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