Slit Lamp Biomicroscopy Intro

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Introduction to Slit Lamp

Biomicroscopy

Edeline Lu, OD

Assistant Professor, SCCO

Slit Lamp Instrumentation

Basic design



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Hardware

Forehead rest

Canthus alignment

Chin rest

Chin rest adjustment knob

Fixation light

Lock for slit lamp base

Table height adjustment

Headrest

Chinrest

Fixation light

Canthus alignment

Chinrest adjustment



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Beam intensity

Slit lamp base lock



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Biomicroscope

Oculars

Convergent optics

Divergent optics

Magnification

Joystick

Vertical control knob



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Biomicroscope

Illumination system On/off

Intensity

Beam height

Beam width

Beam angle

Beam filter:

Neutral density

Red free

Cobalt blue

Click stop



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Beam adjustment

Beam orientation

Beam height

Beam width

Filter selection

Beam angle



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Ancillary attachments

Goldmann applanation tonometer

Anterior segment camera

Laser



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Slit Lamp Biomicroscopy

Types of illumination Direct focal

Diffuse

Parallelepiped

Optic section

Conical beam

Specular reflection

Indirect/proximal

parallelepiped

Sclerotic scatter Retroillumination

direct, indirect

Types of illumination

Direct Focal Illumination

General principle: examiner assesses the

structure in question by looking directly into the

path of the beam of light



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Types of Illumination: Direct

Direct Illuminationat cornea

Adapted from Martonyi, et al.

Direct Illumination

at iris

Types of illumination: Direct Focal

Diffuse Illumination:

gross inspection over a maximum illuminated area

Lids, lashes, lacrimal, conjunctiva



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Diffuse Illumination


Diffuse illumination

Set up

Beam angle: variable

Beam width: 4 mm to maximum

Beam height: maximum

Filter: none

Illumination: low

Magnification: low



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Direct Focal Illumination: Parallelepiped

Definition: beam of light that has two parallel sides

Any beam of light with a width between diffuse and optic

section (usually between 0.5mm and 2.0mm)

Provides a 3-dimensional view (width, height and depth)

Parallelepiped

Adapted from Birinyi



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Direct Focal Illumination: Parallelepiped

Set up

Beam angle: 60°, variable

Beam width: 0.5 mm to 2.0 mm

Beam height: variable, but usually set to

maximum

Filter: none

Illumination: low to moderate

Magnification: low to medium

Parallelepiped

All-purpose evaluation: most commonly

used to evaluate almost every structure

Cornea: edema, epithelium, endothelium,

neovascularization

Lens: vacuoules, cataract, Y-suture



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Direct focal illumination: Optic Section

Definition: slit beam of light used to localize

depth of defects.

Provides a 2-dimensional (height and depth)

view.

Optic Section

Set up

Beam angle: 60° for angle estimation, variable

Beam width: ~0.5mm

Beam height: variable, but usually max

Filter: none

Illumination: moderate to high

Magnification: medium to high



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Optic Section

Uses:

Cornea: to determine depth of lesion

Anterior chamber: to determine depth

Angle estimation

Lens: to determine depth/location/layer

Direct Focal Illumination: Conical Beam Definition: a small round or square beam of light

used to assess the status of the anterior

chamber by oscillating between the cornea and

the lens



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Conical Beam

Set up:

Beam angle: greater than 60°

Beam width: parallelepiped or open

Beam height: 2-4 mm high, or smallest circular

or square aperture

Filter: none

Illumination: maximum

Magnification: high

Conical beam

Uses:

Evaluates anterior chamber for presence of

cells and flare.



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Direct Focal Illumination: Specular

Reflection

Special illumination that judges the quality

of a surface

Angle of incidence of the beam of light

from the slit lamp equals the angle of

reflection of light into the biomicroscope

Only observable through one ocular at a

time

Specular Reflection

Set up:

Beam angle: greater than 45°

Beam width: small parallelepiped


Filter: none

Illumination: high

Magnification: medium to high



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Types of Illumination: Indirect/Proximal Definition: zone of illumination that is adjacent to

the direct focal beam.

Provides a softer, more scattered light to view

abnormalities that would otherwise be washed

out under direct illumination



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Types of Illumination: Indirect/Proximal

Indirect illumination


Indirect/proximal Illumination

Set up:



Beam height: maximum height

Filter: none

Illumination: medium




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Indirect/proximal Illumination

Uses:

Cornea: SEI’s, corneal nerves, scars,

neovascularization

Iris lens

Indirect Illumination: Sclerotic Scatter

Type of indirect illumination in which light

is directed at the limbus to scatter light

internally throughout the cornea

May require examiner to view the cornea

outside of the biomicroscope in the case of

central corneal clouding.



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Sclerotic Scatter

Set up:

Beam angle: 60°



Beam positioned at temporal limbus

Illumination: medium to high

Magnification: low, but usually viewed outside

oculars

Sclerotic Scatter



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Types of Illumination: Retroillumination

Definition: zone of illumination that utilizes light

bounced off another structure

Objects that are opaque to light appear dark (ie, scars,

pigment, blood vessels)

Objects that are clear will appear light (ie, cornea, lens)

Objects that scatter light will appear light (ie, epithelial

edema, vacuoles)

Two types: Direct, Indirect

Usually used for cornea, but can be used for

lens and iris as well.

Retroillumination

Direct Retroillumination:

Zone of illumination that is directly in the path of

the reflected beam of light

Set up:




Filter: none

Illumination: medium




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Direct Retro-illumination


Direct Retroillumination

Uses:

Cornea

Iris: transillumination defects

Lens: Posterior sclerotic cataract



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Retroillumination

Indirect Retroillumination

Zone of illumination adjacent to the reflected

beam of light.

Set Up:




Filter: none Illumination: medium



Indirect Retro-illumination




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Types of Illumination (All)

Direct Illumination

Direct Retro-illumination

Indirect Retro-illumination

Indirect illumination




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Getting Ready to do the Exam

Preparation

Pt education: “I’m going to be using this

instrument to evaluate the health of the front

part of your eye.”

Disinfection:

Clean chin rest, forehead rest

May use tissue for chin rest

Preparation

Parfocal

Bringing the oculars of the biomicroscope into the

same plane of focus as the illumination system of thebiomicroscope.

• Achieving parfocal = light beam is focused at the same

time as the structure in question is focused.



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Parfocaling

Technique: Focus a parallelepiped light beam onto a

focusing/test bar or on the patient’s closedeyelid

Lock slit lamp base

Fog each ocular: turn the eyepiececounterclockwise to most plus

Turn eyepiece clockwise until the parallelepiped

light beam just comes into focus

Repeat with the other eyepiece

Preparation: Alignment

Adjust height of slit lamp and canthus

alignment to optimize patient comfort

Alternative setup:

Children

Obese/well-endowed

Wheelchair-bound

Instruct patient to keep forehead firmly against

forehead rest (teeth together)

Provide a good fixation target



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Troubleshooting

Focusing Problems

Bad technique in parfocaling

Not parfocaled

Forehead falling away from head rest

Chin not firmly against chin rest

Examiner accommodates

Instrument myopia

No view through oculars

Light housing in front of one ocular

Dial turned in between to mag settings

Instrument not on

Instrument not plugged in or becomes loose

Slit Lamp Biomicroscopy Intro

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