Md. Didarul alam2nd year

B. Optom,ICO,CU

Slit lamp Biomicroscopy

optometrist

Introduction

• Biomicroscope derives its name from the fact that it enables the clinician 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.

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.

Large GullstrandOphthalmomicroscope (1911)

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.

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

Fig:2

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

Instrumentation

• Operational components of slit lamp biomicroscope essentially consist of:– Illumination system– Observation system– Mechanical system

• 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.

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.

The illumination and observation systems coupled around a common centre of rotation to ensure that the microscope is always focused at the same point as where the slit beam is focused.

Observation system(microscope) Observation system is 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 facing towards the patientproviding 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 + 14D towards the examiner.

• 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/Physical support

• A joystick control is employed to enable instrument to be moved left-right/forward-backward (= focus)/ and up-down.

• A chin rest, head rest and fixation target is also required. Some slit lamps have a tilting mechanism to enable the lamp to be directed from different angles.

– Used in conjunction with fluorescein stain– absorbs blue light and emits green with

fluorescein stain. Uses:

• Ocular staining• RGP lenses fitting• Tear layer

Cobalt blue filterFilters used in slit lamp biomicroscopy

Continue…….. Obscure any thing that is red hence the red

free light , thus blood vessels or haemorrhages appears black.

• is used to see the vascular pattern of choroid and see any abnormalities in the disc of fundus.

• Fleischer ring can also be viewed satisfactorily with the red FREE filter

• Yellow filter is used for general view of anterior

segment.

RED FREE FILTER

YELLOW FILTER

Illumination techniques

– Diffuse illumination– Direct illumination

• Parallilepiped• Optic section• Conical(pinpoint)• Tangential• Specular reflection

– Indirect illumination• Retro-illumination• Sclerotic scatter• Transillumination

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.

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

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.

Dirrect illumination

Slit beam and microscope are focused on the same area

Vary angle of illuminationLow to high

magnificationVary width and height of

light source

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DIRECT ILLUMINATIONDIRECT ILLUMINATION

• Optic Section

- narrow, focused light

• Parallelepiped

- wider, focused light

• Conical Beam

- small, circular light

• Optic Section

- narrow, focused light

• Parallelepiped

- wider, focused light

• Conical Beam

- small, circular light

Optic section

• Optic section is a very thin beam of light and optically cuts a very thin slice of the cornea.

• Angle between illuminating and viewing path is 45 degree.

• Used to localize:– Nerve fibers – Blood vessels– Infiltrates– Cataracts– AC depth.

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.

• 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.

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PARALLELEPIPEDPARALLELEPIPED

A A'

B B'

– 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.

UsesMost useful when examining the transparency of anterior

chamber for evidence of floating cells and flare seen in anterior uveitis.

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CONICAL BEAMCONICAL BEAM

MicroscopeMicroscopeConical beamConical beam

CorneaCornea

Iris

Conical BeamConical Beam

Beam cross-section

Indirect illumination

• Lights enter the eye through a narrow to medium slit (2 to 4 mm) to one side of the area to be examined

• Illumination narrow to medium slit width decentred slit• Magnification• approx. M= 12x (depending on object size)

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INDIRECT ILLUMINATIONINDIRECT ILLUMINATION

MicroscopeMicroscope

Beam of lightBeam of light

CorneaCornea

Iris

Observe

valuable for observing• Epethelial vessicles• Epithelial erisons• Irish pathology• Irish spincter

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RETRO-ILLUMINATIONRETRO-ILLUMINATION

• Vary angle of illumination

• Moderately wide beam

• Slit beam is offset

• Medium to high magnification

• Reflected light from iris or fundus

• Vary angle of illumination

• Moderately wide beam

• Slit beam is offset

• Medium to high magnification

• Reflected light from iris or fundus

Schematic ofretroillumination from the retina.

Example of retroillumination from the retina.

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RETRO-ILLUMINATIONRETRO-ILLUMINATION

Valuable for observing:• vascularisation• epithelial oedema• microcysts• vacuoles• dystrophies• crystalline lens opacities• contact lens deposits

Valuable for observing:• vascularisation• epithelial oedema• microcysts• vacuoles• dystrophies• crystalline lens opacities• contact lens deposits

Retroillumination

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.

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SPECULAR REFLECTIONSPECULAR REFLECTION

MicroscopeMicroscopeBeamof lightBeamof light

CorneaCornea

Iris

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SPECULAR REFLECTIONSPECULAR REFLECTION

Valuable for observing:

• endothelial cell layer

• tear film debris

• tear film lipid layer thickness

Valuable for observing:

• endothelial cell layer

• tear film debris

• tear film lipid layer thicknessReflection from front surface endothelium

Sclerotic scatter

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

• total internal reflection occurs here• 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– Epithelial defects– Corneal endothelial cell counts– Corneal abrasions– Corneal nebulae and maculae.

Schematic ofsclerotic scatter. Example of sclerotic

scatter.

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.

• Observe:– Anterior and posterior cornea– Iris is best viewed without dilation by this

method.– Anterior lens (especially useful for viewing

pseudoexfolation).

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TANGENTIAL ILLUMINATIONTANGENTIAL ILLUMINATION

MicroscopeMicroscope

Beam of lightBeam of lightCorneaCornea

Iris

Order of Examination

• Tears• Lid margins/Lashes• Conjunctiva• Cornea• Anterior chamber• Iris • Lens • Anterior vitreous

Clinical Use

Diagnostic – Anterior segment Evaluation– Goldmann Applanation Tonometry– TBUT test– Staining (Flurescein, Rose Bengal etc.)– Visiometry– Gonioscopy– FFA and Clinical Photography– Tear evaluation– Pachymetry

• Therapeutic– Epilation– Foreign Body Removal– Contact Lens (fitting and post-wear

evaluation)– Corneal epithelial debridement (herpetic

keratitis)– Insertion of punctal plugs

References

• Clinical ophthalmology- jack j kanski• Comrephensive ophthalmology- A K Khurana• Clinical procedurs in optometry(CPO)• Optics & refraction – A K khurana• internet

THANK YOU