a comprehensive presentation on Slit-lamp in which i have described about the history, optics and also the uses of different illuminations by Dr. Paresh Nichlani

1. SLIT LAMP – BIO MICROSCOPY OF EYE
 By- Dr. Paresh Vijay Nichlani
Moderators- Dr. K Srikanth
Dr N Swathi

2. NEED OF SLIT LAMP ???
 Magnified View
 Stereoscopic view
 Quantitative measurement

3. 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

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

5. 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

6. OBSERVATION SYSTEM – MICROSCOPE
 Based on principle of Keplerian telescope

7. 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

8. GALILEAN MAGNIFICATION CHANGER
Based on principle of Galilean Telescope

9. MAGNIFICATION SYSTEM
Haag Streit magnification system- Grenough typeGalilean Magnification changer

10. 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

11. ILLUMINATION SYSTEM
1. Light source – nerst lamp > arc lamp > Mercury
vapour lamp > halogen Lamp> LED lamps
Illumination – 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

12. TYPES – LOCATION OF ILLUMINATION SYSTEM

13. MECHANICAL SUPPORT SYSTEM
Joystick
Patient support arrangement
Fixation target
Mechanical coupling

14. TYPES OF ILLUMINATION
 Depending upon the structures and there
different optical property we use different
types of illumination.

15. 1. DIFFUSE ILLUMINATION
Settings
- 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 surfaces
of crystalline lens and cornea
- assessment of the lachrymal reflex
-assessment of soft contact lenses
-It can be used with filters

16. Pterygium

18. 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 Section
2. parallelepiped
3. conical beam effect

19. 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 zone
2. Epithelium- dark line
3. 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

21. 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

22.  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.

23. 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 infiltrates
2. Corneal microcytes
3. Corneal vacuoles
4. Epithelial cells

24. 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.

25. • 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.

26. 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.

27. 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

28. 6. SCLEROTIC SCATTER
Uses- outline finest corneal
pathology

29. 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.

30. 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

31. 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

32. 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