SLIT LAMP EXAMINATION
By Dr.Pragnya Rao
Contents • Introduction• Parts of slit lamp• Slit lamp examination• Illumination techniques
1)diffuse
2)direct:
-beam
- tangential
-pinpoint
- specular
3)indirect
- proximal
- sclerotic scatter
- retroillumination
- transillumination• Special procedures
Introduction • Slit lamp is an instrument giving a binocular observer a
sterioscopic observation of the eye, helping in determination
of location of abnormalities with precision Biomicroscope
• Eye can be scanned horizontally and anteroposteriorly.
• Optically -homogenous media appear black.
- cornea, lens and suspended particles in aqueous scatter light opalescent
• Magnification= power of oculars x power of objective lens.
Parts
• Parts: - illuminating arm
- observing limb
- supporting apparatus
Horizontal verticalilluminating source illuminating source
Slit lamp examination
• Patient positioning:
- lock the slit lamp away from head support unit.
- pull the tonometer arm away .
- reassure and instruct the patient to place his chin on chin rest and
forehead against the bar.
- teeth together and breathe through nose.
• Fixation: to keep eyes steady
can use a fixation device
ask to look over examiners ear or shoulder.
• Magnification : initially 6x or 10 x magnification
can use 16x if more closer examination is warranted
• manipulation of light source:
one hand is kept on light source to change beam width, angle, and height
other hand on joystick for position change.
Suggested Power• 6X or 10X: external (lids, conjunctiva), contact lenses• 16X angles, cornea, lens, foreign bodies, corneal abrasions• 40X corneal endothelium
Beam Width• narrowest : angles, cornea, anterior chamber• a bit wider : cornea, lens, etc• a bit wider yet : external, contact lenses• full width : external, applanation tension (with blue filter)
Beam Height• full : most areas and structures• short : checking anterior chamber for cells & flare
Color/Filter• White: most areas and structures
• Blue (with fluorescein dye) applanation tensions, corneal staining,
tear film, staining patterns of rigid contact lenses
• Green (red-free) : evaluating blood vessels, iron lines
Illumination techniques
Categories of illumination
1) Diffuse
2) Direct
3) Indirect.
• Diffuse illumination: provides an even light over the entire ocular surface.
• Direct illumination: light is shone directly onto the area or structure of interest.
• Indirect illumination: object of interest is illuminated by light that is reflected off of another structure.
Illumination techniques
1. Diffuse
2. Direct• Beam• Tangential• Pinpoint• Specular
3. Indirect• Proximal• Sclerotic Scatter• Retroillumination• Transillumination
Diffuse illumination
• Light is spread evenly over the entire observed surface.
• permits a gross survey of the eye (especially the skin).
the beam is opened all the way & light is directed onto the eye at a 450.
• Least amount of magnification available (6X or 10X) is used.
• Observe: eyelids, lashes, conjunctiva, sclera, pattern of redness, iris,
pupil, gross pathology, and media opacities
Diffuse illumination
Direct illumination Beam observing the configuration and densities of opacities, lesions,
and other abnormalities. • Must be used in conjunction with indirect techniques
• Sweep the cornea or other structures with a narrow full-length beam
with microscope directed straight (may also be moved to an angle opposite the illuminator)
• The greater the angle between the illuminator and the microscope, the greater the width of the illuminated section.
• very narrow beam (optical section) directed onto the cornea corneal shape, elevation, and thickness.
• Observe: cornea, iris, lens, vitreous
Focal broadbeam illumination
Focal slit beam
Tangential illumination: • useful in observing surface texture.
• light projected from an oblique angle(Tangential)creates
shadows highlight surface irregularities
• medium-wide beam of moderate height is swung to the side at an oblique• angle (almost parallel to viewed structure) with microscope pointing
straight ahead.
• Magnifications of 10X, 16X, or 25X are used.
• Iris without dilation• Cornea and lens with dilation
• Observe: anterior and posterior cornea, iris, anterior lens.
Tangential illumination
Pinpoint (Conical Section)• to detect suspended particles in AC in liquid media
(Tyndall’s phenomenon)
• Direct the beam so that it enters the cornea temporal to the pupil
to strike iris nasal to the pupil .
• Increase magnification to 16X or 25X. Focus in the anterior chamber between the lens and corneal endothelium.
• Cells (immune cells) and flare (clumps of protein) may be present in the aqueous.
• is easier if pupil is not dilated.
• Observe: cells, flare
Aqueous flaregrade Flare(2mm height, 1mm width)
Cells per field(2mm height, 1mm width)
0 absent 0
1+ Faint,barely detectable 5-10
2+ Moderate,iris and lens details clear
10-20
3+ Marked,Iris and lens details hazy
20-50
4+ Intnse flare,Fibrinous exudates
>50
Specular Reflection• used to visualize the integrity of the corneal and lens surfaces.
• If the surface is smooth reflection is smooth and regular; • surface is broken or rough reflection is irregular/appears textured.
• Position: illuminator & microscope are about 30 degrees on either side of central perpendicular.
• The angle of the illuminator to the microscope must be equal and opposite
• Direct relatively narrow beam onto cornea and reduce height of beam(to reduce glare.
• Best viewed uniocularly.• Observe: corneal epithelium & endothelium, lens surface
Indirect illumination• Structure to be viewed is lit up by light reflected off uninvolved
area
Proximal indirect illumination:• used to observe internal detail, depth, and density.
• short,fairly narrow slit beam is placed at the border of the structure or pathology
• (The light will be scattered into the surrounding tissue, creating a light background that highlights the edges of the abnormality.
Observe: corneal opacities (edema, infiltrates, vessels, foreign bodies), lens, iris
Proximal indirect illumination
Sclerotic Scatter
• Indirect form of illumination created by decentering the beam
after releasing the central locking screw
• Broad beam is directed to temporal limbus
• Light is reflected through thickness of cornea to reflect onto opposite limbus,highlighting opacities in central cornea.
• .
• 10X magnification, with the microscope directed straight ahead.
• iris provides a contrasting dark background.
• Observe: general pattern of corneal opacities
Retroiilumination • The light strikes the object of interest from a point behind the
object and is then reflected back to the observer
Direct Retroillumination From the Iris• Used to view corneal pathology. • moderately wide slit beam is aimed toward the iris directly behind the
corneal abnormality.
Indirect Retroillumination From the Iris• the beam is directed to an area of the iris bordering the portion of the iris
behind the pathology • This provides a dark background, allowing corneal opacities to be viewed
with more contrast.• The angles are also evaluated with this technique
• Retroillumination from the Fundus (Red Reflex)
• The light is directed so that it strikes the fundus and creates a
glow behind the abnormality
Highlights media opacities( cataracts, corneal scars)
• The slit beam and microscope must be nearly coaxial;
• Shorten the beam to the height of the pupil to avoid reflecting the bright light off of the iris.
• This view is with pupil dilated.
• Observe: cornea, lens, vitreous
Transillumination
• a structure is evaluated by how light passes through it.
Iris Transillumination
• The pupil must be at mid mydriasis (3 to 4 mm when light stimulated) and light source coaxial with the microscope.
• Use a full circle beam of light equal to the size of the pupil with microscope focussed on iris.
• Observe: iris defects (they will glow with the orange light reflected from the
fundus)
Applanation tonometry• Principle: Imbert- Fick principle
amount of force needed to flaten/applanate a known area of
cornea.
IOP is - directly proportional to pressure applied
- inversely proportional to area flattened
7mm of flat plexiglass plate flattens an area of 3.06mm in diameter at posterior corneal surface.
Most accurate reading is obtained when the inner surface 2 mires
coincide
Gonioscopy
• Observation of angle of anterior chamber by diverting the light beams using gonioscopes
• Slit lamp enables stereoscopic observation of the eye
• Parts: biomicroscope
illuminating arm
supporting apparatus
• Illumination techniques: diffuse,direct, and indirect
References
• The slit lamp primer• Parson’s diseases of the eye
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