different designs.
• The first design: the Haag-Streit type
illumination, allows de-coupling in the vertical
meridian.
• Such vertical de-coupling is particularly useful
when performing gonioscopy to minimize
reflections and for indirect fundus examination to
gain increased peripheral views.

16. In the Zeiss type the illumination comes from below.
The second design: the Zeiss type illumination system, does not allow decoupling in
the vertical meridian.

17. Illumination system control
• Angle
• Width
• Type
1.Neutral density2.Red free
3.Cobalt blue
• Height
• Intensity

18. Observation system
• Should have following Characteristics :
• Optimum stereoscopic observation.
• Selectable magnification.
• Large field of view.
• Large depth of field.
• Enough space in front of the
microscope for manipulations on the
eye.

19. Observation system is composed of
• An objective lens: Two planoconvex lenses with
their convexities put together.
• Magnifying lenses
• Telescope
• Pair of prisms: To reinvert the image.
• Eyepiece
• Converging tubes: They are converged at an
angle of 10-15 degree, to provide good
stereopsis.

20. • The object is located at the object side focal
point of the magnifying lens that magnifies
the object image projecting it virtually to
infinity.
• The image is than viewed with respective
magnification through telescope.

21. Change in magnification
• Grenough type:
• Galilean changer type:
• Czapskiscope with rotating objective:
• Zoom system:

22. The Grenough type(Classical Haag
Streit)
Flip lever to change
magnification

23. • The Galilean Magnification
changer

25. The Galilean Magnification changer
• It utilises the Galilean telescopes to alter the
magnification.
• It has two optical components:
• 1)Positive lens 2)Negative lens
• Lenses are arranged in turret arrangement.
• It provides large range of magnifications,
typically five.

26. The Galilean Magnification changer

27. The Galilean Magnification changer
Knob to change
magnification (3
or 5step)

28. Czapskiscope with rotating objectives
• The different objectives are usually placed on
a turret type of arrangement that allows them
to be fairly rapidly changed during
examination.

29. Zoom System
• Zoom system allows continuously various
degree of magnification.
• E.g, Nikon photo slit lamp &Zeiss-75 Sl

30. Magnification can also be changed
by changing the eyepiece power

31. Clinical Procedure
• Before using the slit-lamp, it is important to
ensure that the instrument is correctly set up.
• The eyepieces should be focused for the observer
for his/her own refractive error.
• Often a little more minus correction is required
than the observer’s actual refractive error due to
accommodation and proximal convergence.
• The Pupillary distance (pd) is adjusted for the
observer (perhaps the pd should be slightly less
than that usually measured to account for
proximal convergence).

32. • Check that the observation and illumination
systems are coupled, and the slit-beam is of
even illumination and has sharply demarcated
edge (otherwise irregularity of the beam may
be falsely interpreted as irregularity of
tissues).
• The slit-lamp examination is conducted in a
semi dark room.

33. • Patient is seated in front of slit-lamp on an
adjustable stool and his/her head is steadied by
placing chin on chin-rest and his forehead rests
on the bar of head-rest.
• Adjust the chin-rest so that the patient’s eyes are
approximately level with the black marker on
the side of the head rest.
• Focus the slit-beam on the eye by moving the
joystick either towards or away from the patient.

34. • The examination should be commenced using the
X10 eyepieces and the lower powered objective
to locate the pathology and higher magnification
should then be used to examine it.
• Use the lowest voltage setting on the
transformer.
• Select the longest slit-length by means of the
appropriate lever.
• The angulation between the observation arm and
the illumination arm is adjusted.

35. Examination methods –
Types of Illumination.
• Slit lamp Provides three basic types of Illuminations.
• 1)Focal Illumination:
Achieved by narrowing the slit horizontally or
vertically, provides isolation of the specific areas of eye
/cornea for observation.
• 2) Oblique illumination: It is essential for detecting and
examining findings in different layers of the cornea.
• 3)The Optical Section: The narrow slit beam slices
through the eye revealing the internal details of the
tissue at all layers.

36. Types of Illumination
• Dffuse Illumination:
Terminology :It is the type encountered in everyday life.
For example light from sun or a light bulb that
diffusely illuminate one’s surroundings.
Principle :It is a Initial survey examination of the face,
eyelids and ocular surface.
If one directly proceeds with the magnified
examination one is likely to miss skin disorders( such
as acne rosacea), eyelid lesions ( such as molluscum
contagiosum, small chalasion, mild ptosis).
Technique: It can be done with torch light ,

37. Diffuse illumination with slit lamp
1)Swing the microscope aside or keep it at 30-
40’ of angle.
2)Opening the slit beam to full height and width.
3)Dialing in the neutral density filter.
• Beam is only 8-14 mm diameter and
therefore must be moved over the eyelids and
ocular surface.
• It can reveal location and general pattern of
eyelid, conjunctival, corneal lesions.

40. Sclerotic Scatter
• Terminology :In this technique for illuminating cornea, the
slit beam is directed at the scleral limbus and illumination
is transmitted into cornea by total internal reflection.
• Opacities within the cornea scatter the light back to the
observer.
• Principle: Opaque sclera scatters the light at the point of
illumination, some of the light is directed in to corneal
stroma, where it travels through the entire cornea by
repeatedly reflecting from its anterior and posterior
surfaces.
• The light emerges around circumference of the cornea,
where it encounters the opaque sclera and create a
glowing halo.

42. • Should be used early in the examination
because,
1) The patient acclimates to bright light of the
slit lamp before it is directed in to the pupil.
2) It accurately reveals the presence and
pattern of corneal opacities.
3) It helps to identify faint opacities that are
difficult to see in direct illumination.

43. • Technique:
• SLIT BEAM : Moderate width, Directed at the
3- or 9-o’clock scleral limbus
• MICROSCOPE: Independently focused onto
the cornea.

45. Direct focal slit illumination
• Terminology : Projection , of a narrow slit beam at an
angle, to the corneal surface, producing an optical section
that slices through the cornea and eye.
• Principle: A direct narrow slit beam optically cuts through
the cornea , providing a cross sectional view that reveals
its contour and its internal structure.
• It forms two parallel curved surface, one that follows
anterior corneal surface and one that posterior corneal
surface.
• Two surfaces are joined by a block of light scattered in the
stroma to create a geometric figure that resembles an
elongated ice cube.
• This is known as parallelepiped/ optical block/optical
section.

46. • Technique:
• Best used after the lesion is located by
sclerotic scatter, diffuse illumination.
• Examiner than focuses narrow slit of light
over this lesion.
• SLIT BEAM: Narrow
• Approximately 30’ angle between slit beam
and microscope, can be increased up to 90’.

50. Broad tangential illumination
• Terminology: A wide beam is oriented at an
extremely oblique illumination angle, causing it
to project tangentially across the corneal surface.
• Principle : Extreme angle of incidence of the slit
beam results in decrease of light reflected and
scattered by the cornea, this in turn reduces
background glare causes surface abnormalities to
stand out.
• It is most useful for examining corneal surface.

52. • Technique:
• SLIT BEAM: wide
• ANGLE between slit beam and microscope:
70-80’.
• This highlights irregularities of corneal
surface such as epithelial defect, PEES etc.

55. Proximal( indirect) illumination
• Terminology: It requires that the slit beam is directed
adjacent (proximal) to the area of interest to illuminate it
indirectly.
• Principle: It combines the Principle of Sclerotic Scatter and
Retro illumination.
• When directed adjacent to opaque area of the cornea, the
illumination of the slit beam is internally reflected within
the cornea causing light to spread throughout the stroma,
light striking the opacity is scattered and some of the
scattered light is reflected back to the observer.
• It is used to define the an opaque area of the cornea and
to identify details within the opacity.

56. • Technique:
• SLIT Beam:
• Short: 2-3 mm
• Slightly broad: 0.2 mm
• Directed adjacent to area of interest.
• Angle between microscope and slit lamp is 15
degree.

59. Retroillumination from Iris
• Terminology: It is a technique of illuminating
an area of cornea using light reflected from
structure posterior to cornea such as iris.
• Direct type: Cornea illuminated by light is
viewed directly.
• Indirect type: Cornea viewed adjacent to area
of illuminated by the reflected light.

60. Direct type of Retro illumination

62. Indirect type of Retro illumination
from Iris

63. • Principle: When light of direct illumination strikes
a corneal opacity, it scatters and some of the light
is reflected back towards the examiner. This form
of illumination often washes out and obscures
details of the lesion and provide little
information about optical qualities and internal
structure of small lesion.
• When retroillumination is used these details
stands out more prominently because the lesion
is less likely to scatter and more likely to obstruct
and refract the reflected light.

64. • Observer looks for three optical phenomena in
retroillumination.
• 1) Obstruction of light by densely opaque
abnormalities appear black against the light
beam. e.g, pigment deposit.
• 2)Substructure of the droplets or refractile
material in retroillumination.
• 3)Distortion of light especially near the edge of
the abnormality by refractile lesions that have
different refractive index than the media in which
they are contained.

65. Technique:
Slit beam: narrow to medium, slit height is
reduced, area of corneal pathology is
positioned directly over the slit beam light
reflected from the iris, either by moving the
instrument or by altering the patient’s gaze.

66. Direct retroillumination

67. Indirect retroillumination.

68. Retroillumination from the fundus:
• Terminology : Light entering the pupil is
reflected from RPE and choroid and emerges
from the pupil with orange red glow,
commonly called as red reflex.
• When examiner views the cornea against this
reflex he/she is able to detect lesions that
are to subtle for visualization by other
techniques.

69. • Principle: Same that of the Retroillumination
from iris.
• Dense scars : Obstructs the reflected and they
appear as dark silhouettes.
• Translucent/transparent objects: Corneal
guttae, DM Folds, Lattice corneal dystrophy,
epithelial oedema stands out as brightly
refractile contours.

70. • Technique: Slit lamp is aligned coaxial with
microscope. Then decentered to the edge of
the pupil.
• Slit width: Medium and curved at one edge to
fit in pupil.
• Slit height: Reduced to 1/3 .

74. Specular reflection
• Terminology: The smooth surfaces of cornea
reflect incident light like a plain mirror
following SNELL’S LAW.
• When angle of incidence is equal to angle of
reflection as measured from line drawn
perpendicular to the surface. THIS IS KNOWN
AS SPECULAR REFLECTION.

75. • Principle: Surface light reflex from the tear air
interface is brightest specular reflection emanating
from the cornea, but this does not permit examination
of individual epithelial cells, because the light is
reflected from tear film.
• Intensity of anterior reflection is great because the
difference in refractive index between air and tears is
large.
• Intensity of posterior reflection from endothelial
surface is much less because the difference in index of
refraction between aqueous humor and endothelium
is much less.

76. • Light Reflected from the endothelium is 0.22% of
total incident light.
• Because cornea is curved , only a small part of
the incident light beam is reflected in a specular
manner which forces the observer to narrow the
slit beam in to eliminate the surrounding glare.
• Mirror smooth posterior surface of endothelium
is broken by the intercellular spaces, which do
not reflect the light, thus appears dark
boundaries outlining a regular mosaic.

77. • The regular endothelial mosaic pattern can be
disrupted by various pathologic entities.
• 1) large and small cells may form a heterogeneous
population.
• 2)Irregularities in Descemet’s membrane e.g., cornea
guttata , ridges, folds may displace the endothelial
cells from the plane of reflected light so that they can
not be clearly visualised and localised black area is
viewed.
• 3)Pigment deposits/ keratic precipitates on the
posterior surface of the endothelium may reflect light
and may be seen as focal bright spots.

78. • Technique: It requires a more systematic, stepwise,
careful approach.
• Patient is asked to look straight ahead.
• Slit beam is projected on the central cornea from the
temporal side.
• The height of beam : 3 to 4 mm
• Width of beam: Moderately wide (0.5mm)
• Angle of slit beam and microscope should be same
from the perpendicular to the corneal surface.
• With this settings observer sees three lights:

79. • 1. Slit beam parallelepiped in the cornea.
• 2) Beam reflected from the iris nasal to the
parallelepiped.
• 3) The corneal light reflex( First Catoptric
image) temporal to parallelepiped.
• Examiner focuses the slit beam at the level of
the endothelium and slowly moves it
temporally towards the first catoptric image.

80. • As this being done entire corneal parallelepiped
changes in appearance from grey black to lighter
and brighter structure.
• When the corneal parallelepiped passes in front
of the catoptric reflection, the bright surface
reflex from the tear air interface dazzles the
examiner and faint mosaic pattern of the
endothelium becomes apparent, at this point
magnification is changed to high power.

84. Aqueous flare and cells
• Conical beam: is a small circular beam used to
examine the presence of cells and flare.
• Beam: Small circular pattern.
• Light Source:45-60’ Temporally and directed in to
the pupil.
• Biomicroscope: Directly in front of the eye.
• Magnification: High
• Focusing: Beam is focused between cornea and
anterior lens surface.

86. Filters
• Sodium fluorescein is applied gently to the bulbar conjunctiva.
• The patient should blink once or twice for the dye to be dispersed
over the eye.
• If the epithelium of the conjunctiva or the cornea is damaged, the
fluorescein stains the underlying tissue.
• The remaining dye fluoresces a yellow green colour when excited
by the blue light.
• Healthy epithelium does not stain.
• Uses:
• Contact lens fitting,
• Marginal tear film height measurement,
• Tear film break up time,
• Jone’s dye disappearance test

88. Red free filter
• The Red-free (green) filter to differentiate
vascular from pigmented lesions.
• Blood vessels and small haemorrhages will
take on a dark appearance with the use of the
red-free filter, whereas pigmented lesions will
remain dark.
• It makes the detail better by improving
contrast.

90. Clinical Slit Lamp Microscopy
• Examiner must integrate various types of illuminations in to flowing
examination of cornea that permits rapid and accurate observations of
corneal disease.
• An example for sequence of illuminations in which the corneal lesion is to
be seen:
• 1)Flash light/ diffuse illumination: To locate the pathology.
• 2)Sclerotic scatter: To see the pattern of abnormality.
• 3)Focal slit: To know the depth at which the lesion is located.
• 4)Proximal illumination : For internal details of the lesion.
• 5)Tangential illumination: For surface characteristics of the lesion.
• 6)Retroillumination from iris & fundus: For optical qualities of the lesion.

91. Clinical Drawings of Corneal
Pathology
Colour coding:
• Black:
• Corneal limbus,
• Scars ,
• Degenerations,
• Foreign Bodies,
• Suture,
• Contact lens.

92. • Blue: Designates oedema
1)Shading: Diffuse stromal oedema.
2)Small circles: Epithelial Oedema.
3)Wavy Lines: DM Folds.

93. • Brown: Indicates Melanin or Iron
Pigmentations
1)Pupil
2)Iris
3)Deposits of Melanocytes on Posterior
cornea.
4)Sundry Iron lines on the epithelium.

94. • Red
1) Blood vessels:
i) Wavy lines: Begin outside the limbus indicates
subepithelial vessels.
ii) Straight lines : Begin inside the limbus
indicates stromal vessels.
2) Rose bengal stain: RED DOTS indicates area
stained by rose bengal.
3)Solid red shades: Indicates haemorrhage.

95. • Yellow: indicates presence of white blood
cells.
• Hypopyon
• Stromal infiltrate
• Keratic precipitates

96. • Green: fluorescein staining of the cornea
• Green coloured dots: PEES
• Small Lines: Filaments
• Shaded Outlines: Epithelial Defect.

99. Accessory Devices:
• Gonioscopy.
• Pachymetry.
• Applanation tonometry.
• Slit lamp photography.
• Slit lamp as a delivery system for argon,
diode,and YAG laser.