Slit lamp evaluation

SLIT LAMP EVALUATION
Presenter: Dr. Manasi Nayak

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

• The slit-lamp is one of the most 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).
Three basic requirements for appreciation of depth:
1) The clinician possessing a third grade of binocular
vision called stereopsis.
2) The direction of the incoming light source (the light
beam can be moved so it comes in from one side or the
other).
3) The shape of the slit.

History
• Purkinje: One of the first individuals in 1823 to
apply microscopy to the living eye.
• He used one hand-held lamp to magnify another
hand-held lens to focus strong oblique illumination.

• Louis de Wecker : In 1863, he devised a
portable ophthalmomicroscope that combined
a small monocular microscope with an
attached condenser lens. It lacked stereoscopic
view.

• Albert and Greenough, in 1891, developed a binocular
microscope which provided a stereoscopic view.
• Siegfried Czapski, in 1897, modified the binocular
corneal microscope, which is still found in many
modern slit-lamps.
Czapski Czapski’s corneal microscope

• 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.

• Henker and Vogt, in 1916, developed the prototype of
the modern biomicroscopy by combining Gullstrand’s
slit-illumination system with the Czapski’s binocular
corneal microscope.
• Hans Goldmann, in 1933 improvised by placing all the
vertical and horizontal adjustments for lamp and slit-
beam on a single mechanical stage. This was marketed
in 1937 as the Haag-Streit model 360 slit-lamp.
Hans Goldmann

• Hans Littmann, in 1950, introduced the new
optical principle in the form of a rotatory
magnification changer based on the principle of
Galilean telescope. This slit-lamp is the
forerunner of the current Zeiss slit-lamp series.
• Modern slit-lamps have achieved a very high
degree of refinement.

Basic design of slit lamp
• The three main components of the modern
slit-lamp are:

Observation System (Microscope)
Should have following Characteristics :
• Optimum stereoscopic observation.
• Selectable magnification.
• Large field of view.
• Enough space in front of the microscope for
manipulations on the eye.

• The observation system is basically a
compound microscope composed of 2 optical
elements- an objective and an eye piece.
• It presents to the observer an enlarged image
of a near object.
• The slit-lamp microscope is designed to have a
long working distance (distance between
microscope’s objective and patient’s eye)

Composition
• Objective lens consists of 2 planoconvex lenses
with their convexities put together, giving a
composite power of +22 D.
• Eyepiece has a lens of +10 D. To provide a good
stereopsis, the tubes are converged at an angle of
10-15°.
• Prisms: To overcome the problem of inverted
image formed by compound microscope, a pair of
prisms is used between the objective and the
eye-piece to reinvert the image.

Magnification Systems
• Range of magnification- 6× to 40×
• Modern slit lamps use one of the three
magnification systems:
1. Czapskiscope with rotating objectives
2. The Littmann-Galilean telescope principle
3. Zoom system

Czapskiscope with rotating objectives
• One of the oldest and still most frequently
used techniques.
• Different objectives placed on a turret type of
arrangement allows them to be fairly rapidly
changed during the examination.
• The Haag-Streit model, the Bausch and Lomb
and the Thorpe are some slit-lamps using this
system.

The Littmann-Galilean telescope
principle
• In 1950, Littmann developed the Galilean
magnifiation changer, a completely separate
optical system that sits between the objective
and eyepiece lenses and doesn’t require
either of them to change.
• Provides a large range of magnifications,
typically 5 via turret arrangement.
• Utilizes Galilean telescopes to alter the
magnification.

• Galilean telescopes have 2 optical
components- a positive lens and a negative
lens.
• It fits within the standard slit-lamp microscope
along with a relay lens and the prism erector.
• The Zeiss, the Rodenstock and the American
optical slit-lamps use this system.

Zoom System
• Allows a continuously variable degree of
magnification.
• Nikon photo slit-lamp and Zeiss-75 SL use this
system.
• Nikon slit-lamp contains the zoom system
within the objective of the microscope.
• Range of magnification- 7× to 35×

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

Magnification can also be changed
by changing the eyepiece power

Illumination System
• The Gullstrand’s illumination system is
designed to provide a bright, evenly
illuminated, finely focused adjustable slit of
light at the eye.
• It has the following components:
1. Light source
2. Condenser lens system
3. Slit and other diaphragms
4. Filters
5. Projection lens
6. Reflecting mirror or prism

Typical slit-lamp illumination system

Components
• Light source: Nernst lamp  Nitra lamp 
Arc lamp  Mercury vapour lamp  Halogen
lamps. Provides an illumination of 2×105
to
4×105
lux.
• Condenser lens system: A couple of
planoconvex lenses with their convex surfaces
in apposition.

• Slit and other diaphragms: Height and width
of the slit can be varied using 2 knobs.
• There are stenopaeic slits of 2.0 and 0.5 mm
to provide conical beam of light.

• Filters: Different filters can be inserted into
the illumination beam. Cobalt blue and red-
free (green) filters are provided in most
models.

Cobalt blue filter
• Cobalt blue filter produces light of wavelength
450 to 500nm.
• This filter is used to look for pathology in the
cornea once it has been stained with fluorescein.
• Dye pools in the area where the corneal
epithelium is broken or absent.
• The dye absorbs blue light and emits green.
• Other uses are for applanation tonometry, tear
break up time measurement, Seidel’s test, Jones
dye test.

Fluorescein stain highlighting dendritiform
lesions in herpetic keratitis

Red-free (green) filter
• Obscures any thing that is red, hence the
name red free light, thus blood vessels or
haemorrhages appear black.
• Red-free light is absorbed by the RPE, creating
increased contrast.
• 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.

• Increased vessel detail: red-free light gives a better contrast
between retinal vessels and the underlying background. The
retinal vessels, and other blood on the retina, will look black,
so that subtle changes (e.g., small hemes, ill-defined
exudates, etc.) will stand out more.
• Assessing depth of pigmented lesions: retinal lesions will look
black and choroidal lesions will either disappear or become
dimmer/gray.
• Detecting early losses of the NFL: handy for suspected
glaucoma or optic nerve disease because the red-free light
bounces off the NFL, making it easier to see; loss of the usual
“stripey” look to the NFL with the red-free filter could indicate
nerve fiber loss.
• Good for light sensitive patients: decreases the intensity of
the light while still enhancing retinal details.

Fleischer ring can also be
viewed satisfactorily with the
red free filter.

Yellow filter
• In RGP lens fitting the amount of fluorescein
indicates a good or bad fit. RGP fit is better seen
using an orange/yellow filter (Kodak Wratten
#12), which significantly enhances the contrast
of fluorescein staining observed with the cobalt
blue light.

Neutral density filter: Decreases maximum
brightness for photosensitive patients
Diffuser: 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.

Projection lens: Forms an image of
the slit at the eye. Small diameter
of this lens has 2 advantages:
1. Keeps aberrations of lens
down better quality image
2. Increases depth of focus of
slit better optical section of
the eye

• Reflecting mirror or prism: Illumination
system has to be able to pass relatively easily
from one side of the microscope to the other.
• For this, projection system is arranged along
vertical axis with either a mirror or prism
reflecting the light along horizontal axis.
• While examining fundus, illumination axis can
be made to almost coincide with viewing axis
without obstructing field of view.

Optics of the Illumination system
• Koeller illumination system is used in slit lamps.
• Optically, it is identical to a 35 mm slide
projection except a variable aperture slit takes
the place of a slit and projection lens has a
shorter focal length.
• The filament of the light source is imaged by the
condenser lenses at or close to the projection
lens which forms the image of the slit in the
patient’s eye.

• 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.
The second design: the Zeiss type illumination
system, does not allow decoupling in
the vertical meridian.

Mechanical Support System
It is mainly concerned with:
• Positioning of the patient.
• Adjustment for observer and patient.
• Adjustment of illumination and observation
systems.

• Joystick arrangement: Movement of the
microscope and illumination system towards
or away from the eye and from side to side.
• Up and down movement arrangement: Some
sort of screw device moves the whole
illumination and viewing system up and down
relative to the chin rest.

• Patient support arrangement: Vertically
movable chin rest and provision to adjust
height of the table- to accommodate persons
of all sizes.

• Fixation target: A movable fixation target
facilitates examination under some conditions.

Mechanical Coupling
• Coupling of microscope and the illumination
system along a common axis of rotation that
coincides their focal planes.
• Ensures that light falls on the point where
microscope is focused.
• Allows either microscope or illumination
system to be rotated around this axis without
changing the focus.

• This coupling is advantageous for routine
examination of anterior segment of the eye.
• It can be a disadvantage when gonioscope or
three-mirror fundus lens are used, since the
slit and microscope optics frequently don’t
reach a common focal point leading to sub-
optimal images or observer has to refocus the
eyepieces.

Technique of biomicroscopy
• 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).

• 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).

• Patient adjustment: Patient should be
comfortably positioned in front of the slit-
lamp with his or her chin resting on the chin
rest and forehead opposed to 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.

• Instrument adjustment: Height of the slit-
lamp table should be adjusted according to
patient’s height.
• Microscope and illumination system should be
aligned with patient’s eye to be examined.
• Fixation target should be placed at the
required position.

Beginning slit-lamp examination
• Examination should be done in a semi-dark room so
that the examiner’s eyes are partially dark adapted to
ensure sensitivity to low intensities of light.
• Diffuse illumination should be used for as short a time
as possible.
• There should be a minimum exposure of retina to light.
• Medications like ointments and anaesthetic eye drops
produce corneal surface disturbances which can be
mistaken for pathology.
• Low magnification should be used first to locate the
pathology, then higher magnification should be used to
examine it.

• Focus the slit-beam on the eye by moving the
joystick either towards or away from the patient.
• 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.

METHODS OF ILLUMINATION
• Berliner – 7 basic methods of illumination
1) Diffuse illumination
2) Direct focal illumination
3) Indirect illumination
4) Retroillumination
5) Specular reflection
6) Sclerotic scatter
7) Oscillating illumination of Koeppe

DIFFUSE ILLUMINATION
• Allows observer to obtain a direct and
tangential view of anterior segment of eye.
• Direct diffuse illumination with low
magnification is done first, then by higher
magnification for viewing areas of interest.
• General features like colour, size and relative
position of structures seen.
• Tangential illumination with a large angle
increases contrast and highlights texture of
ocular tissues.

DIFFUSE ILLUMINATION
• Microscope- directly in front of patient’s eye
at 0°; achromatic light on anterior of cornea.
• Angle between microscope and illumination
system- 30-45°.
• Slit width- widest.
• Filter- diffusing filter.
• Magnification- low to medium.
• Illumination- medium to high.

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

Uses
• General view of
anterior eye
and palpebral
conjunctiva
esp., for gross
inspection,
corneal scars,
lid irregularities
and tear debris.

• Cobalt blue
filters and
fluorescein
sodium-
corneal and
conjunctival
epithelium
and tear break
up time.

• Rose Bengal
staining with
achromatic
light- pink
staining of
damaged
epithelial cells.

DIRECT FOCAL ILLUMINATION
• Slit beam regulated until it coincides with
exact focus of microscope.
• Light directed as a narrow slit at an oblique
angle- 30-45°.
• Heterogenous tissues like cornea and lens
disperse light and become visible as bright
objects against a dark background.

Optics of direct focal illumination

• Carried out using 3 slit beam effects
i. Optical section
ii. Parallelopiped
iii. Conical beam

Optical section
• Produced by a very narrow slit beam focused
obliquely.
• Angle between illuminating and viewing path
kept small to minimize dazzling.
• Slit is narrow- 0.1-0.25 mm wide and 7-9 mm
high.
• Magnification- 7-10×.

• Height of coaxial beam adjusted to measure
horizontal and vertical size of lesion.
• Resembles knife like histological section of
tissue focussed.
• Whole tissue examined by moving slit beam
and simultaneous focus of microscope across
the surface.

Corneal optical section
Consists of a segment of an arc with following
concentric zones:
• Tear layer- bright anterior most zone.
• Epithelium- dark line immediately behind tear
layer.
• Bowman’s membrane- bright line.
• Stroma- wider granular and greyer zone.
• Descemet’s membrane and endothelial layers-
posterior most bright zone.

Uses of corneal optical section
• Changes in corneal curvature.
• Changes in corneal thickness.
• Depth of corneal pathologies.
• Anterior chamber angle grading by van Herick
method at nasal and temporal periphery.

Corneal scar with wide beam
illumination
Optical section through scar
indicating scar is with in
superficial layer of cornea

Van Herick grading of anterior chamber depth
van Herick grade Limbal anterior chamber
depth: corneal section
thickness (expressed as a
fraction)
Modified van Herick grade
with the limbal anterior
chamber depth expressed
as a percentage of corneal
section thickness
Grade 0 0 (closed) 0%
Grade 1 <1/4 5%
15%
Grade 2 1/4 25%
Grade 3 1/4 to 1/2 40%
75%
Grade 4 1 or greater than 1 ≥100%

Optical section of lens
Shows stratification of lens into following layers
from front to backwards:
• Anterior capsule (Ca)
• Subcapsular clear zone (first cortical clear zone
C1α)
• Bright narrow scattering zone of discontinuity
(first zone of disjunction C1β)
• Second cortical clear zone (C2)

• Light scattering zone of deep cortex (C3)
• Clear zone of deep cortex (C4)
• Nucleus (N)- prenatal part of lens;
stratification with central clear interval-
embryonic nucleus
Microscope needs to be shifted forward to focus
more posterior layer.
Location and extent of lenticular opacities can
be easily made.

Optical section of lens
Anterior capsule
1st cortical clear zone
1st zone of disjunction
2nd cortical clear zone
Light scattering zone of deep
cortex
Clear zone of deep cortex
Nucleus

• Optical section of anterior one-third of
vitreous can also be studied with slit lamp
beam.

Parallelopiped of cornea
• 2-3 mm wide focused slit used.
• Light source 45-60° temporally, directed onto
pupil.
• Magnification- 7-10×.
• Room darkened.

Uses
• Pathologies of epithelium and stroma better
studied.
• Corneal scars or infiltrates appear brighter
than surroundings (more density).
• Water clefts have decreased optical density, so
appear black in optical block.

• Zone between out of focus cornea and lens-
optically empty, appears totally black.
• Flare- makes optically empty zone appear
milky or grey.
• Flare graded based on degree of interference
in visualization of iris.

• WBCs reflect light, seen as white dots floating
in anterior chamber.
• Number of cells seen during a minute period
is counted and graded accordingly.
• Grading done using parallelopiped 2 mm wide
× 4 mm high.

Conical beam
• Used to examine presence of aqueous flare.
• Beam- small circular pattern.
• Light source- 45-60° temporally, directed onto
pupil.
• Biomicroscope- directly in front of eye.
• Magnification- high (16-20×).

• Focusing- beam focused between cornea and
anterior lens surface.
• Dark zone between cornea and lens observed.
• Normally optically empty and appears black.
• Flare appears grey or milky.
• Cells seen as white dots.
• Cells located by gently oscillating illuminator.

INDIRECT ILLUMINATION
• Slit beam focused on a position just beside the
area to be examined.
• Angle between slit lamp and microscope- 30-
45°.
• Beam width- moderate (2-4 mm).
• Illumination- low, medium or high.
• Slit lamp can be offset.

Optics of indirect illumination

Uses
To observe
• Corneal infiltrates
• Corneal microcysts
• Corneal vacuoles
• Epithelial cells

RETROILLUMINATION
• Light reflected off iris or fundus while
microscope focused on cornea.
• Provide information regarding form, refractive
index and consistency of pathology.
• Graves divided retroillumination as direct and
indirect, depending on angle between
observer and light.

Direct retroillumination
• Slit width- 1-2 mm wide and 4-5 mm high
• Biomicroscope and light source placed in
direct alignment with each other.
• Observer in direct pathway of light reflected
from structures.
• Pathology seen against an illuminated
background.

Optics of direct retroillumination

Indirect retroillumination
• Observer at right angle to observed structure,
not in line with light.
• Pathology seen against dark nonilluminated
background.

Optics of indirect retroillumination

Based on optical properties, Graves divided
pathologies as follows:
• Obstructive- opaque to light, seen as dark
against bright background. e.g., pigment or
blood-filled vessel.

• Respersive- scatter light but don’t obstruct
light completely, seen brightly against dark
background. e.g., epithelial oedema,
precipitates.
Infiltrates are relucent in direct focal
illumination but respersive in direct
retroillumination.

• Refractile- distort view of junction of
illuminated and dark areas because their
refractive index is different from surroundings.
e.g., vacuole

• Vacuole seen as illuminated area bordered by
dark line in direct retroillumination, but in
indirect retroillumination seen as black area
with bright surface towards illuminated area
(unreversed illumination)
• Solid or opaque precipitate seen as dark area
in direct retroillumination, but in indirect
retroillumination the side away from
illuminated area is bright (reversed
illumination).

Retroillumination from fundus
• Used to observe media clarities and opacities.
• Pupil is dilated, slit beam and microscope
made coaxial.
• Light directed to strike fundus and create a
glow behind opacity in media.
• Media opacity creates a shadow in glow.
• Microscope focused on pathology directly and
10-16× magnification used.

Optics of retroillumination from fundus

• Cornea, lens and vitreous pathologies
examined by this technique.
• Retroillumination of crystalline lens required
to classify and grade both cortical and
posterior subcapsular cataracts using LOCS III
(Lens Opacity Classifying System III).

SPECULAR REFLECTION
• Reflection of light occurs when a beam of light
is incident on an optical surface called zone of
discontinuity.
• Found in cornea and lens.
• Observer placed in pathway of reflected light-
a dazzling reflex- specular reflection.
• Surface from which reflection is obtained-
zone of specular reflection.
• Surface pathologies- scatter light irregularly-
dark areas in reflex.

• Patient asked to look 30° temporally.
• Light beam directed from opposite side.
• Optical block focused under high
magnification, 3-4 mm from limbus.
• Towards the side of light source, a shining
reflex seen on cornea.
• When light source rotated temporally, optical
block approaches the reflex.

• When angle between microscope and slit
beam is 60° (angle of incidence= angle of
reflection), dazzling reflex from tear meniscus
shows its irregularities.
• At the same time, a deeper less luminous glow
is seen which on focusing shows endothelial
mosaic.
• Parallelopiped beam with high illumination
and high magnification used.

• Specular reflection from anterior and
posterior capsule of lens can be obtained.
• Using an eyepiece reticule, endothelial cells
can be measured and counted.
• To study tear film details.
Reflection from front surface
Endothelium

SCLEROTIC SCATTER
• Used to outline even the faintest corneal
pathology.
• Light beam focused on limbus.
• Because of total internal reflection, rays of
light pass through substance of cornea and
illuminate opposite side of limbus.
• Pathology like corneal opacity becomes visible
as it scatters rays of light.
• Magnification- 6-10×, microscope directed
straight ahead.

OSCILLATING ILLUMINATION OF
KOEPPE
• Slit beam given oscillatory movement.
• To see minute objects or filaments esp., in
aqueous which would escape detection.

ACCESSORY DEVICES
Specialized examinations with help of slit lamp
biomicroscope using accessory devices:
• Gonioscopy
• Fundus examination with focal illumination
• Pachymetry
• Applanation tonometry
• Ophthalmodynamometry
• Slit-lamp photography

• Slit-lamp videography
• Slit-lamp as delivery system for argon, diode
and YAG laser
• Laser interferometry
• Potential acuity meter test

Slit lamp evaluation

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