SLIT LAMP BIO-MICROSCOPY

PRESENTED BY :- JINAL DHARA

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.

• 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.

IMPORTANT HISTORICAL LANDMARKSDe 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.

Large GullstrandOphthalmomicroscope (1911)

TYPESThere 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.

Zeiss slit lamp biomicroscopeHaag streit slit lamp biomicroscope

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

INSTRUMENTATIONOperational components of slit

lamp biomicroscope essentially consist of:Illumination systemObservation systemMechanical system

Illumination system

It consist of:

A bright ,focal source of light with a slit mechanismThe beam of light can be changed in intensity,height,width,direction or angle and color during the examination with the flick of lever.

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.

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.

Reflecting mirrors and prismsFilters

Yellow barrier filter Red free filterNeutral density filter Cobalt blue filterdiffuser

OBSERVATION SYSTEM(MICROSCOPE)

Observation system is essentially a compound microscope composed of two optical elements1.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 togetherproviding a composite power of +22D.

Microscope is binocular i.e. it has two eyepieces giving binocular observer a sterescopic view of eye.

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

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

provision to adjust height of table.

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 segment of eye.

Magnification control :Including two or pair of readily

changeable objective lenses and two sets of eyepieces.

An on and off switch and illumination

control .

Topcon slit lamp model SL-3E

Light beam is controlled by knobs

Joy stick arrangement

Chin rest

Reflecting mirror

biomicroscope

Illumination control

Magnificationmay be changed byflipping a lever...

Changing filters. biomicroscope

Patient positioning

Alignment mark

Microscope and light source rotate indepedently

FILTERS USED IN SLIT LAMP BIOMICROSCOPY

Cobalt blue filterUsed in conjunction with fluorescein staindye pods in area where the corneal

epitheliumis broken or absent.

The dye absorbs blue light and emits green. Uses:

Ocular stainingRGP lenses fittingTear layer

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.

ILLUMINATION TECHNIQUES Includes

Diffuse illumination Direct illumination

Parallelepiped Optic section Conical(pinpoint) Tangential Specular reflection

Indirect illumination Retro-illumination Sclerotic scatter Transillumination Proximal illumination

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.

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.

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

Direct illumination

Application: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.

Direct illumination is divided into three types

1.parallelopiped 2.conical beam effect 3. optical section

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.

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.

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.

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.

Most useful when examining the transparency of anterior chamber for evidence of floating cells and flare seen

in anterior uveitis.

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.

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 .

Used to localize:Nerve fibers Blood vesselsInfiltratesCataractsAC depth.

TANGENTIAL ILLUMINATION(OSCILATING 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.

Observe:Anterior and posterior corneaIris is best viewed without

dilation by this method.Anterior lens (especially useful

for viewing pseudoexfolation).

Example of tangential illumination (iris).

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)

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.

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

endotheliumLens surfaces Corneal epithelium

Schematic of specular reflection.

Reflection from front surface endothelium

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.

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

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 .

Schematic ofdirect retroillumination fromthe iris.

direct retroillumination from the iris.

Indirect retro-illumination from iris:Performed as with direct retro-

illumination 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.

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.

Used to observe:Central corneal epithelial edemaCorneal abrasionsCorneal nebulae and maculae.

Schematic ofsclerotic scatter. Example of

sclerotic scatter.

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 the abnormality.

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

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..

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)

BASIC SLIT LAMP EXAMINATION

Patient positioning:Head support unitAdjust height of table or chairAdjust height of chin rest such

that patients lateral canthus is aligned with the mark.

Adjust ocular eyepieces.

Power upFixationMagnification : begin with 6x -10x magnification

FocusingSpecial proceduresProtocol and documentation

USES OF SLIT LAMP BIOMICROSCOPY

Diagnostic:OCT- Optical coherence of tomographyFFA-Anterior segment and posterior

segment diseasesDry eye

Procedures:ApplanationTear evaluationPachymetryGonioscopyContact lens fittingTherapeutic:

LaserFB removalepilation

ANTERIOR AND POSTERIOR SEGMENT DISEASE EVALUATION

Lids and lashesConjunctiva and cornea Instillation of fluorescein and BUT

measurementEversion of the lidsAnterior chamber and angle

measurement IrisCrystalline lensAnterior vitreous

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