SLIT LAMP BIOMICROSCOPY

SLIT LAMP

The routine method of examining the outer segment of the eye is with a

slit lamp. It consists of a relatively low-powered binocular compound

microscope which is linked to an adjustable light source.

The instrument is known as a slit lamp because in everyday use the

illumination is arranged so that a narrow vertical slit of light is projected

on to the eye.

INTRODUCTION

Biomicroscope derives its name from the fact that it enables the

practitioner to observe the tissue of eye under magnification.

It not only provides magnified view of every part of eye but also

allows quantitative measurements and photography of every part

for documentation.

BIOMICROSCOPE  Forehead rest

 Canthus alignment

Chin rest

Chin rest adjustment knob

 Fixation light

 Oculars

 Magnification

 Joystick

Slit lamp facilitates the examination of following structures of the eye:

• Eyelid

• Cornea

• Sclera

• Conjunctiva

• Iris

• Aqueous

• Natural crystalline lens and

• Anterior vitreous.

ILLUMINATION SYSTEM

It consist of:

A bright source of light with a slit mechanism

Provides an illumination of 2*10^5 to 4*10^5 lux.

The beam of light can be changed in intensity, height, width,

direction or angle and color during the examination.

Condensing lens system:

•Consist of a couple of planoconvex lenses with their

convex surface in apposition.

Slit and other diapharm:

Height and width of slit can be varied by using knobs.

Reflecting mirrors and prisms

Filters

oYellow filter

oRed free filter

oDiffuser

oCobalt blue filter

OBSERVATION SYSTEM Observation system is essentially a compound microscope composed of two

optical elements

1. an objective,

2. an eyepiece

It presents to the observer an enlarged image of a near object.

The objective lens consists of two planoconvex lenses with their convexities

put together providing a composite power of +22D.

Microscope is binocular i.e. it has two eyepieces giving

binocular observer a stereoscopic view of eye.

The eye piece has a lens of +10D.

To overcome the problem of inverted image produced by

compound microscope ,slit lamp microscope uses a pair of prisms

b/w the objective and eyepiece to reinvert the image.

Magnifications available are 5X, 16X, 25X, 40X and 100X.

MECHANICAL SYSTEM Joystick arrangement

• Movement of microscope and illumination system towards and away from

the eye and from side and side is achieved via joystick arrangement.

Up and down movement arrangement

•Obtained via some sort or screw devices.

Patient support arrangement

•Vertically movable chin rest and the provision to adjust height of table.

Magnification control :

Including two or pair of readily changeable objective

lenses and two sets of eyepieces.

An on and off switch and illumination control .

FILTERSCobalt blue filter

• Used in conjunction with fluorescein stain

• Dye pods in area where the corneal epithelium is broken or absent.

The dye absorbs blue light and emits green.

Uses:

Ocular staining

RGP lenses fitting

Tear layer

Red free (green)filter:

• Obscure any thing that is red hence the red free light , thus blood

vessels or hemorrhages appears black.

• This increases contrast ,revealing the path and pattern of inflamed

blood vessels.

• Fleischer ring can also be viewed satisfactorily with the red green

filter.

Diffuser

Some instruments have a diffuser which is a frosted glass or

a plastic that flips in front of the illuminator. The diffusor

scatters the light, causing an even spread of light over the

entire ocular surface.

TECHNIQUES/METHODS OF ILLUMINATION

DIFFUSE ILLUMINATION Used for gross survey of the eye. After looking for gross pathology the area of

interest can be focused.

i. Light at 45 degrees

ii. Microscope straight

iii. Least illumination/cobalt blue/red free/diffuser

iv. Least magnification

v. Full width Beam

DIRECT ILLUMINATION Involves placing the light source at an angle of about 40-50 degree

from microscope.

This arrangement permits both light beam and microscope to be

sharply focused on the ocular tissue being observed.

Wide beam direct illumination is commonly used as a preliminary

technique to evaluate large area.

The direct illumination examination is carried out utilizing four slit

beam effects on the transparent structures of the eye i-e

1. Optical section

2. Parallelepiped of cornea

3. Conical beam effect

4. Specular reflection

1. OPTIC SECTION Optic section is a very thin parallelepiped and optically cuts a very thin slice

of the cornea.

Angle between the illuminating and viewing path is 45 degree.

With narrow slit, the depth and portion of different objects (Penetrating

depth of foreign bodies, shape of lens etc.) can be resolved more easily.

With wider slit their extension and shape are more visible.

Magnification: Maximum.

Used to localizeBlood vessels

Nerve endings

Cataract

AC Depth

PARALLELEPIPED 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).

Beam angle: 60°, variable  

Beam height: variable, but usually set to maximum

Illumination: low to moderate

Magnification: low to medium

All-purpose evaluation: most commonly used to evaluate almost

every structure.

Cornea: edema, epithelium, endothelium, neovascularization

Lens: cataract

CONICAL BEAM

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.

Produced by narrowing the vertical height of a parallelepiped to

produce a smaller circular or square spot of light.

Light source is 45-60 degree temporally and directed into the pupil.

Biomicroscope directly in front of the eye.

Magnification High (16-25X)

Intensity of light highest.

To see AC for cells and flare

FOCUSING

Beam is focused between the cornea and the anterior lens and the

dark zone between the cornea and the lens is observed.

SPECULAR REFLECTION Established by separating the microscope and slit beam by equal angles from

normal to cornea.

Position of illuminator about 30 degree to one side and the microscope 30

degree to others ide.

Angle of illuminator to microscope must be equal and opposite.

Angle of light should be moved until a very bright reflex obtained from

corneal surface which is called zone of specular reflection.

Under specular reflection anterior corneal surface appears as white

uniform surface and corneal endothelium takes on a mosaic pattern.

Used to observe:

Evaluate general appearance of corneal endothelium

Lens surfaces

Corneal epithelium

SurfaceEndothelium

SCLEROTIC SCATTER

Light beam is focused at the limbus because of total internal

reflection rays of light pass through the substance of cornea and

illuminate the opposite side of limbus.

If there is any pathology like corneal opacity it become visible

because it scatter rays of light.

Used to observe:

Central corneal epithelial edema

Corneal abrasions

INDIRECT ILLUMINATION The beam is focused at an area adjacent to the ocular tissue to be observed.

PROXIMAL ILLUMINATION

Use a parallelepiped beam sharply focused on the given structures like cornea.

The light passes through the cornea and falls out of focus on the iris. The dark

area lateral or proximal to the parallelepiped is the indirect or proximal zone of

illumination.

RETROILLUMINATION

The light is reflected off the deeper structures like the iris or the retina, while

the microscope is focused to study the more anterior portions of the reflected

light.

IRIS RETROILLUMINATION = CORNEA ( Keratic precipitates)

RETINA RETROILLUMINATION = LENS (Cataract) AND CORNEA

BASIC SLIT LAMP EXAMINATIONPatient positioning:

•Head support unit

•Adjust height of table or chair

•Adjust height of chin rest such that patients lateral

canthus is aligned with the mark.

Adjust ocular eyepieces:

•Power up

•Fixation

•Magnification : begin with 6x -10x magnification

•Focusing

•Special procedures

•Protocol and documentation

USES

1. Diagnostic:

•OCT

•FFA

•Anterior segment and posterior segment diseases.

2. Procedures:

Applanation

Tear evaluation

Gonioscopy

Contact lens fitting etc.

3.Therapeutic:

•Laser

•Foreign Body removal etc.

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