Slit Lamp Flashcards
what do you do during preparation for a slit lamp examination?
- sanitise the lamp, dials, chin rests, head rest etc
- setup the patient correctly using the black markers on the sides
- quickly explain the procedure to your patient
how do you focus the slit lamp?
- first set beam to medium width and magnification to high, 16x
- find the NEUTRAL POSITION, where there is no sideways movement of the beam
- lock the slit lamp into place
- focus the eyepieces individually by turning anticlockwise all the way and then clockwise until target is in focus
- set pupillary distance correctly so you can see through both eyepieces at the same time
- whole thing should be done in a minute
what are some general pointers for slit lamp examinations?
- tell patient to look at your ear while examining, unless something else is required
- if light comes from the LEFT, corneal reflection looks like a ‘C’ if light comes from the RIGHT, corneal reflection looks like an INVERTED ‘C’
- WIDER VIEWING angle for more superficial structures, NARROWER VIEWING ANGLE to examine deeper structures in the eye
- speak out loud and explain what you are doing
- move SL in or out to see deeper or more superficial structures
what is DIRECT ILLUMINATION?
when the observer looks exactly at the structures illuminated by the focused beam
what is INDIRECT ILLUMINATION?
when the observer looks at the structures outside the illuminated area
direct illumination: diffuse
max beam width, turn brightness down slightly, observation system perpendicular to patient’s face, illumination system at 45 DEGREES to observation system, LOW MAGNIFICATION (6-16x) - DIFFUSING FILTER placed in the light path or a thin piece of tissue - pull the layers of a tissue apart so you have one thin layer and then place this over the diffuser
should see something that resembles a crater on an orange planet
direct illumination: parallelepiped
beam width 2 to 4mm, observation system perpendicular to patient’s face and illumination system at 45 DEGREES TO THE OBSERVATION SYSTEM, LOW MAGNIFICATION, 6 - 16x
scan across the eye and underneath the patient’s eyelids whilst doing this technique, keeping the structures of the patient’s eye in focus
need to switch the position of the illumination system as you scan across to MAINTAIN THE ‘C’ shape cornea reflection. As you go past the midline of the cornea swing the illumination system to the other side, once again at 45 DEGREES so that the ‘C’ shape is maintained
should see the clear ‘C’ shape and iris reflection scanning across the eye
direct illumination: corneal optic section
narrow beam, 0.5mm to 1mm wide, observation system perpendicular to patient’s face as usual, high brightness illumination system at 45 DEGREES TO THE OBSERVATION SYSTEM, LOW MAGNIFICATION INITIALLY 6 - 16x.
to see the different layers of the cornea more clearly you can make the beam height shorter or INCREASE MAGNIFICATION TO SEE THESE LAYERS IN MORE DETAIL
you should be able to make out the edges of the ‘C’ shape cornea reflection being brighter than the inside part, this is the layers
direct illumination: crystalline lens optic section
narrow beam, 0.5mm to 1mm wide, observation system perpendicular to patient’s face once again and illumination system makes angle of 30 DEGREES WITH OBSERVATION SYSTEM.
low magnification initially 6 - 16x, may have to move slit lamp closer to patient to see lens in focus
should see shiny lens at the centre of the eye and the layers inside, the reflections of the iris and cornea (orange and white) can still be seen but they shouldn’t be in focus, the lens should. So move the SL closer until the lens is focused and these are no longer in focus
indirect illumination: sclerotic scatter
parrallelepiped beam, 2-4mm wide, closer to 2 in reality, placed at 45 TO 60 DEGREES TO THE OBSERVATION SYSTEM, move the slit lamp so that the SLIT IS ILLUMINATING THE LIMBUS OF THE EYE
the limbus is just the perimeter of the clear cornea (coloured part of the eye), its the part where the sclera just begins to surround the cornea, so you can illuminate either the nasal or temporal limbus of the cornea - it doesnt matter.
should be done in a darkened room and seen with the naked eye, should see a bright glow around the limbus as light internally reflects like a glowing halo
indirect illumination: van herick’s technique
1-2mm wide slit beam, 16x magnification. Observation system perpendicular to patient’s face as standard and illumination system AT 60 DEGREES TO OBSERVATION SYSTEM
you need to try be very accurate with the 60 DEGREE ANGLE and BEAM or else you might not see this properly
should see the corneal section with the layers and a gap between the corneal section (white) and the reflection of the iris (orange)
we then grade van herick based on the ratio of the thickness of the gap and the thickness of the cornea
- grade 4 (open) - 1:1, the gap is the same width as the corneal section thicknes
- grade 3 (open) - 0.5:1, black space is half of the thickness of the cornea
- grade 2 (very narrow) - 0.25:1, black space is a quarter of cornea thickness
- grade 1 (dangerously narrow) - <0.25:1, black space is less than a quarter of the cornea thickness, this person has a high risk of developing CLOSED ANGLE GLAUCOMA
