Slit lamp II (techniques)

Question 1

What are the five direct illumination techniques?

Answer 1

Diffuse illumination, parallelepiped, optical section, specular reflection, and tyndall cone.

Question 2

What are the two indirect illumination techniques?

Answer 2

Retro-illumination (of iris or lens) and Sclerotic scatter

Question 3

Explain the technique: Diffuse illumination

Answer 3

• Whole eye is illuminated with the edge of the light beam being either diffused or outside the field of view
• Surface tissues are seen
• 3D shape is not easily seen but useful for photography
• Very little info about depth of structures inside the eye and almost no infoa bout the shape of the optical surfaces
• Allows overview - i.e. colour/redness
• Options: wide beam with diffuser or without a difuser

Question 4

Answer 4

Diffuse illumination used to see the surface of the eye. There’s a spot in the eye but we don’t know which structure exactly it is on (no depth info)

Question 5

Answer 5

Diffuse illumination to get an overview of the eye surface (redness/vascularisation).

Question 6

Explain the technique: Parallelepiped

Answer 6

• Beam: 0.5mm or wider
• Enables size and position information to be obtained
• Cornea is approx 0.5mm thick so the corneal section can be a true parallelepiped.
• Light must come from the side (30˚) to provide shape and depth information
• Edges of the beam are visible
• Surface of the tissues is less visible but the 3D shape of structures is seen easily and depths can be seen.

Question 7

Answer 7

Technique: Parallelepiped
- Illumination system on the left side (30˚).
- White rectangular part is the front of the cornea
- The dot on the rectangular part can be distinguished to tell that it’s on the cornea.
- The gap between the white (cornea) and orange (iris) is the anterior chamber
- Can also tell the thickness of the cornea (its shadow on the right side).
- Shape of the cornea and flatness of the iris surface can be seen, fine corneal anomalies can be seen against the dark pupil.

Question 8

Explain this technique: Optical section

Answer 8

• Very thin focused beam of light created “section” through transparent structures of the eye so that the structures of tissues in depth can easily be seen (provides best depth info).
• Shone from the side
• Can be used to look at the lens –> decrease the angle to view the posterior part of lens.

Question 9

Answer 9

Technique: Optical section

Question 10

Answer 10

Technique: Optical section

Question 11

Answer 11

Technique: Optical section

Question 12

Answer 12

Technique: Optical section

Question 13

Explain the technique: Specular reflection

Answer 13

• Allows the roughness of a surface to be seen
• Cell outlines on the corneal endothelium are visible
• Based on the property of a material
• By shining directional light at a surface, the unevenness of the surface can become visible if observing at the correct angle (i.e. light and observation system at the same angle but on opp sides).
• Specular reflection can be conducted on the corneal endothelium and anterior lens.

Question 14

Answer 14

Specular reflection - corneal endothelium
- Parallelepiped beam from one side, high mag to see surface irregularities (40x)
- Move around cornea until bright reflection (artefact) of the slit beam is seen in ONE eye piece.
Tune illumination (beam width) so that the anterior and posterior surface reflections don’t overlap.

Question 15

Answer 15

Specular reflection - anterior lens
- Moderate beam width from little to the side
- Focus on the lens surface near the edge of the iris
- Alter the angle of the microscope until a bright orange peel reflex becomes visible
- Adjust the magnification and beam width as necessary
- Focus accurately

Question 16

Explain this technique: Tyndall Cone

Answer 16

• Narrow short beam passes only through the optical media, allows for detection of colloidal fluids or debris.
• Tyndall effect: scattering of light as a beam passes through a medium containing either very fine particles or a colloid.
• Aqueous humour should ideally be optically empty (looks black), unless there are proteins and inflammatory cells (WBC).
• 2mmx2mm square beam OR tall thin bream within pupil coming across your line of sight from the side.
• Aim beam into the pupil and focus between the cornea and lens.
• Remove all the other light so only the tyndall cone beam remains.
• Observe how the light path is seen in the scatter from the aqueous, and how some of the scattering particles are visible.

Question 17

Answer 17

Technique: Tyndall cone

Question 18

Answer 18

Technique: Tyndall cone

Question 19

What is NaFl used for in tyndal cone?

Answer 19

NaFl (dye) can be placed in the anterior chamber to view the aqueous humour more easily. You would be able to spot the cells moving with the convention current in the A.C.

Question 20

What happens in indirect illumination?

Answer 20

Illumination and optical system do not move around a concentric point (px’s eye). Out of click stop/decoupled.
- Shine bright light on a part of the eye, from which you get diffuse scatter onto other parts of the eye (which is what you examine).

Question 21

What are the two indirect illumination techniques?

Answer 21

Retro-illumination and sclerotic scatter

Question 22

What happens in retro-illumination?

Answer 22

Light is directed onto a tissue deeper in the eye than the structure being examined. The reflected light will be the light source.

Question 23

In which two scenarios can you use retro-illumination?

Answer 23

1) Shining light on the retina (reflecting = source), to examine the lens
2) Shining light on the iris (reflecting = source), to examine the cornea.

Question 24

Why can it be difficult to examine the lens via retro-illumination (indirect)?

Answer 24

To view the lens via retro-illumination, you shine light through the pupil onto the retina, for it to reflect back onto the lens. However, this causes the pupil to constrict (react to light). Thus, dilation drops may be necessary.

Question 25

Answer 25

Technique: retro-illumination of the retina, to view the lens. You can see the cataract around the cortical region of the lens.

Question 26

Answer 26

Technique: retro-illumination of the iris (source), reflecting light back onto the cornea (examined).

Question 27

Which beam width do you use for indirect illumination?

Answer 27

Parallelepiped beam (0.5mm thick)

Question 28

Explain the technique: Sclerotic scatter

Answer 28

Indirect illumination technique; beam uncoupled from the microscope and shone on the sclera next to the limbus. The cornea is examined using light “piped” within the cornea.

The light bounces off back surface, across the cornea. Total internal reflection occurs, light transmits across the whole cornea

Question 29

Whats the difference between optic section and sclerotic scatter?

Answer 29

With optic section, we can see the depth of the cornea.
With sclerotic scatter, we can see the extent of the cornea.

Question 30

Answer 30

optic section –> sclerotic scatter

Question 31

What does red-free illumination look like?

Answer 31

As a light source, illuminating the eye
Green filter, removes the red wavelengths so that blood vessels and haemorrhages can appear more black.