Slit lamp biomicroscopy

OP1201 – Basic Clinical Techniques Part 1 Dr Kirsten Hamilton-Maxwell


Slit lamp biomicroscopy. OP1201 – Basic Clinical Techniques Part 1 Dr Kirsten Hamilton-Maxwell. Today’s goals. By the end of today’s lecture, you should be able to… List the uses of the slit lamp biomicroscope - PowerPoint PPT Presentation

Transcript of Slit lamp biomicroscopy

Page 1: Slit lamp biomicroscopy

OP1201 – Basic Clinical Techniques

Part 1

Dr Kirsten Hamilton-Maxwell

Page 2: Slit lamp biomicroscopy

Today’s goalsBy the end of today’s lecture, you should be able

to…List the uses of the slit lamp biomicroscopeIdentify the main components of the slit lamp; be able

to operate these componentsDiscuss and perform a series of basic illumination and

magnification techniquesA second lecture will follow where we talk about

combining these techniques into a routine and look at some examples

Page 3: Slit lamp biomicroscopy

Why slit lamps are so greatSlit lamp assessment is considered to be the gold

standard device for the assessment of the anterior segment of the eye in clinical practice

This is because they provide…Excellent image qualityStereoscopic imageFlexible illuminationFlexible magnification

Therefore there are many different usesEven more when attachments are added

Page 4: Slit lamp biomicroscopy

What can we use them for?On their own With accessories

Routine examination of anterior segmentAdnexa through to anterior


Problem-based examination of anterior segment

Contact lens examination

Assessment of anterior chamber depth and angle



Ocular photography

Contact tonometry (Goldmann)


Corneal sensitivity

measurements (aesthiometry)

Laser photocoagulation

Page 5: Slit lamp biomicroscopy

Basic Design Viewing arm

Biomicroscope Adjustable focus eyepieces Magnification dial

Illumination arm The “slit lamp” Slit size, shape and filter controls Variable size, shape, colour and brightness

Biomicroscope and illumination are mechanically coupled around central pivot point (copivotal)

Both focus at the same point (parfocal) Both arms can swing independently 180º along

horizontal – there is a scale in degrees Both always central regardless of angle (isocentric)

Moveable base plate and joystick control

Page 6: Slit lamp biomicroscopy
Page 7: Slit lamp biomicroscopy

A good biomicroscope has…Adequate working distance between the microscope

and the eye to allow the practitioner to access the eye

Convenient size for use in practiceAdaptable to suit different practitionersGood resolutionGood depth of focusA wide range of magnifications

Page 8: Slit lamp biomicroscopy
Page 9: Slit lamp biomicroscopy

MagnificationSlit lamps provide variable magnificationLower magnifications are used for general

assessment and orientationHigher magnifications are used for detailed

inspections of areas of interestThere 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

Page 10: Slit lamp biomicroscopy

Littmann-Galilean telescope methodA separate optical system is placed in between the

eyepiece and the objectiveIt consists of a rotating drum that house 2 Galilean

telescopes plus a pair of empty slotsOptics refresher: Galilean telescopes consist of a positive

and negative lens that provide magnification based on the lens powers and their separation

It is easy to identify whether the slit lamp you are using has this insideThe magnification dial will click into place as you turn it, and

there will be numbers on the dial that correspond to the magnification in each position

Page 11: Slit lamp biomicroscopy

A Galilean telescopeParallel light enters and exits.Magnification is typically the intended outcome.However, if you look from the other side, the image will be minified.

Page 12: Slit lamp biomicroscopy

Two telescopes produce two magnificationsMag highest when the

convex lens is near objective

Reversal of these two telescopes produces two further minifications

No telescope provides 5th option

Page 13: Slit lamp biomicroscopy

Zoom systemsThis tends to be found on high-end Nikon, Topcon

and Zeiss instrumentsMagnification can vary between 7x to ~ 40XI find that the image quality is not as good with zoom


Page 14: Slit lamp biomicroscopy

Change eyepieces or objectiveEyepieces ObjectiveOften two sets provided with

slit lamp Typical values 10x, 12.5x, 15x or

20xInconvenient so rarely usedGenerally unnecessary on

modern slit lamps

Flip arrangement for rapid change

Usually only two options due to space confinements

Typical values are 1x and 2x


Page 15: Slit lamp biomicroscopy

The slit lamp

Page 16: Slit lamp biomicroscopy

What makes a good slit?A good slit needs to be

BrightEvenly illuminatedFinely focusedHave well defined, straight edgesFlexible in terms of size, shape, colour and intensity

The illumination also needs toProvide good colour rendering to detect subtle colour


Page 17: Slit lamp biomicroscopy

Slit widthContinuously variable (0 to

12-14mm)May be graduated to allow

measurementNarrow slits are used to “slice”

through the cornea to determine depth or thickness

Wide slits are used to inspect surfaces

Page 18: Slit lamp biomicroscopy

Slit heightMay be continuous or set to fixed

heightsUsually a combination of the twoMay be graduated to allow for

measurement Long slits are used to view most

structures in front of the pupil, while short slits pass through the pupil much better

Short slit also used to assess the clarity of the anterior chamber

Page 19: Slit lamp biomicroscopy

Slit orientation Achieved by rotating

lamp housing

Page 20: Slit lamp biomicroscopy

FiltersSlit lamps may have some/all of the following filters

DiffuserHeat reductionNeutral densityPolarisingRed freeCobalt blueWratten (in observation system)

Page 21: Slit lamp biomicroscopy
Page 22: Slit lamp biomicroscopy

Methods of illuminationDirectIndirectRetro-illuminationSclerotic scatter (next year)Specular reflection (next year)Conical section (next year)A combination of these methods is used to view

the anterior eye structures

Page 23: Slit lamp biomicroscopy

Direct illumination


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

Page 24: Slit lamp biomicroscopy

Direct illuminationThere are several different forms, named simply by how

wide the slit isDiffuse (usually not a slit at all)Wide beamParallelepipedOptical section

The slit width will change what you can seeDiffuse/wide beam for an overall viewWide parallelepiped for broad views of one plane (e.g.

Surface of a structure) and narrow parallelepiped for a balanced view

Optical section to “cut through” a tissue, for thickness and depth

Page 25: Slit lamp biomicroscopy

Effect of slit width (cornea)

Wide beam: mostly surface Parallelepiped: balance of surface and depth Optical section:

mostly depth

Page 26: Slit lamp biomicroscopy

Why is the angle importantThe angle between the microscope and the illumination

arms is important. Wider angles…Allow view of deeper layers without interference from

reflections from upper layersThe wider the beam, the greater the angle needed to “see

behind the surface layer”Allows estimation of depthAllows better perception of textureAllows direct/indirect/retro simultaneously

You’ll find a graduated scale located at the pivot point of the two slit lamp armsIt will give you the total separation between the two arms in


Page 27: Slit lamp biomicroscopy

Effect of angle (cornea)

45º: balance of surface and depth

5º: surface only 85º: depth only

Page 28: Slit lamp biomicroscopy

Wide beam/DiffuseUsed for general inspection

of eye and adnexaGood for colour

assessmentContact lens fitWide slit, diffusing inserted,

microscope in front, illumination angle 30–50°, magnification of 6-10xPatients are generally

unable to tolerate the brightness of a wide beam

This eye has iris naevi (freckles)

Page 29: Slit lamp biomicroscopy

ParallelepipedDefault method for

corneal inspectionShows a block of tissue

in 3-D, so good balance between surface and depth inspection

Beam about 2 mm, microscope/illumination, variable angle, medium to high mag (10-25x)

This is a narrow parallelepiped being used to view iris and pupillary margin. The light first passes through the cornea but is out of focus there.

Page 30: Slit lamp biomicroscopy

Optical sectionAllows judgement of

thickness or depthUse the narrowest slit

possible (0.1 – 0.2 mm), angled beam (largest angle possible), high illumination, and a dark room

You need very sharp focus

A helpful tip: Even though this instrument is called a slit lamp, we hardly ever need to use a slit this narrow. Save it for when you need to work out the depth or thickness of a corneal lesion.

Page 31: Slit lamp biomicroscopy


An object being viewed is illuminated indirectly when it lit by reflections/scatter of light that occur when the light is shone other than onto the object itself.

Page 32: Slit lamp biomicroscopy

Indirect illuminationGood for subtle detail, which would be obscured or

washed out by large amounts of illuminationLight internally reflected within the cornea, or reflected by

other surrounding tissueOpacities scatter light so they will appear light in colour

They are best viewed against the dark pupil (or dark iris, if your patient happens to have one)

To achieve the effect, keep the slit width narrow to medium (2-4 mm), and view with a medium to wide angle. Magnification will vary depending on the size and extent of the object, but it’s typically medium to high for subtle defects

Page 33: Slit lamp biomicroscopy

This picture shows a contact-lens related condition called neovascularisation. These are blood vessels in the cornea. In this example, we don’t move anything but our attention – the light and focus stays where it is. We can do this because the slit doesn’t light up our whole field of view

Directly illuminated

Indirectly illuminated

Page 34: Slit lamp biomicroscopy
Page 35: Slit lamp biomicroscopy


An object of interest is lit by retro-illumination when the light source is directed onto another structure so that the reflected light must pass through that object.

Page 36: Slit lamp biomicroscopy

Retro-illuminationLight may be reflected from 2 main structures:

Iris: this back-lights the corneaFundus: this back-lights the lens

Opacities will appear dark against a bright backgroundFor iris retro-illumination, use a narrow-moderate width

slit, a wide angle of illumination, and magnification appropriate to the object size/extentDecoupling may be necessary when the magnification high

For fundus retro-illumination, use a short slit with narrow-moderate width, narrow angle of illumination (0-10º), and moderate magnification

Page 37: Slit lamp biomicroscopy

Directly illuminated

Indirectly illuminated

This is the same example from earlier. The blood vessels in the indicated section are retro-illuminated because they are being lit from behind (the light has reflected off the iris).


Page 38: Slit lamp biomicroscopy

This is an example of retro-illumination of the lens (the light has reflected from the retina). This patient has cortical spokes, which are indicative of early cortical cataract.

Page 39: Slit lamp biomicroscopy

Marginal retro-illuminationAt the border of the zones illuminated by indirect

and retro, therefore viewing technique is similar for retro with high mag, decoupling helps

Objects of higher refractive index show “reversed illumination”

Useful to differentiate microcysts (high refractive index) from vacuoles (low refractive index)

Page 40: Slit lamp biomicroscopy


Page 41: Slit lamp biomicroscopy

Recommended readingElliott, Section 6.61-6.67.

There are lots of examples on Elliott Online (pictures and video)

For section 6.64, parts 2, 3, 4, 5 and 6 only