Slit lamp biomicroscope



Slit-lamp biomicroscope

Transcript of Slit lamp biomicroscope

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SESSION – JULY, 2013 25-09-2014

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THE SLIT-LAMP BIOMICROSCOPE is a high-power binocular microscope with a slit-shaped illumination source, specially designed for viewing the different optically transparent or translucent tissues of the eye.

It enhances the examination by :

Excellent image quality

Binocular stereoscopic view

Flexible illumination

Flexible magnification

Providing room for specialized attachments and lenses for detailed examination and diagnostic tests

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The science of examination with a slit lamp is

called Biomicroscopy as it allows in vivo study of living tissues at high magnification.


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• 1911, the first concept of slit-lamp was introduced by ALLVAR GULLSTRAND, it was named as “Large reflection-free ophthalmoscope” manufactured by Zeiss.

Prof. Allvar Gullstrand Large Gullstrand Opthalmoscope (1911)

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• 1919, VOGT introduced KOEHLER illumination system to Gullstrand slit-lamp.

• 1930, LETZ introduced telescopic loupe built on the principle of Galilean Telescope which helps in increase working distance.

Haag-Streit-1920 Bausch & Lomb slit lamp (1926)


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• 1933, GOLDANN developed three control element for cross-slide stage and also common swivel axis for microscope and illumination system in HAAG-STREIT Slit-lamp.

• 1938, Joystick was added to Haag-streit.

Haag-Streit-1933 Haag-Streit-1936


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• 1950, LITTMANN with ZIESS combined joystick control from Goldmann, illumination path from Comberg prism instrument and also added stereo telescope system with magnification changer.


Zeiss slit lamp (Littmann) (1950) Haag-Streit-1959

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Fig. : Modern slit-lamp


• Onward modern slit-lamp system began to come into light.

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• On the basis of illumination system it is of 2 types :

1. Zeiss type

In the Zeiss type the illumination comes from below

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2. Haag-streit type

In the Haag Streit type the illumination comes from above


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• On the basis of compound microscope system it is also 2 types :

1. The Grenough type

Flip lever to change magnification


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2. The Galilean changer type

Knob to change magnification (3 or 5 step)


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Also different types of HAND-HELD slit-lamp devices available for –

• Handicap

• Infant

• Bedbound patients


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Illumination system Principle :

Kohler illumination principle is used in both Zeiss & Haag-streit type illumination system.

The light filament (F) is imaged on to the objective lens (O) but the mechanical slit (MS) is imaged on to the patient’s eye (S)

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Microscope system Principle :

The eyepiece (Ocular) uses Astronomical telescope system.

Here two convex lenses used one in front of other separated by the distance of their focal length.

Fig. : Slit-lamp biomicroscope optical principles

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A Galilean telescope system is used for even higher and changeable magnification.

Here a convex and a concave lens is used in line separated by the distance of their focal length.


Fig. : Slit-lamp biomicroscope optical principles

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Both telescope systems produce inverse image of an object so an inverting prism named Porro-Abbe prism is used to produce right way erect image.

Here two triangular prisms use the total internal reflection principle of optics.


Porro-Abbe Prism

Fig. : Slit-lamp biomicroscope optical principles

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The telescope system provide considerable distance between the microscope and the patient’s eye, so that certain maneuver like foreign body removal from the cornea or using extra lenses for fundus examination can be done.


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Parfocality : The point at which the microscope is focused corresponds to the point on which the light is focused, this coupling effect is called parfocality.

This is achieved by the microscope and the illumination system, having a common focal plane and their common axis of rotation also lies in that focal plane.


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Basic Design :

1. Mechanical system

2. Illumination system

3. Biomicroscope /Observation system

Associated instruments : • Applanation Tonometer

• Gonioscopic Lens

• Fundoscopy Lens

• Micrometer Eyepieces

• Image archiving device

• Laser delivery system

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It concern with :

• Positioning & adjustment of patient and observer

• Maneuvering the illumination and microscope system together with joystick

• Providing base to other parts

Mechanical system : Basic 3 parts :

1. Motorized table (Base)

2. Patient positioning frame

3. Joystick

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Parts of mechanical system :


Fixation target

Chin rest adjustment



Power switch

Table height adjustment

Forehead band

Canthus alignment

Chin rest

Hand grip for patient

Lock for slit lamp base

Low friction plate

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Provides a bright, evenly illuminated, finely focused, adjustable slit of light at the eye.

Contains the following components: • Light source • Condenser lens system • Slit and other diaphragms • Filters • Projection lens • Reflecting mirror or prisms

Illumination system :

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Parts of illumination system :


Scale for slit height

Slit height control

Inclined mirror

Latch to tilt

light column

Light source

Filter control

Centering screw

Slit width control

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• Essentially these are compound microscopes composed of optical elements providing enlarged right way stereoscopic image to observer.

• Provides larger working distance in front of microscope for manipulation on patient’s eye.

• Magnification changer for detail view.

Observation system :

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Parts of observation system :



Marked ring for

Adjustment of examiner’s

refractive error

Prism housing

Knob to change


Objective lens

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Associated instruments :

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Prerequisites :

• Switch on power & unlock base screw

• Cleaning the forehead band

• Changing paper strip from chinrest

• Comfortable sitting of pt. and the examiner

• Counseling the patient

• Proper positioning of the pt.

• Target fixation

• Adjust eyepieces to correct for examiner’s refractive error and interpupillary distance

• Children may need to stand, or they can sit on parent’s lap or kneel on a stable chair

Fig. Correct positioning at the slit lamp.

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Chronology for slit-lamp examination :

Eyelids Eyelid

margins Tear film

Conjunctiva Cornea Aqueous humor

Iris Lens Vitreous


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Illumination techniques :

Slit Width control knob:

Narrow to fully open slit illumination achieved by rotating this knob

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Illumination techniques :

Slit height control knob :

Short to long slit illumination achieved by rotating this knob


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Illumination techniques :

Slit angle rotation :


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Illumination techniques :

Tilting light column : Illumination column can be tilted 5-20°, with vertical axis which gives extra plane and minimize reflection during posterior segment examination with condensing lens.


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Illumination methods :

Direct illumination • Direct diffused illumination

• Direct focal illumination

i. Parallelepiped

ii. Optical section

iii. Conical beam

• Specular reflection

• Tangential illumination

Indirect illumination • Indirect proximal illumination

• Retro-illumination

• Sclerotic scatter

Oscillatory illumination

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Direct diffused illumination :

• illumination of the eye with a broad, unfocused light beam

• directed obliquely between 30-450

• magnification 6x to 10x

Application :

• General gross overview of eyelids, lashes, conjunctiva, sclera, pattern of redness, iris, pupil, gross pathology, ant capsule of lens


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Direct diffused illumination :


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Direct focal illumination :

• Illumination and observation are focused in the same plane

• slit width narrow to broad

• Illumination angle 45° to 60°

• Magnification 10x-40x

Application :

• Cornea in detail

• Anterior chamber

• Crystalline lens

• Anterior part of vitreous

• Grading cell and flare in anterior chamber


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Direct focal illumination :


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Direct focal illumination :

i. Parallelepiped

• Slit width 2-4 mm obliquely focusing on the cornea so that a quadrilateral block of light illuminate the cornea

Application :

• To examine corneal surface, stroma

• To ascertain depth (FB, abration)


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Direct focal illumination :

ii. Optical section

• Slit width 1mm or less

• Illumination angle 45-60° or more

• High illumination & magnification


• Corneal depth, layers, scars, vessels

• Lens opacity


1. Tear film 2. Epithelium 3. Ant. Stroma 4. Post. Stroma 5. Descemet’s mem. & Endothelium

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Direct focal illumination :

iii. Conical beam

• Assessment of particles floating in the A/C

• Narrow, short & bright slit of light

• 45°-60° light source directed to pupil

• Magnification 16x-25x

Application :

• Inflammatory cells, flare, pigmented cells, metabolic wastes

Principle : Tyndall phenomenon


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Specular reflection : • Angle of incidence = angle of


• Observation and illumination system have same angle with perpendicular axis to each other

• Slit width < 4mm

• The light reflected from the anterior or posterior corneal surface

• Best view with one eye

Application : • assessment of surfaces

Corneal epithelium

Corneal endothelium

Lens surface

• assessment of tear film


Corneal endothelium

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Tangential illumination :

• A narrow light beam is projected almost parallel along the structure to be observed

• Elevated structures are visible by shadowing

• Illumination angle 90°

• Magnification 10-25x

Application :

• elevated abnormities or changes in the iris

• tumors, cysts


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Indirect illumination : • The beam is focused in an area

adjacent to ocular tissue to be observed

• Decentered beam

• Illumination 2 to 4mm slit

• Magnification: Low to medium (depending upon object size)

Application: • infiltrates

• corneal scars

• deposits

• epithelial and stromal defects


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Indirect illumination :


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Retro-illumination :

• Light reflected on iris or fundus

• Microscope focused on cornea

• Two types: direct and indirect

Application :

For better visualization of

• Epithelial cysts

• Keratic precipitates

• Small blood vessels

• Small scar


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Direct retro-illumination :

• Observed feature is viewed in direct pathway of reflected light

• with this illumination findings are made visible with high contrast

• medium slit width 2 to 4mm

• Illumination angle 45-60°

Application :

• Infiltrations, small scars, corneal vessels, etc.


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Indirect retro-illumination :

• Observer at right angle to the observed structures

• Illumination angle greatly reduced or increased

• Feature on the cornea is viewed against a dark background

• medium slit width 2 to 4mm

Application :

• Infiltrations, small scars, corneal vessels, micro cysts, vacuoles


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Retro-illumination :


Indirectly illuminated


Direct retro-illumination

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• This technique is used to observe media clarities and opacities.

• The pupil is dilated

• the slit beam and microscope are made co-axial and light strikes the fundus and creates a glow behind the opacity in the media

• The media opacity creates a shadow in the glow


• abnormities in the anterior vitreous, lens, anterior chamber, cornea


Retro-Illumination from the Fundus :

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Sclerotic scatter : • Light incident on the limbus

with 2-4mm slit at an angle of 45° - 60°

• Decentered slit

• The microscope focused centrally

• Total internal reflection of the incoming light at inner corneal boundaries (endothelium and epithelium)


• scars, foreign bodies, corneal defects

• irregularities in the cornea


Fig. : Corneal scar

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Iris-transillumination :

• Transillumination of the iris by indirect light reflected from the fundus

• Mid dilated pupil (3 to 4mm)

• Illumination and observation at coaxial position


• Visualization of defects of the pigment layer of the iris


Fig. : Transillumination in Albinism

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Oscillatory illumination :

• Moves the beam (usually an optical section) from nasal to temporal limbus

• Viewed alternately by direct and indirect illumination

• Often possible to see minute objects or filaments, specially in the aqueous

• Reveals subtle areas of corneal thinning.


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Van Herrick’s Technique : • Used to evaluate anterior chamber angle without

gonioscopy • Narrow slit beam close to limbus with Illumination angle

60° • Medium magnification

Principle : • Compare the width of cornea seen by optical section with the

dark section seen between ant. surface of iris & back of cornea

Interpretation : Grade 4 – open anterior chamber angle 1:1 ratio Grade 3 – open anterior chamber angle 1:2 ratio Grade 2– narrow anterior chamber angle1:4 ratio Grade 1– risky narrow anterior chamber angle less than 1:4 ratio Grade 0– closed anterior chamber

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Van Herrick’s Technique : to assess anterior chamber angle


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Filters : • White filter

• Overview of ocular surface tissues • Examining intraocular structures

• Cobalt blue filter • Coneal abrasion, ulcer • Applanation tonometry

• Red free filter • Rose-bengal staining

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Applanation Tonometer :

The Goldmann Applanation Tonometer is the most common tonometer that usually mounted on the standard slit-lamp biomicroscope.

It’s easy to use and measure the IOP of a seated patient with high accuracy in most clinical situations.

Parts :

1. Tonometer tip (biprism)

2. Metal rod

3. Tonometer housing

4. Force adjustment knob

Associated instruments :

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Principle :

• Applanated force (AF) equals the intraocular pressure (IOP)

• diameter of the applanated area: 3.06 mm here counteracting forces of corneal rigidity and capillary attraction cancel each other

Application :

• Measurement of intraocular pressure (IOP)


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Procedure : 1. Proper positioning of the patient

2. Instill topical anesthetic and flurescein in pt.‘s eye

3. Place the cobalt blue filter with broad slit illumination at 60-90° angle

4. The dial is preset between 1 and 2 (i.e. 10–20 mmHg)

5. Prism is advanced until it just touches the apex of the cornea

6. Viewing into the oculars a pattern of two semicircle will appear which represent the fluorescein-stained tear film touching the prism


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Procedure : 7. Then gently rotate the force

adjustment knob of tonometer to align the inner margins of the semicircles

8. The reading on the dial, multiplied by 10, gives the IOP. Modern digital display system provides actual reading without multiplication

9. Repeat the procedure for other eye

10. At last wash B/E with antibiotic eye drop


Video clip : GAT

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Fundus Observation and Gonioscopy :

• Different types of Contact and Non-contact lenses used for examination, diagnostic and therapeutic purpose in fundoscopy and gonioscopy

• With classic three mirror Goldmann lens post. Segment and irido corneal angle can examined simultaneously

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Fundoscopy :

Contact Glasses :

• Additional tool for fundus observation with the slit lamp

• Mostly direct; erect and non mirrored image of the fundus

• Required :

• dilated pupil

• use of coupling liquid (Hypromellose 0.3%)

• Coaxial angle (0°)

• Illumination – low with 2-4 mm slit

• Magnification – 10-16 x

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Non-contact lenses :

• Additional tool for fundus observation with the slit lamp

• Mostly indirect; upside-down and mirror image of the fundus (convex optics)

• non contact

Required: • dilated pupil

• Coaxial angle (0°)

• Illumination - low with 2-4mm slit

• Magnification – 10-16 x

Fundoscopy :

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Fundus view through 90D non-contact lens :

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Goldmann 3-Mirror gonioscopic lens :

• Procedure same as contact fundus lens

Observation :

• Central lens (0) : Posterior pole

• 73° mirror (1) : Equator

• 67° mirror (2) : Ora serrata

• 59° mirror (3) : Iridocorneal angle

Gonioscopy :

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Application :

• Grading of A/C angle width (Shaffer system)

• Peripheral anterior synechiae

• Neovascularization

• Hyperpigmentation

• Trauma

Angle recession

Trabecular dialysis


Foreign bodies

• Blood in the Schlemm canal

Gonioscopy :

Fig.: Shaffer system grading

Fig.: Blood in chamber angle

Fig.: Neovascularization

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• Slit-lamps have the capability of providing laser delivery with a conjunct laser system installed on it

• Lasers are used for the treatment procedures like photocoagulation, iridotomy or capsulotomy

• Commonly delivered lasers – Nd:YAG

Laser delivery system with slit-lamp :

Fig.: Laser system mounted Slit-lamp

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The slit lamp is one of the most commonly used and valuable diagnostic instruments

for an ophthalmologist of today.

So user level care & maintenance is very much important to get optimum performance & long life from it.

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Video clip : Slit-lamp demonstration

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• Clinical ophthalmology A systemic approach - Jack J Kanski - 7th ed.

• OPHTHALMIC OPTICS – Professor M.A. Matin 2nd ed.

• Clinical Optics – Andrw R. Elkington 3rd ed.

• BASIC OPHTHALMOLOGY – Professor Md. Shamsul Haque – 2nd ed.



• Essentials of Ophthalmology – Samar K Basak – 5th ed.

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