Slit Lamp Flashcards
What is a slit lamp?
A narrow slit beam of very bright light produced by a tungsten or halogen lamp is focused onto the eye which is then viewed under magnification with a microscope
How do we see through the eye?
1) With diffuse light (wide beam) you have a general, frontal view of the eye - gives an overview of the cornea, iris and lens
2) With a narrow beam you can see a sagittal section through the thickness of a structure - gives the individual layers of cornea, lens
Slit Lamp Features
Illumination system Viewing system Magnification Coupling and de coupling Filters
Viewing System
- Focusing rings - two for stereo viewing - binocular image
- Converge toward image plane
- Important to set focus correctly before you use the slit lamp
- Adjust each eyepiece independently
- Adjust separation
Magnification
Change to obtain a more or less magnified view of the structure you are viewing
Coupling and De Coupling
Coupling = Light is focused at the same point to where the observation system is set De-coupling = Light is focused at a different ppoint to where the observation system is set
Filters
Diffusing filter - provides illumination that is not focused
Yellow filter
Blue filter - used when we place dye in the eye
Green filter - maximises contrast of red regions and allows you to see subtle blood vessels
Specialised applications of the slit lamp
- Tonometry (checking IOP)
- Assessment of anterior chamber depth
- Fundus examination (with additional lens) - steroscopic view using auxillary lens
- Assesment of fit of contact lenses
How can you use slit lamp for contact lens fit/after care?
- Assessment of contact lens surface, fit of soft and rigid cls
- Observe contact lens induced anatomical changes
What can you examine doing an external eye examination using SL?
- Eyelids
- Conjunctiva
- Anterior segment of the eye
How to conduct general examination of the anterior eye?
1)Set up SL
-use focusing rod or px eyelid to focus the light
-focus eyepieces monocularly
-set eyepiece separation
- ensure light beam is in centre of your FOV
*make sure instrument is coupled
2) Explain procedure
3) Hygeine - clean head and chin rest
4) Get px in position
-adjust chair height and/or chin height - px outer canthus level with mark on SL
5) Make sure px is comfortable
6) Room lights off
7) Fixating suitable target
Use one hand to control the lamp height and distance, and the other to control the slit beam, filters and magnification
What happens to corneal reflection depending on where the light is coming from?
- If light comes from left, the corneal reflection looks like a C
- Of light comes from right, the reflection looks like an inverted C
How does the positioning of the SL change what you can see?
- A wide angle bet the viewing and illumination system allows you to examine more superficial structures
- As you narrow the angle, you can examine deeper structures
- Moving SL in (towards px) or out allows you to look at deeper or more superficial parts of the anterior eye
What is direct illumination?
Observer looks exactly at the structures illuminated by the focused beam
What is indirect illumination?
Observer looks at the structures outside the illuminated area
-This may involve decoupling: break linkage bet viewing and illumination system
What are the direct illumination techniques?
Diffuse, Parallelepiped, Corneal Optic Section, Crystalline Lens Optic Section
What are the uses and settings of diffuse?
Uses: General examination of the external eye to observe the eyelids, lashes, conjunctiva, sclera and iris
Settings: Width of the beam is set to maximum, observation systerm is set perpendicular to px face ie light is directed straight ahead
- illumination system set at 45 degrees to that
- Mag is kept low 6-16x
-diffusing filter is placed in the light path
What are the uses and settings of parallelepiped?
Uses: scanning the cornea
Settings:
-Beam width is set to 2-4mm
-OS is set perpendicular to the px face
-IS is set 45 degrees to OS
-Low mag selectected, 6-16x
-Joystick brought forward until cornea in sharp focus
- Cornea scanned by moving beam from temporal to nasal side and when temporal cornea is viewed, IS should be directed from the temporal aspect etc
- Procedure repeated for inferior cornea with px looking up and superior cornea with px looking down and superior lid held high
What are the uses and settings of corneal optic section?
Use: determination of depth of opacity in cornea
Settings:
-Narrow beam 0.5-1mm wide
-OS set perpendicular to px face
-IS set 45 degrees to that
- Low mag initially 6-16x
- Focus beam on cornea, once its in sharp focus increase mark so you can see white line marking epithelium, the central granular stroma and a 2nd white line showing endothelium.
-As px blinks debris can be seen in tears in front of epithelium
What are the indirect illumination techniques?
Sclerotic scatter, and Van Hericks technique
What are the uses and settings of Sclerotic scatter?
Uses: detection of corneal oedema and irregularities such as corneal opacities
Settings:
-Parallelepiped beam placed at 45-60 degrees so that it illuminates either nasal or temporal limbus in a darkened room and is then viewed with the naked eye
Bright glow seen around limbus as light internally reflected bet epithelium and endothelium of cornea and then scattered by opaque sclera. Any disruption in regularity of cornea will be seen as grey hazy area
What are the uses and settings of Van Herick’s Technique?
Uses: Estimation of anterior chamber depth. This technique allows you to assess how much space there is bet the corneal endothelium and the anterior iris surface
Settings:
-1-2mm wide slit beam
-16x mag
-OS is placed perpendicular to the px face
-IS at 60 degrees to OS
-slit of light initially paced on sclera either temporally or nasally and then moved laterally towards the cornea until the beam just splits into 2, one beam reflected from cornea and one from the iris
- a dark region is seen between these reflections representing the anterior chamber
-thickness of anterior chamber compared to corneal section
What are the uses and settings of Crystalline Lens Optic Section?
Uses: Determine depth of opacity in crystalline lens
Settings:
-0.5-1mm wide beam
-OS set perpendicular to px face
-IS set about 30 degrees to that
-Low mag initially 6-16 x
-once youve achieved a corneal optic section, reduce mag and narrow angle bet OS and IS, but OS is still perpendicular to face
-move joystick a little in towards px until anterior lens surface is in focus and then increase mag to max
-now possible to see diff bands within lens
-to view nucleus and posteror pole, move joystick further in, passsing bulk of lens
What is the alternative setting for Sclerotic Scatter?
- Uncouple OS and IS
- OS still perp to px face, focus OS on cornea and lock into position
- Now move IS so light is directed to the limbus (a point location other than that at which OS is focused)
