slit lamp techniques Flashcards
what is tear break up time related to
the wetting properties of the tears and the rate of tear production
what is a normal tear break up time
> 10 seconds
list 4 types of people that TBUT is reduced in
- elderly
- xerophthalmia
- sjogrens syndrome
- CL wearers
what is instilled in the patient’s eye in order to assess TBUT
flourescein, wetted with saline
what must not be used to wet a flourescein paper strip and why
tap water, as this can cause pseudomonas
what must be checked on the saline before using it
its expiry date
which 2 filters on the slit lamp is used to assess the TBUT
- cobalt blue filter (for the flourescein)
- wratten filter (increases contrast)
list the method of observing TBUT
- focus on the cornea and observe the green tear film
- ask the patient to take a blink and then stare straight ahead
- count the number of seconds until you observe dark blue patches appearing on the green tear film
- when you see this, then stop counting
- this is your TBUT
what must you focus the slit lamp beam on when assessing TBUT
the cornea
when do you stop counting when assessing TBUT
when blue patches appear on the green tear film
as this is your TBUT
what is technique for observing the ‘orange peel’ called
specular reflection
what is structure is being observed with specular reflection (orange peel)
anterior surface of the crystalline lens/corneal endothelium
what magnification should be used with specular reflection
high x32-40
what slit beam width should be used with specular reflection
2mm paralellopiped
what is the illumination angle with specular reflection
angle on incidence = angle of reflection i=r
where is the slit beam focussed with sclerotic scatter
on the limbus
how is the light from the slit beam reflected with sclerotic scatter
the light is internally reflected within the cornea and re-emerges around the limbus
a halo of light is produced by total internal reflection
which two ways is the eye viewed, with sclerotic scatter
- can be viewed without the microscope
or - if the microscope is to be used, it must be decoupled from the illumination system
which magnification should be used with sclerotic scatter
low or naked eye
what slit beam width should be used with sclerotic scatter
2mm with parallelepiped
which type of viewing technique is sclerotic scatter
indirect
what is the illumination angle for sclerotic scatter
decoupled system
where should you focus the slit beam with sclerotic scatter
on the cornea
what two pathologies can be picked up with sclerotic scatter
- corneal opacity
- corneal oedema
what does sclerotic scatter check for in the eye
the corneal integrity
what are the three types of illumination used in slit lamp
- direct illumination
- indirect illumination
- retroillumination
how is direct illumination used
the observer looks directly at the structures illuminated by the focussed beam
list all the things which are viewed by direct illumination
- General view /Conjunctiva and fornices
- Lid margins /Lash follicles /Puncta
- General cornea /Tear film
- Limbal vessels
- Iris detail
- Lens section
- Anterior chamber
- Anterior chamber angle, van Herick
how is indirect illumination used
the observer looks to the side of the illumination
what technique uses indirect illumination
sclerotic scatter, to see the conceal integrity
how is retroillumination used
the observer uses light reflected from a more posterior source to view an object
what type of illumination is retroillumination a form of
indirect illumination
how is retro illumination used to view neovascularisation
the observer uses light reflected from the iris or the retina to view the neovascularisation
what is diffuse illumination good for
giving a good overview of the eye and lids and lashes
what 2 things in the lid margin should you look at with diffuse illumination
- punctum
- meibomian glands
what should the illumination angle be when using diffuse illumination
Swing illumination between 30 deg nasally and 30 deg temporally
list the 4 types of optic sections
- corneal section
- paralellopiped
- lens section
- van herick
what should be the illumination angle with a corneal section
wide of atlas 45 deg
what does a greater angle correspond to with a corneal section
greater angle = wider optical section
how is the corneal section seen as in the slit lamp
as a grey arc
what can be seen in the arc with a higher mag in corneal section
a narrow bright band can be seen on the outer (epithelium) and inner (endothelium) radii of the arc and the dark band between is the stroma
what is referred to as a parallelepiped
the view of a ‘slice’ of the cornea
how do you get a parallelepiped section of the cornea
- obtain a corneal section
- now widen the beam to 1-2mm
what is an optical section useful in determining
depth of an opacity in the cornea and for examining cataracts
what magnification should be used to viewing the lens section
low mag
how do you obtain a view of the lens in a lens section
first focus on the iris and then move across to the centre of the pupil
how will the crystalline lens be viewed in a lens section
a bright band at the front and back (anterior and posterior cortex) and several lighter bands in the centre, giving it a layered onion like appearance
why are you concerned about the angle of the anterior chamber
closed angle glaucoma
who might be at risk of a closed angle glaucoma
elderly and hyperopic patient
when can you induce a closed angle attack
when you dilate a patient
what is van herrick used for
to assess the depth of the anterior chamber
what mag should be used in van herrick and why
low 10x or 16x, to give adequate depth of focus
at what angle should the illumination system be to the microscope in van herrick
60 deg
where should you instruct the patient to look when carrying out van herrick
directly at the microscope
how do you obtain a view of the anterior chamber with van herrick
position a very narrow slit beam on the sclera and move across until you reach the limbus and the beam splits into two
what are you assessing the ratio between with van herrick
the ratio between the iris and the back surface of the cornea and the thickness of the cornea
what ratio of the gap and corneal thickness and grade is a angle which is wide open in van herrick
1:1 grade 4
what ratio of the gap and corneal thickness and grade is a angle which is open
0.5:1 grade 3
what ratio of gap and corneal thickness and grade is a angle which is suspicious
0.25:1 grade 2
what should also be done if an anterior chamber angle which is suspicious ~grade 2 is found in van herrick
gonioscopy
list 5 reasons that flourescein is used for
1) To detect lesions of the corneal epithelium
2) To examine the fit of RIGID contact lenses
3) In applanation tonometry
4) To evaluate the tears (Tear break up time TBUT)
5) To demonstrate the patency of lacrimal drainage
what is flourescein angiography and how is it carried out
This is a technique used by ophthalmologists to examine the integrity of the retinal vascular system.
It involves injecting 5ml of 10% fluorescein into the brachial vein and then viewing the fundus under UV light. Any leakage of the retinal vessels will be apparent
where does purkinje image 1 come from
the tear film
which purkinje image is the brightest
purkinje image 1
where does purkinje image 2 come from
corneal endothelium
which purkinje image is the hardest to see
purkinje image 2
where does purkinje image 3 come from
anterior surface of lens
it is the orange peel effect (i=r)
where does purkinje image 4 come from
back surface of the lens
