Slit Lamp Biomicroscopy Techniques- Anterior Flashcards
First before you start the techniques what must you do
Clean down equipment and ensure px is set up correctly so adjust chin rest and chair height so eye level with black marking
Turn room lights on to maximise contrast
Ensure px is comfortable and head is pressed up against the bar
Diffuse illumination
What can we see with it
What filter do we use and why
Overall view of anterior eye and adnexa.
Filter= diffuser which allows us to see the eye over an even illumination, if no diffuser then increase slit width till max but decrease brightness to avoid blinding the px
How do we carry out diffuse
Ask px to close their eyes so we can view their eyelids and lashes and check for pre orbital swelling
Reopen eyes check for blepharitis
View overall abnormalities on the surface of the cornea
Ask px to look in diff directions and gazes to check all areas of bulbar conjunctiva
Evert eyelids to check roughness of tarsal plate
What is diffuse used for
What structures can be observed
Overview of anterior eye, gross pathology, media opacities, vascularisation, lid swelling, ophthalmic photography
Cl fittings and aftercare
Used to detect quality of tear film/ unwanted debris (used w fluorescein and cobalt blue to check cls)
Useful for assessing lens positions, checking if there is adequate movement, detecting lens defects, determining surface quality and also wettability of lenses.
Lids, lashes, iris, cornea, conjunctiva, pupils
How do we carry out direct focal illumination- microscope and slit beam
Microscope is directly focused on the slit beam so illumination and observation system are focused at the same point.
How do we carry out dfi and what is it used for
The more anterior the structure..
Used to
Narrow down slit beam and height and increase illumination and mag, used for a more in depth exam after diffuse to spot and detect abnormalities.
The more anterior the structure the wider the angle needs to be between the observation and illumination system
Observed areas normally use cobalt blue filter and fluorescein
Used for anterior eye, obstructions, tear film assessments, soft contact lens fittings to see if a fit is too steep or too flat, used to detect surface deposits on lenses and even whether or not lenses are maintaining proper hydration.
Parallelpiped how do we do it and what does it study
How does the stroma appear compared to tear film and endothelium
Combination of a wide beam for surface study and narrow one for sections. Uses 1-2mm slit so narrow but not too narrow. Allows the corneal surface and stroma to be studied. We get some info about the surface and some ab the depth.
Slit beam can be modified using the dial, again make sure make px look gazes to check all areas of bulbar conjunctiva and fornices. Evert px eyelids again to check roughness of tarsal plate. 3 sweeps across cornea to scans or abnormalities.
For stroma it appears grey and the tear film is the brightest and endothelial zone looks brighter than the stroma
What is parallelpiped used for
Structures what structures does it assess
Used to see corneal nerves, endothelium folds, examine corneal structure and alterations, corneal scarring, infiltrates, corneal staining (fluorescein and blue filter) corneal abrasions, foreign bodies, surface and depth, stroma, contact lens stuff
Fitting of cls, tear film, nafl can be used w parallelpiped to evaluate how lenses interact w corneal tear film, fitting
3d view of cornea, crystalline lens, stroma, endothelium, epithelium, conjunctiva
Optic section describe beam and slit stuff
Why wont upper and lower parts of the beam be in focus and how can we combat this
Narrowest beam, upper and lower parts of the beam wont be in focus due to the curvature of the cornea so decrease slit height till all of the corneal section is equally in focus
Increase mag and brightness bc we have a thin slit
Slit width may need to be adjusted to maintain clarity
We can make the section look thinner or thicker by adjusting the angle between the illumination and observation system
Wide angle 60 degrees for depth estimation
How do we carry out optic section
Can try and move the whole section to the temporal part of the cornea and by doing this more of the corneal layers will become visible as the cornea is thicker in this layer and more differentiated- by focusing accurately and increasing mag we can see the different layers of the cornea
Tear film is the most anterior and hence the brightest, epithelium looks darker, bowman’s is bright and stroma appears grey and can be better observed with parallelpiped, endothelial zone can be seen as brighter than the stroma but not as bright as the tear film so bright thin band
We will get corneal reflections off iris= artefacts
Move angle between observation and illumination system to look from one side to another
What is optic section used for
And structures
Used to assess the depth of an opacity or anomaly once detected w parallelpiped, w high powers you can see nerve fibres and infiltrates, assess depth of lesions foreign body depth and depth of opacities in the cornea, can detect anterior hyalosis by using optic section to observe the anterior vitreous, provides a corneal layer by layer examination, localises corneal alterations, location of scar tissue, blood vessels, assesses media opacities
Can also detect if an area of staining is excavated, raised or flat. Can estimate anterior chamber depth eg van herricks method
Contact lenses- tear film and meniscus, Tyndall effect, can evaluate the tear layer under a permeable lens and aid in the fitting process
3d view of cornea, anterior chamber, crystalline or IOL lens, general view of anterior eye, obstructions, tear film assessments, endothelium, epithelium, stroma, vitreous
Conical
Third type of dfi
Here beam height and width is decreased, narrow vertical parallelpiped beam that forms a circular or square spot
Used to assess flare, cells, pigments in anterior chamber, aqueous flare- Tyndall effect, indicates active uveitis. Examines anterior chamber for debris, haze from aqueous chamber
Vitreous, anterior chamber, aqueous chamber
Sclerotic scatter theory behind it
Takes advantage of total internal reflection of light within the cornea, light entering cornea from side normally reflects within cornea and exits around the limbus creating a glow around the edge of the cornea.
Light breaks out of the cornea when it hits an irregularity eg swelling or foreign body in which case it appears as a haze near to the central cornea.
How to carry out sclerotic scatter
With room lights low to maximise contrast, focus light on the centre of the cornea
Lock slit lamp in in place so the observation system is focused on the central cornea, then decouple slit lamp and it should be aimed at the limbus where the conjunctiva meets the cornea (slit hits edge of cornea)
Light emitted around edges of the cornea as a circular glow but microscope remains focused on central coernea and opacities in that area lead to light scatter which will be seen against the dark background of the pupil.
So slit is focused on peripheral part of the cornea near to the limbus and light from it totally internally reflects in order to achieve the halo, abnormalities will lead to light scatter which can be seen from the central part of the cornea
What is sclerotic scatter used to assess
Detect unusual foreign bodies, infiltrates, corneal oedema, corneal abrasions, opacities
Theory behind specular reflection
Specular is when it is reflecting off a smooth surface
Angle of incidence= angle of reflection. Reflections only occur if this is achieved.
Quality of the reflection reflects the quality of the reflecting surface. So purkinje image is good
This can happen by change when scanning w optic sec or parallelpiped but can also be set up
How to carry out specular reflection
With room lights down and starting with a mag of x16 focus narrow parallelpiped slit beam on area of cornea to be examined, rotate observation system so it is 45 degrees to one side and check the cornea is still in focus. Now the light source needs to be rotated in the opposite direction by an equal amount so 45 degrees the other way.
Now a bright reflection should be visible= purkinje image
Bright reflection is from the tear film or epithelium and to the left of this is a smaller dimmer reflection which is aligned with the back surface of the cornea so the endothelium. And specular reflection of the endothelium is only seen down one eyepiece
Move joystick small amounts to bring the endothelium in focus to check if it is regular or irregular related to long term contact lens wear. Or look at the bright purkinje image if we want to assess the quality of the tear film.
Little bit more info on specular reflection - slit
To increase reflection what do we do to observation and illumination system
Once section is moved onto the purkinje image epithelial and endothelial cells both glow and ignore bright epithelial cells
Focus on dim, reduce height of section so that specific area is examined and increase the width of the slit to examine more of the endothelial surface
To increase reflection make sure the observation and illumination system are perpendicular to one another
Uses for specular reflection
What can it do for tear film particles
Mainly tear film, epithelium and endothelium
Subtle changes on surface texture of conjunctiva, tear film and tear cornea or contact lens, endothelial polymegahtism, contact lens wettability, pre corneal tear film
With specular reflection we can see lipid tear film particles moving in front of the corneal surface with every blink of the px so you can study tear meniscus and Tbut can be tested as we need to examine lipid tear film particles.
How does retro illumination work
How can we reduce glare and improve visibility
Illuminates the area from behind the structure so the cornea is retro illuminated by the iris or the retina. So it uses light from a more posterior surface to illuminate the observed areas.
Shine the illumination system through the cornea and majority of the light passes through and strikes the iris and scatters off the iris before illuminating the cornea from behind.
If there are any blood vessels or structures in the cornea they are illuminated from behind and would be visible in the light we see as a retro beam
To reduce glare and improve visibility, we can reduce the height of the slit and increase the mag to allow us to see vessels in greater detail
What is retro illumination used for
Useful to look at structures w low contrast on the cornea eg corneal nerves and blood vessels. Useful to view structures that would have otherwise been bleached by dfi.
Used for- neovascular growth, limbal or corneal vascularisation, dystrophies, keratoconus, crystalline lens assessment changes, cataracts, corneal changes, transillumination of iris, corneal oedema, opacities in crystalline lens so useful for cataract formation, corneal nerves, lid margins, keratoconus precipitates in the corneal endothelium, lens assessments (water clefts and vacuoles and anterior lens posterior subcapsular cataract etc)
Contact lens fittings- detect lens surface deposits, can view deposits within descemets membrane, fitting of contact lenses, lens surface deposits as it illuminates them from behind helping to determine shape and depth
Cornea, crystalline lens, iris, cornea, limbus
Indirect illumination
Light scatters from directly illuminated section into adjacent tissue where it provides a secondary field of examination
Practitioner views the structure to the side of the directly focused section, slit lamp should be decoupled to view the area under examination
Used for
Corneal examination, opacities, dystrophies, cl examination, vascularisation, limbal changes, corneal oedema, foreign bodies, limbal neovacularisation, corneal dystrophies, contact lens complications, vascularisation, limbic deficiency etc
Cornea, lid margins, conjunctiva, corneal limbus
