SLIT LAMP – BIO MICROSCOPY OF EYE

By- Dr. Paresh Vijay NichlaniModerators- Dr. K Srikanth

Dr N Swathi

NEED OF SLIT LAMP ???

Magnified View Stereoscopic view Quantitative measurement

EVOLUTION OF SLIT LAMP Purkinje (1823)- One hand held lamp and one hand held lens De Wecker (1863)- mono-ocular microscope Albert & Greenough (1891)- Binocular microscope Czapski (1897)- binocular corneal microscope Gullstrand (1911)- Illumination system with a slit Henker (1916) – Combined the two Hans Goldmann (1933) – Both the lamp and slit beam with

horizontal and vertical adjustment were placed on single stage, Haag-Streit model

Littmann (1950) - incorporated rotatory magnification changer- galilean teliscopee – zeiss slit lamp

PARTS OF MODERN SLIT LAMP Observation system (Microscope) Illumination system Mechanical system

BRUSHUP • Ray of light passing from optical center will not be refracted.• Rays coming from infinity ( zero vergence ) will converge to focal point• Rays originating from focus will come parallel after refracting

OBSERVATION SYSTEM – MICROSCOPE Based on principle of Keplerian

telescope

OBSERVATION SYSTEM 1. Objective lens – two Plano convex

lens, convexities put together -+22.00 D

2. Eye piece - +10.00 D, Tubes converged at an angle of 10-15 degrees- stereopsis

3. Prisms- rectify problem of inverted image

GALILEAN MAGNIFICATION CHANGER

Based on principle of Galilean Telescope

MAGNIFICATION SYSTEM

Haag Streit magnification system- Grenough typeGalilean Magnification changer

PRINCIPLE OF ILLUMINATION SYSTEM Kohler illumination principle

Converts light source to a beam of homogenous brightness with minimal glare

Advantage is that a very sharp and bright light is obtained

ILLUMINATION SYSTEM1. Light source – nerst lamp > arc lamp >

Mercury vapour lamp > halogen Lamp> LED lampsIllumination – 2*105 to 4*105 lux

2. Condenser lens – coupled Plano convex lens

3. Slit and other diaphragm – horizontal and vertical diaphragm

4. Filters – cobalt blue filter, red free filter

5. Projection lens - diameter of lens is smaller

- Better quality image- Increases depth of focus

of slit – better optical section.6. Reflecting mirror/ prism – illumination axis

do not obstruct field of vision

TYPES – LOCATION OF ILLUMINATION SYSTEM

Zeiss Haag-streit

MECHANICAL SUPPORT SYSTEM

Joystick

Patient support arrangement

Fixation target

Mechanical coupling

TYPES OF ILLUMINATION Depending upon the structures and

there different optical property we use different types of illumination.

1. DIFFUSE ILLUMINATIONSettings

- Slit fully opened (annular diaphragm)- Inserted diffuser- Microscope positioned at 0°-Angle of slit illumination system approx. 30° - 50°-Magnification – 5-12x

Uses- general surveys of anterior eye segments- general observation of the surfacesof crystalline lens and cornea- assessment of the lachrymal reflex-assessment of soft contact lenses-It can be used with filters

Pterygium

2. DIRECT FOCAL ILLUMINATION• Slit beam is regulated until it coincides with exact focus of the microscope• Settings – Narrow slit at oblique angle (30), slit 2-3mm , 5-45x • 3d layered view

- cornea lens and ant. Phase of vitreous disperse light and gets visible against dark back ground.

• This type of illumination can be used with 3 types of different beam

1. Optical Section2. parallelepiped3. conical beam

effect

OPTICAL SECTION A narrow slit is focused obliquely 2-

3mm, 30-45, – knife like histological sections of cornea, lens & ant. phase of vitreous

Optical section of cornea – 1.Tear layer- ant. Most bright zone2. Epithelium- dark line3. Bowman’s membrane – bright line 4. Stroma- Wider granular grey zone 5. Descemet’s membrane – bright zone

Uses – 1. corneal curvature 2. Corneal thickness 3. Location of corneal pathology

4. Van Her-rick method of ac depth

OPTICAL SECTION OF LENS Optical section of lens

1. Ant capsule 2. sub capsular clear zone – c1 3. Bright narrow zone of discontinuity 4.second clear cortical

zone – c2

5.Light scratting zone of deep cortex – c3 6.Clear zone of deep cortex. 7. Nucleus

Parallelopiped – 2-3mm wide focal slit – used for pathologies on epithelial and stroma

Conical beam- small circular beam – examining aqueous for cells and flares – at 45-60 degrees, at high mag.

3 INDIRECT ILLUMINATION Slit beam is focused beside the area

to be observed- The axes of illuminating and viewing path do not intersect at the point of image focus.

Angle-60, variable, slit max height

Uses –1. Corneal infiltrates2. Corneal microcytes3. Corneal vacuoles4. Epithelial cells

4RETRO ILLUMINATION • Light is reflected off from

iris or fundus• system and observation axis

are set to 0°. • it is essential that the pupil is• dilated as otherwise the

resulting relatively small field of view through a normal size pupil makes observation

• almost impossible.

• Direct- Observer is in direct pathway of light reflected from structure. Pathology- against illuminating background.

• Indirect – observer right angled to observing structure. Not in line with light , Pathology – against dark non illuminated background.

GRAVES – PATHOLOGY- OPTICAL PROPERTIES

Obstructive- opaque to light- dark against bright background eg- pigments

Respersive- scatter light but do not obstruct – brightly against dark background epithelial edema, precipitates.

Refrectile- distort view as refrective index is different from surrounding. Eg – vacuole.

5. SPECULAR REFLECTION Reflection accurse – beam of

light incident on optical surface- zone of discontinuity

Observer in path of reflected light – dazzling reflex - specular reflex – dark areas in reflex

Technique – Pt to look 30 degree temporally , light beam focused from opp. side, focused under high magnification, 3-4 mm from limbus- slit is rotated more temporally to about 60 degree (i=r)

Uses – endothelial cell count

6. SCLEROTIC SCATTER

Uses- outline finest corneal pathology

COBALT BLUE FILTER This throws a blue

light, Principle – fluorescence

– these substance absorbs light of a colour and then emit a light of other colour in this case it absorbs blue and emits yellowish green.

Uses – corneal ulcer, scidel test etc, tear BUT etc.

RED FREE FILTER This filter emits green

light – This causes obscure red colour

Blood vessels and haemorrhages appear black

Areas of episclera with lymphocyte appears yellow

Fleischer ring

ACCESSORY DEVICES Gonioscopy Fundus examination using lens Pachymetry Applenation tonometry Slit lamp photography Slit lamp video graphy Slit lamp – argon, diode and yag laser Others

WHAT DO WE KNOW?? WHAT WE HAVE LEARNT??

Evolution of slit lamp Parts of slit lamp Optics of slit lamp Uses Types of illumination Accessory devices

The future- dime illumination coupled with electronic light amplification system