1. Slit lamp biomicroscopy
OP1201 – Basic Clinical Techniques
Part 1
Dr Kirsten Hamilton-Maxwell

2. Today’s goals By the end of today’s lecture, you should be able to…
List the uses of the slit lamp biomicroscope
Identify the main components of the slit lamp; be able to operate these components
Discuss and perform a series of basic illumination and magnification techniques
A second lecture will follow where we talk about combining these techniques into a routine and look at some examples

3. Why slit lamps are so great
Slit 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 quality
Stereoscopic image
Flexible illumination
Flexible magnification
Therefore there are many different uses
Even more when attachments are added

4. What can we use them for? On their own With accessories
Routine examination of anterior segment
Adnexa through to anterior vitreous
Problem-based examination of anterior segment
Contact lens examination
Assessment of anterior chamber depth and angle
Gonioscopy
Fundoscopy
Ocular photography
Contact tonometry (Goldmann)
Pachymetry
Corneal sensitivity measurements (aesthiometry)
Laser photocoagulation

5. Basic Design Viewing arm Illumination 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

6. Biomicroscope

7. 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 practice
Adaptable to suit different practitioners
Good resolution
Good depth of focus
A wide range of magnifications

8. Magnification

9. Magnification Slit lamps provide variable magnification
Lower magnifications are used for general assessment and orientation
Higher magnifications are used for 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

10. Littmann-Galilean telescope method
A separate optical system is placed in between the eyepiece and the objective
It consists of a rotating drum that house 2 Galilean telescopes plus a pair of empty slots
Optics 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 inside
The 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

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

12. Two telescopes produce two magnifications
Mag highest when the convex lens is near objective
Reversal of these two telescopes produces two further minifications
No telescope provides 5th option

13. Zoom systems
This tends to be found on high-end Nikon, Topcon and Zeiss instruments
Magnification can vary between 7x to ~ 40X
I find that the image quality is not as good with zoom magnification

14. Change eyepieces or objective
Often two sets provided with slit lamp
Typical values 10x, 12.5x, 15x or 20x
Inconvenient so rarely used
Generally unnecessary on modern slit lamps
Flip arrangement for rapid change
Usually only two options due to space confinements
Typical values are 1x and 2x
Lever

15. Illumination
The slit lamp

16. What makes a good slit? A good slit needs to be
Bright
Evenly illuminated
Finely focused
Have well defined, straight edges
Flexible in terms of size, shape, colour and intensity
The illumination also needs to
Provide good colour rendering to detect subtle colour changes

17. Slit width Continuously variable (0 to 12-14mm)
May be graduated to allow measurement
Narrow slits are used to “slice” through the cornea to determine depth or thickness
Wide slits are used to inspect surfaces
Grading allows measurements of features of interest

18. Slit height May be continuous or set to fixed heights
Usually a combination of the two
May 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
Grading allows measurements of features of interest

19. Slit orientation Achieved by rotating lamp housing
Grading allows measurements of features of interest

20. Filters Slit lamps may have some/all of the following filters Diffuser
Heat reduction
Neutral density
Polarising
Red free
Cobalt blue
Wratten (in observation system)

21. Types of illumination

22. Methods of illumination
Direct
Indirect
Retro-illumination
Sclerotic scatter (next year)
Specular reflection (next year)
Conical section (next year)
A combination of these methods is used to view the anterior eye structures

23. Direct illumination
The light and the microscope are both pointed at the object of interest
Focus light and microscope on same region of interest.
Microscope
Lamp

24. Direct illumination
There are several different forms, named simply by how wide the slit is
Diffuse (usually not a slit at all)
Wide beam
Parallelepiped
Optical section
The slit width will change what you can see
Diffuse/wide beam for an overall view
Wide 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

25. Effect of slit width (cornea)
Wide beam: mostly surface
Parallelepiped: balance of surface and depth
Optical section: mostly depth

26. Why is the angle important
The angle between the microscope and the illumination arms is important. Wider angles…
Allow view of deeper layers without interference from reflections from upper layers
The wider the beam, the greater the angle needed to “see behind the surface layer”
Allows estimation of depth
Allows better perception of texture
Allows direct/indirect/retro simultaneously
You’ll find a graduated scale located at the pivot point of the two slit lamp arms
It will give you the total separation between the two arms in degrees

27. Effect of angle (cornea)
45º: balance of surface and depth
5º: surface only
85º: depth only

28. This eye has iris naevi (freckles)
Wide beam/Diffuse
Used for general inspection of eye and adnexa
Good for colour assessment
Contact lens fit
Wide slit, diffusing inserted, microscope in front, illumination angle 30–50°, magnification of 6-10x
Patients are generally unable to tolerate the brightness of a wide beam
This eye has iris naevi (freckles)

29. Parallelepiped Default method for corneal inspection
Shows 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.

30. Optical section Allows judgement of thickness or depth
Use 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.

31. Indirect illumination
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.
Microscope
Lamp

32. Indirect illumination
Good for subtle detail, which would be obscured or washed out by large amounts of illumination
Light internally reflected within the cornea, or reflected by other surrounding tissue
Opacities 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

33. Indirectly illuminated
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

35. Retro-illumination Microscope Lamp
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.
Microscope
Lamp

36. Retro-illumination Light may be reflected from 2 main structures:
Iris: this back-lights the cornea
Fundus: this back-lights the lens
Opacities will appear dark against a bright background
For iris retro-illumination, use a narrow-moderate width slit, a wide angle of illumination, and magnification appropriate to the object size/extent
Decoupling 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

37. Indirectly illuminated
Retro-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).

38. 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.

39. Marginal retro-illumination
At 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)

40. Vacuole

41. Recommended reading Elliott, 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