The slit lamp is an instrument used to examine the anterior segment of the eye. It provides stereoscopic, magnified views through illumination and observation systems. It is used for detailed examination of the cornea, anterior chamber, iris, and retina. The slit lamp allows for measurement of intraocular pressure and delivery of laser treatments. Examination techniques include diffuse, direct, indirect, and retroillumination to visualize different ocular structures.

1. Slit Lamp
Shubhangi Shukla

2. Slit Lamp
uses-
● it is used for detailed examination of anterior segment. it gives a
stereoscopic and magnified view of the part examined.
● it is required for examination for angle of anterior chamber with
gonioscope.
● measurement of IOP with appalanation tonometer require slit
lamp.
● delivery of laser like YAG ,Argon and diode can be done only
through slit lamp.
● it is used for detailed examination of retina by slit lamp
biomicroscopy.
● vital staining of cornea is observed through slit lamp.

8. Parts of Slit Lamp
It can be divided into 3 parts of slit lamp.
1. Illumination system
2. Observation system
3. mechanical system
1- Illumination system - it consist of a light source that can be moved
away from observation system so that a paticular angle can be made
between illumination system and observation system. this is required
for different techniques of slit lamp examination.
intensity of light source can be increased or decreased as per
requirement by rotating a knob. another knob can change the height
and diameter of light beam. width of light beam can also be changed
via another knob.
halogen light is used in most of the examination.

9. different filters like -
● cobalt blue filter - it is use for fluorescein staining , fitting of rigid gas
permeable contact lens and applanation tonometer.
● Red free filter (green) - it is used for seeing nerve fiber bundle
defects in glaucoma , blood vessels , microaneurysms and
hemorrhages appear dark against a green background.
● vitreous details are seen better with blue or green light as they have
shorter wavelengths and have more scattering properties.
● yellow filter improves contrast as scattering of blue light is no more
there. all these filters can be introduced using a knob.
2- Observation system - it consist of 2 eyepieces. magnification of image
is obtained by multiplying the power of oculars with the power of the
objective lens. magnifications can be changed either by changing the
objective lens or the oculars. this is achieved by flipping a lever located
below the observation system.

11. How to start ?
● focus the eyepiece.
● adjust the headrest.
● positive the fixation target.
● decrease the room illumination.
● start with diffuse illumination.
● use appropriate magnification.
Basic slit lamp examination -
● patient positioning
● Head support unit.
● adjust height of table or chair
● adjust height of chin rest such that patients lateral canthus is aligned
with the mark.
● adjust ocular eyepiece.
● power up
● fixation

12. ● magnification begin with 6 X - 10X magnification .
● focusing.
● special procedures.
● protocol and documentation.

13. Techniques of slit lamp examination -
● diffuse illumination
● direct illumination
● indirect illumination
● retro illumination
1. Diffuse illumination - it is used to examine different
structures of eyeball like -
● eyelid
● cornea
● conjunctiva
● sclera
● iris
● pupil etc

14. it gives general information. A frosted glass or ground glass is placed
in front of the focused light beam to get diffuse illumination.
magnification is kept low and incident light is projected into the eyeball
obliquely at an angles of 45 degree.

15. 2. Direct illumination - viewing of structures within the focused light beam is known
as direct illumination. it may be of different type -
● optical section - light beam is in form of a slit. it is projected obliquely. the
angle between the oculars and observation system is 30 degree - 60 degree .
more is the angle , wider is the optical section is called parallelepiped. it gives a
cross sectional view of different layers of cornea. lens and anterior part of
vitreous can also be examined in dilated pupil. this technique is applied to locate
corneal lesion, corneal scar , foreign body, depth of AC and type of cataract.

17. ● pinpoint illumination - this technique is used to look for aqueous
flare and cells in AC in uveitis. the room should absolutely dark.
beam is pin point and focused against pupil in the AC. aqueous flare
appears as yellowish particles and cells in AC appear as whitish
reflections.

18. ● specular reflection - it is used to see corneal endothelium. it is best seen with one
eyepiece only. angle of illumination system is set equal to the angle of the oculars
and illumination beam is a parallelepiped. first of all corneal surface is focused with
low magnification. move the oculars 20 degree away from illumination source. now
moves the illumination source 20 to 30 degree away and in opposite direction until
a bright mirror like reflection is seen through one ocular. three reflections are seen.
intermediate reflection is focused finely using high magnification and endothelial
cells can be counted.

19. indirect illumination - here structure not with in the focused light beam are observed. it is
of different type.
● proximal illumination - a moderately wide beam of light is focused on the areas
adjacent to the areas of interest. the lesion is observed with scattered light against
dark background.

20. ● sclerotic scatter - lesions within the corneal substance can be seen by this method.
a parallelepiped illumination beam is focused at the temporal limbus. eyepiece is
focused on central part of cornea and illuminated system is set at an angle
between 45 to 60 degree with the observation system. light beam enters corneal
substance from one limbus undergoes total internal reflection and exits from
opposite limbus .

21. Retro illumination - in this techniques light is reflected from iris and retina to
see more anteriorly located structure. it may be different type .
● in direct retro illumination light is focused behind the structure to be seen
and it is angles at 45 degree. corneal opacity appears black against
illuminated background. lenticular opacity appear dark against red glow
of fundus. thus objects that normally appear bright are seen as black in
this technique.

22. ● in indirect retroillumination light is focused in such a way that the
background becomes dark. the structure to be seen should not be in the
pathway of light.
there is another technique called trans-illumination. in this technique iris
surface is tested for passage of light. illumination system and observation
system are positioned coaxially, i.e. click stop position. red glow seen through
iris confirm hole in the iris.