Overview of ophthalmic examination using slit lamp microscope

1. +
Slit Lamp Biomicroscopy
Dr. Mark Davies
Principal Lecturer

2. +
Session Format
 Overview of instrument
 Basic design
 Slit lamp features:
 Magnification
 Illumination
 Examination techniques
 At the slit lamp:
 Patient set up
 Sequence
 Lid eversion & examination of fornices
 Removal of corneal & subtarsal FB’s
 Questions?

3. +
Overview of Instrument
 The Slit Lamp Microscope (SLM) is the ideal tool for
the assessment of the anterior* segment of the eye
 It provides:
 Excellent image quality
 Flexible magnification (6-40x)
 A stereoscopic view
 Variable illumination
 A stable platform (FB removal etc.)
* Posterior pole may be visualised with additional lenses

4. +
Basic Design
Light Tower
• Variable size, shape, colour &
brightness
• Slit size, shape, and filter
controls
Viewing Arm
• Biomicroscope
• Adjustable eyepieces
• Magnification selector
Central Pivot
• Viewing arm & light source
pivot around this point
• 180 degree arc
• Both focus at same point
(parfocal)
Joystick Control
• Position and focus control

5. +
Slit Lamp Features - Magnification
 Variable setting available
 Lower mag (10x) for
general
examination/orientation e.g.
 Lids, lashes fornices
 Higher mag (16x-40x) for
detailed inspection of ocular
structures e.g.
 Cornea, anterior chamber,
lens
 Dial/flip lever to change
magnification level

6. +
Slit Lamp Features - Illumination
 Light tower produces a slit
beam
 Variable:
 Intensity
 Height
 Width
 Orientation
 Filters:
 Red Free
 Cobalt Blue
 Heat Reduction
 Diffuser

7. +
“It’s all about the slit…”
 A good slit must be:
 Bright
 Evenly illuminated
 Brightly focused
 Have well-defined straight edges
 Illumination should also provide good colour
rendering:
 To discriminate any pathological changes

8. +
Slit Height
 Variable:
 Approx. 0-8 mm
 This graduation allows
measurement e.g.
 Corneal abrasion
 Hypopyon/Hyphaema in AC
 Tall slits are used to view
structures anterior to lens
 Shorter slits for lens
/posterior pole:
 Also useful for anterior
chamber examination

9. +
Slit Width
 Narrow slits can slice
through layers of the
cornea:
 Depth of corneal
abrasions
 Endothelial disorders
 Wide slits are used to
grossly inspect
surfaces:
 Fornices
 Tear film integrity

10. +
Slit Orientation
Rotate lamp housing to achieve effect

11. +
Examination Technique
 Direct illumination:
 Wide Beam
 Parallelepiped
 Optical section
 Indirect illumination:
 Retro-illumination
 Sclerotic scatter
 Combination of the above

12. +
Direct Illumination
Light
Source Microscope
Light source &
microscope both
pointing at area
of interest

13. +
Direct Illumination
 Several forms – classified simply by width of slit:
 Diffuse
 Wide Beam
 Parallelepiped
 Optical Section
 Slit size/shape significantly affects what may be visualised:
 Diffuse/wide beam for overall view
 Wider parallelepiped for broad view of a single plane / narrow
for a more balanced view
 Optical section will ‘cut through’ structure giving thickness &
depth

14. +
Effect of Slit Width
Wide Beam – Mostly
Surface
Parallelepiped – Balance
of Surface & Depth
Optical Section – Mostly
Depth

15. +
Importance of Illumination Angle
 Wider angles allow:
 Accurate visualisation of
deeper layers
 Estimation of depth
 Better perception of
texture
 Both direct and indirect
illumination
simultaneously

16. +
Effect of Angle
450 - Balance of Surface &
Depth
50 - Mostly Surface 850 – Depth Only

17. +
Direct Illumination – Wide Beam
 Use in combination with
low magnification
 Useful for examining:
 Lashes & lid margins
 Lachrymal apparatus
 Upper & lower fornices
 Overall corneal integrity
& TFBUT

18. +
Direct Illumination – Parallelepiped
 Default approach to
corneal inspection
 Shows a block of tissue in
3-D
 Good balance between
surface and depth
 Beam approx. 2mm wide
 Medium to high
magnification

19. +
Optical Section
 Allows judgment of
thickness & depth
 Use:
 Narrowest slit possible
 Largest angle possible
 Highest intensity light
 Dark room
 Sharp focus paramount

20. +
Indirect Illumination
Light
Source Microscope
Object illuminated
indirectly by being
lit from scatter of
light posteriorly

21. +
Indirect Illumination
 Light reflected back from two main sources:
 Iris (backlight the cornea)
 Fundus (backlights the lens)
 Opacities appear dark against a bright background
 Decoupling may sometimes be necessary

22. +
Retroillumination

23. +
Patient Set Up
 Patient chin on bar and
forehead on plastic strap
 Ensure eyes are level with
marker on headrest
 Lamp table at the correct
height for both you and the
patient
 Not too bright!
 Patients have a tendency to
drift away from the
headband during
examination

24. +
Sequence
 Lids & lashes
 Lid eversion (if
indicated)
 Conjunctiva & cornea
 Anterior chamber
evaluation
 Iris
 Lens

25. +
Lid Eversion & Examination of
Fornices
 Brief patient
 Ask patient to look down &
press their forehead on
headband
 Grasp lashes
 Press against tarsal plate of
upper lid with stiff object
 Cotton wool bud
 Minims eye drops
 Flip!
 Traction on lid whilst performing
examination

26. +
Removal of Superficial Ocular
Foreign Bodies I
 Always formally test vision
 History precedes examination*
 Cannot visualise FB? Consider fluorescein staining
 Instil topical anaesthetic
 Soak tip of cotton bud with topical
 Many subtarsal and corneal FB’s can be ‘flicked off’ with
a cotton bud
 Use a ‘rolling’ action and very gentle pressure
*Notwithstanding chemical injury

27. +
Removal of Superficial Ocular
Foreign Bodies II
 Be wary of central corneal FB’s
 Penetrating FB?
 History
 Peaking of Iris
 Siedel Positive
 More recalcitrant corneal FB’s can be gently ‘flicked
off’ with a 26g (orange) cannula:
 Flat of bevel flush against corneal surface
 DO NOT dig cannula into cornea (average corneal
thickness 550 μm)
 Patients should return in 24-48 hours for removal of
rust ring

28. +
Slit Lamp Biomicroscopy
 In Summary:
 Practice & become
familiar with equipment
 Approach examination
in a systematic manner
 If in doubt, seek further
advice from eye unit
 Any Questions?