The document provides an overview of slit lamp biomicroscopy. It describes the basic design of the slit lamp microscope including the light tower, viewing arm, and central pivot. It discusses the slit lamp features of magnification, illumination, and examination techniques using direct and indirect lighting. The document outlines the proper procedure for patient setup and examination sequence, including lid eversion and removal of superficial ocular foreign bodies.

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Slit Lamp Biomicroscopy
Dr. Mark Davies
Principal Lecturer

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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?

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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

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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

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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

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

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“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

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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

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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

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Slit Orientation
Rotate lamp housing to achieve effect

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

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

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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

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

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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

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

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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

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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

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

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

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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

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Retroillumination

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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

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

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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

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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

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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

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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?