Slit lamp biomicroscopy

DR.NAFIZ MAHMOOD

SLIT-LAMP BIOMICROSCOPY

Resident

Nat iona l Ins t i tu te o f Ophtha lmo logy and Hosp i ta l Bangladesh

WHY SLIT LAMPS ARE SO GREAT

gold standard device.

This is because they provide…Stereoscopic imageVariable illuminationVariable magnificationExcellent image quality

WHY NAME SLIT LAMP

BIOMICROSCOPE

A narrow vertical slit of light is projected on to the eye and permits microscopic examination of living tissues in cross-

section

History

First concept of slit-lamp was introduced by PROF. ALLVAR GULLSTRAND IN 1911

And named as LARGE GULLSTRAND OPHTHALMOSCOPE

SPECIAL FEATURES1. The alignment of viewing & illumination

system - parfocal2.long working distance. 3.allows to carry out certain manoeuveres like

• FB removal from cornea• interpose certain optical devices-

condensing lens, goniolens, Goldmann applanation tonometer

3. Incorporated with prisms

-invert the image vertically and

horizontally -so it appears erect and right

way round

4. A bank of Galilean telescopes of different

powers

- to allow the magnification

WHAT CAN WE USE THEM FOR?

Routine examination of anterior segment

Problem-based examination of anterior segment

Assessment of anterior chamber depth and angle

Contact lens examination

GonioscopyFundoscopyOcular photographyContact tonometry

(Goldmann)Laser

photocoagulation

On their own

With accessories

BASIC DESIGN

Observation system

Illumination system

Mechanical support system

OBSERVATION SYSTEMcomposed of 2 lenses

- objective lens- eyepiece lens

Objective lens :consists of 2 plano-convex lenses

providing a composite power of +22 D

Eyepiece lenses :magnification : 10×, 16×, 25×provide good stereopsis as the tubes

converged at an angle of 10°- 15°

Prisms :to overcome inverted image produced

by compound microscope

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Fo FoO Fe Fe

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Optics of compound microscope

Cross-section of observation system of

modern slit-lamp

MAGNIFICATION

• Slit lamps provide variable magnification• Lower magnifications - general

assessment and orientation• Higher magnifications -detailed

inspections of areas of interest• There are several ways to do this

- Common methods: Littmann-Galilean telescope and zoom systems- Less common methods: Change the eyepieces and/or change the objective lens

LITTMANN-GALILEAN TELESCOPE METHOD

• A separate optical system is placed in between the eyepiece and the objective

• Utilizes Galilean telescopes to alter magnifications

• It consists of a rotating drum that houses Galilean telescopes

Galilean telescopes consist of a positive and negative lens that provide magnification

based on the lens powers

Galilean magnification changer (G) is placed between the slit-lamp objective (O) and the relay lens ( R ).

ILLUMINATION SYSTEM

Comprises of :• Light source: halogen

lamp• Condenser lens system• Slit and other diaphragms• Filters• Projection lens• Reflecting mirror

MECHANICAL SUPPORT SYSTEM

Consists of :Joystick arrangementUp and down movement

arrangementPatient support arrangementFixation targetMechanical coupling

Technique of biomicroscopy

A.Patient adjustment :should be positioned comfortably in

front of slit-lamp with his or her chin resting on the chin rest and forehead opposed to head rest

B. Instrument adjustment :

- height of the table housing the slit-lamp

should be adjusted according to patient’s

height

- microscope and illumination system

should be aligned wth patient’s eye to be

examined

- fixation target should be placed at

required position.

C. Beginning slit-lamp examination : some points to be kept in mind

I. Room should be semi-darkII. Diffuse illumination – used for short timeIII.Medications like ointments and anaesthetic

eyedrops produces corneal surface disturbance which can be mistaken for pathology.

IV.Low magnification should be 1st used to locate pathology and then higher magnification to examine it.

Structures to see through slit-lamp

External : brow, nose, chick

Lid & lashConjunctiva & sclera

CorneaAnterior chamber

IrisLens

Anterior vitreous

PRINCIPAL OF ILLUMINATION

DIFFUSE ILLUMINATION1

DIRECT FOCAL ILLUMINATION2

SPECULAE REFLECTION3

TRANSILLUMINATION / RETROILUUMINATION4

INDIRECT LATERAL ILLUMINATION5

SCLEROTIC SCATTER6

DIFFUSE ILLUMINATION

LIGHT : Full height Broad beam Low brightness

DIRECTION : Temporally or Nasally

What structures can be seen

White light

Eye & adnexa

Cobalt blue filter with fluorescein1.Evaluation of fluorescein dye ( appear

yellow) staining the ocular surface tissue

2.Tear film3.To discern the fluorescein pattern in

Goldmann Applanation Tonometry

[thin marginal tear meniscus and inferior punctate erosions stained with fluorescein ]

Red free filter with rose bengal dye

Diffuse illumination with red free filter to enhance visibility of rose bengal red dye which has stained

keratin in intraepithelial ( squamous ) neoplasia

DIRECT FOCAL ILLUMINATION

Lamp Microscope

The light and the microscope are both pointed at the object of interest

Beam :full height medium widthmedium bright

Direction:obliquely

Aim :to focus it on cornea so that

quadrilateral block ( parallelepiped) illuminates the cornea

ANTERIOR SURFACE

CROSS-SECTIONAL ILLUMINATION

ANTERIOR SURFACE

CROSS-SECTIONAL ILLUMINATION

POSTERIOR SURFACE

Use :1. to examine the anterior surface &

posterior surface of cornea 2. examination of anterior segment &

lens3. for grading of cells & flares ( when the

height of the beam is reduced to 2-4 mm)

OPTICAL SECTION :when the beam made so narrowed that the anterior & posterior portion becomes very thin leaving only cross sectional illumination of cornea.

Optical section: mostly depth

SPECULAR REFLECTION

i r

lamp microscope

Beam :medium – narrow ( must be thicker than

optical section )

Angle between light & microscope : 50° – 60°

Purpose :• to observe corneal endothelium.

Careful focusing can bring up

endothelial cells, like mosaic pattern

RETROILLUMINATION

Lamp Microscope

An object of interest is lit by retro-illumination when the light source is

directed onto another structure (deeper) so that the reflected light must pass

through that object.Retroillumination of fundus is best performed with -• dilated pupil• viewing and illuminating arm not

parfocal

What can be seen• Blood vessels of cornea, • abnormalities of post. surface of cornea• Cataract & PCO• iris atrophy

Directly illuminate

dRetro-illuminated

Blood vessels of cornea, other abnormalities of post. surface of cornea

INDIRECT LATERAL ILLUMINATION

DIRECTION : • Light is directed just to the side of lesion

to be examined• Some of the light enters the lesion so it

glows internally

What can be seen:

• corneal infiltrates• corneal microcyst• corneal vacule

SCLEROTIC SCATTER

BEAM :medium width

Direction :on to the limbus - temporallythe viewing system focused to center of

cornea

lamp

microscope

Sclerotic scatter produces a diffuse glow of limbus and a backlighting of any corneal opacities, as with cornea verticillata( whorl-like changes) secondary to epithelial

deposition of the oral drug amiodarone

PITFALLS & POINTERS1. Remember to set the oculars to your

refractive error or to plano if you are using spectacles.

2. Proper positioning of the patient3. Intensity of the light at level of patient’s

comfort4. To take advantage of full value of slit-

lamp, examiner must become skilled in using all of the methods of illumination and understand when each is best employed.

Thank you