slit-lamp

Question 1

what is a slit-lamp?

Answer 1

a narrow slit beam of very bright light produced by a tungsten or halogen lamp is focused on to the eye which is viewed under magnification with a microscope

Question 2

what are the different ways we see the eye through the SL?

Answer 2

. with diffuse light ( wide beam ) you have a general frontal view of the eye so you can see overview of cornea , iris and lens

. with narrow beam you can see a sagittal section through the thickness of a structure
individual layers of cornea , lens

Question 3

what is sagittal plane ?

Answer 3

. sagittal plane - in relation to body is cross-section cut through from front to back from nose to back of head

. in relation to eye - section through from the front of eye to back of eye

Question 4

what are slit lamp features ?

Answer 4

. illumination system
. viewing system 
. magnification
. coupling and de-coupling
. filters

Question 5

what is the illumination system ?

Answer 5

. its the bit of slit-lamp that light comes out of
. you can swing illumination system from side to side to adjust the direction the illumination is coming from
. you can also adjust the width and the height of slit beam
. you can also adjust brightness

Question 6

what is the viewing system/observing system ?

Answer 6

. part of slit-lamp that you look through
. focusing rings - two for stereo viewing - binocular image
you can see the depth of what you’re looking at - stereoscopic view -
. two eye pieces converge towards image plane
. important to set focus correctly
. adjust each eye piece independently from each other
eye piece on LHS will adjust with right eye shut
eye piece on RHS will left eye shut
. adjust separation - move eye piece towards each other or further away from each other so they match up to your PD distance

Question 7

what is the magnification system ?

Answer 7

change to obtain a more or less magnified view of the structure you are viewing

Question 8

what is the slit lamp biomicroscope/joy stick ?

Answer 8

all slit-lamp have biomicroscope all you to move whole slit lamp system either forwards / backwards
left/right
up/down - by twisting joy stick

Question 9

what is the difference between coupled and de-coupled slit-lamp ?

Answer 9

. coupled - light is focussed at same point to where the observation system is set -
this means when looking through viewing system whatever your light is pointing at is in focus .

. de- coupled - light is focussed at a different point to where the observation system is set
in some cases where you want to focus on something that is on the side of where your illumination light is pointing
light will be pointing at one portion of the eye and the observation system will be pointing and focussed on a different part of the eye

Question 10

what are the different slit lamp filters which change the light that we see ?

Answer 10

. diffusing filter - provides illumination that is not focused - observation system is still focused , light scatters across eye instead of focused slit

. yellow filter - enhance contrast in image

. blue filter - enhances view of fluorescent dye when that’s inserted in the eye

. red - free- filter or green filter - maximises contrast of red region
enhances regions that might be red in the eye
you can see red-free filter to see blood vessels or bleeds in eye

Question 11

slit - lamp application ?

Answer 11

. examination of the external eye and anterior segment of the eye

. specialised application -

• tonometry - checking intraocular pressure
• assessment of anterior chamber depth
• fundus examination with additional lens
• assessment of fit of contact lenses

Question 12

what features of the external eye can you examine with the SL ?

Answer 12

. eyebrow
. eyelid 
. cornea 
. iris 
. sclera 
. conjunctiva 
. eyelashes

Question 13

how to setup slit lamp ?

Answer 13

. use focussing rod or patients eyelid to focus the light

. focus eyepiece monocularly

. set eyepiece separation

. ensure light beam is in centre of your field view

. ensure instrument is coupled

. explain procedure

. get patient in position - adjust chair height and chin height - px outer canthus( outer corner of eye ) is level with mark on slit-lamp

. room light is off
. tell patient where to look

. use one hand to control the lamp height and distance and the other to control the slit beam , filters and magnification

. if light comes from the left , the corneal reflection looks like a c
bar on right is reflection from iris which is further back in the eye

.if light comes from the right , the corneal reflection looks like an inverted c
bar on left is reflection from iris

Question 14

what does wide angle between the viewing system and illumination mean ?

Answer 14

. allows you to examine more superficial structures

Question 15

what does narrow angle between the viewing system and illumination mean ?

Answer 15

you can examine deeper structures

Question 16

what does moving slit lamp in or out mean ?

Answer 16

moving slit lamp in ( towards px ) or out ( away from px ) allows you to look at a deeper or more superficial parts of the anterior eye

Question 17

how to focus into deeper structure ?

Answer 17

. narrow the angle between viewing and illumination

. push slit lamp in toward px

Question 18

what is direct illumination ?

Answer 18

. whatever we are looking at through slit lamp is lit up by the beam of the slit lamp

. observer looks exactly at the structures illuminated by the focussed beam

Question 19

what is indirect illumination ?

Answer 19

. observer looks at the structure outside the illuminated area
. we might want to do this because the beam is so bright sometimes when we shine it directly into things it can bleach them so we can’t see

. this may involve decoupling ; break linkage between viewing and illumination system

Question 20

what is diffuse illumination technique ?

Answer 20

. form of direct illumination
. use : general examination of the external eye to observe the eyelids , lashes , conjunctiva , sclera and iris

. setting : beam width set to maximum , observation system set perpendicular to the px face ( light is directed straight ahead ) and illumination system set at about 45 degrees to that .
magnification low at 6 - 16 x
and diffusing filter is placed in the light path
can put thin tissue in front slit lamp mirror on the illumination system

Question 21

what is parallelepiped technique?

Answer 21

. direct illumination
. use - scan across various parts of eye ( cornea , iris , lens and conjunctiva )

. settings : the beam width 2 to 4 mm : observation system perpendicular to patients face and illumination at 54 deg to the observation , low magnification 6-16 x

. we start off with illumination on temporal side of patient and we scan across , when we get to half way across cornea we move illumination to 45 deg to patients nasal side and scan across

Question 22

what is the corneal optic section ?

Answer 22

. use : determination of depth of opacity in the cornea
allows you to see different layers of cornea
can examine depth of foreign body in the cornea

settings : narrow beam , 0.5 mm to 1mm wide , observation system perpendicular to px face and illumination system about 45 degree , low mag initially 6-16x

. if you want to focus corneal section on the temporal side of the cornea you will keep your illumination system on temporal side and if you want to focus on nasal side you will move your illumination system

Question 23

what is crystalline lens optic section technique ?

Answer 23

. direct : illumination
. use : determination of depth of opacity in crystalline lens
layered regions of the lens can be seen
. settings : narrow beam , 0.5mm to 1mm wide , observation system perpendicular to the patients face and illumination system about 30 deg , low mag 6-16 x

Question 24

what is sclerotic scatter technique ?

Answer 24

. indirect illumination
• Use: Detection of corneal oedema and irregularities such as corneal opacities or deposits.
works based on total internal reflection of cornea
• Settings: parallelepiped beam placed at 45 to 60 degrees so that it illuminates the either the nasal or temporal limbus ( where cornea meets the conjunctive ) in a darkened room and is then viewed with the naked eye.
• Bright glow seen around limbus as light internally reflected between epithelium and endothelium of cornea and then scattered by opaque sclera. Any disruption in regularity of cornea will be seen as grey hazy area

Question 25

what van Herick’s technique ?

Answer 25

• Use: Estimation of anterior chamber depth. This technique allows you to assess how much space there is between the corneal endothelium ( back of cornea ) and the anterior iris surface ( front of iris )
- if anterior chamber is small this means that there isn’t enough room to pass through drainage angle which can cause glaucoma
• Settings: 1-2mm wide slit-beam, 16 x magnification, the
observation system is placed perpendicular to the patient’s face and the illumination system at 60 degrees to this.

. place beam of light on cornea on temporal limbus of eye and keep cornea on focus
you will get white beam of light which is reflecting from cornea , you will get dull strip in the middle which gap between back of cornea and front of iris and brown strip behind that is strip from iris
. interested in how wide that dark space in the middle compared to how wide your white corneal beam is

Question 26

what do the gap cornea ratio’s mean in Van herick ?

Answer 26

.if gap ratio is 1:1 the width of dark gap is same as width of cornea this means that we have wide open angle and in von herick grading terms is called grade 4

.if gap ratio is 0.5:1 the width of dark gap is as half as wide as cornea the van herick grade is 3 still wide angle

if gap ratio is 0.25:1 the width of dark gap is quarter of width of corneal beam that is grade 2 and considered small angle - small anterior chamber depth

if gap ratio is <0.25:1 the width of dark gap is less than quarter of width corneal beam then it is grade 1 and considered dangerously narrow angle and risk of closing and can be sight threatening