Slit Lamp And Extra Lecture 4 Theory Flashcards
What filters are there
Cobalt blue light- used with nafl fluoroscein and it excites it illuminating it a green colour, good to identify abnormalities within the corneal epithelium. Blue filter is also good at evaluating fit of gas permeable lenses.
Yellow filter- used to screen out excessive blue light used as well with nafl to make the green even more vibrant helping to detect subtle disruptions
Green filter- for viewing vascularisation of the cornea, vessels appear almost black under this light
Neutral density- if larger slit heights or widths are used then this decreases the brightness, useful when using volk to decrease light= to avoid blinding the px
Red free- enhances contrast between blood vessels and surrounding ocular structures
Diffuser- overall view of anterior eye and adnexa. Useful for photography. Allows you to see cornea under an even illumination
What is slit lamp biomicroscopy used for
Screening eye, fitting of contact lenses, managing posterior and anterior eye disorders, examines posterior and anterior segments of the eye, detects diagnoses and manages progression of ocular diseases.
What do the observation and illumination system have in common
And overall what does the slit lamp consist of
They have a common pivot point
Slit lamp combines a illumination system with a focusable beam and an observation system which is a high resolution microscope to look into.
How to focus the slit lamp
We need a focussed eyepiece. So push them apart and rotate each of them anti clockwise and then look through each one monocularly and place a focusing rod in the centre of the pivot point and rotate each one monocularly till the beam of light hitting the focusing rod becomes clear.
What is the pivot point
How does light shine onto the focusing rod
Where the observation and illumination system pivots
Flat part of focusing rod should be facing the examiner, turn on illumination system and the slit beam should go from the illumination system straight onto the rod.
Describe the eyepieces
2 eyepieces with varying magnification. These can be removed. They come in either 10x or 16x magnification.
What if there is no rod
And what is parallax
Then you can focus it using the parallax method.
Parallax is when objects are moving at a constant speed but appear to be moving a greater amount if they are closer to the observer than at a distance.
How to focus it using the parallax method
Rotate light from the illumination system left or right whilst using a flat background eg the bridge of someones nose, or a flat box on pxs head.
Eyepiece should be focused at the centre of rotation
To find this centre of rotation push the slit lamp back and fwds whilst rotating it left and right till achieve parallax movement= constant speed.
If you go too far in= with
Too far out=against
Where does illumination usually come from
And how can we achieve a sharp edge using what-
Illumination usually comes from above and reflects off a mirror into the eye. This creates an image for the observation system. Using a condensing lens creates an aerial image between the slit lamp and the examiner.
We can achieve a sharp edge by using a physical aperture and an optical system
What can we do to the slit lamp slit
The slit beam can be varied in height width angle and intensity by using the rheostat voltage dial
When you widen beam make sure to reduce illum of rheostat to avoid blinding the px
Describe the observation system
What does it have to change mag
Describe eyepieces and what can we do to them
Turret to modify the magnification. (6.3x, 10x, 16x, 25x, 40x)
Flipper for 1x/1.6x mag
Has various mag systems (biomicroscope has parallel eyepieces)
Eyepieces can be interchanged to increase mag to 10x or 16x
Reticle can be added to assess ocular structure, size and shape= Measurement device which needs to be calibrated
Describe the illumination system
It has a lever to change the slit height and this varies on diff instruments, some may be a dial
Lamp slit height and filters
Use it to monitor progression of pathology
Slit height can measure tear meniscus height
Endothelial polymegathism
What can practitioners do with these 2 systems
Practitioners can manipulate these 2 systems to achieve 6 main methods of slit lamp examination
BIO advantages
What can you see with BIO
Increased detail of fundus compared to direct
Stereoscopic view so can see disc cupping, raised lesions, retinal tears, sub retinal neovascular membrane, any feature w height or depth
Wide fov
Rx doesnt affect magnification
Media opacities dont affect mag so sharper image as image is formed anterior to the eye
Greater wds but this varies with power changing
BIO disadvantages
Px often needs dilating (mydriatic= tropicamide) or sympathomimetic (phenylephrine) which can cause blurred vision or photosensitivity. Note pre and post IOP measurement in case of acute glaucoma
V bright light so discomfort- no viewing over 40 seconds
Less portable
Requires additional lenses
Difficult to master
Expensive
Horizontal and vertical Diplopia- adjust headset for head mounted BIO
Describe where illumination comes form for posterior and with the volk lens
Illumination comes from above and bounces off the centre of the eye creating an aerial image between slit lamp and examiner. The condensing lens creates an inverted and laterally reversed image of the pxs fundus so need to move lens in opp directions.
Focus slit lamp using a parallel height type beam and focus on cornea and pull back till scratches on lens, pull back more and fundus should be in focus.
Different powers and mag and fov and wd
60D = 1.15x. Fov=67degrees. Wd=11
78D = 0.93x. 84. 8
90D. = 0.75x. 94. 6
Superfield NC= 0.76x. 95. 7
As power increases fov increases but wd decreases bc flatter curvatures focus light over a greater distance and magnification also decreases as fov increases so mag will decrease as you can see more but less detail. So 60 has the highest mag but 90 has the highest fov along with superfield. For retinal exams use 78 and 90 so you can have a wide fov to examine the peripheral areas.
Purple lenses
Held one way= 78D
Other way=90D
Hruby lenses what are they mag and vd
Have a power of 58D
Vd= 10-20mm
Type of condensing lens placed directly on the surface of the eye. Give virtual images as it focuses on the posterior lens at the nodal point. Used with slit lamps to examine the retina and optic nerve
Advantages of hruby lenses
High mag
Wide fov
Allows examiner to examine posterior segment in detail
disadvantages of hruby lenses
Poor px fixation
Poor glare tolerance
Affec by media opacities
Requires contact w eye may lead to temp blurring of vision
Topical anaesthetics may be required
Training needed
Hard to use on px w small eyes
What are steroids like prednisone linked to
Cataracts
Different uses of bio
Flashing lights floaters
Diabetic retinopathy
Tumours
Optic disc changes
Amd
High myopes= avoids gross magnification and decreased fov….
Traumatic head or eye injuries
Problems with BIO
Image is aerial and laterally reversed and inverted
Condensing lens needed to move in opp direcs than expected
Reflections from lens surface Need to be controlled
Hard to view fundus through undulated pupil
what are condensing lenses tinted and why
Tinted yellow to absorb blue wavelength light to decrease px discomfort and to protect the retina from photo toxicity I
Other indirect methods
Welch Allen monocular- panoptic/ keeler
Modified monocular
Scleral indentation
Used with slit lamp to get extreme peripheral views confirming holes or tears
Thimble and bar to press on the globe of the eye and you can see the ora serrated
Needs a dilated eye and training
Mirrored lenses
Lens has contact w the cornea, and this can be used to view posterior pole mid and far periophery
20D lens used with a direct ophthalmoscope
Used to examine retina
Mirrored surface help to reduce glare and increase visualisation
Helps to reflect light into the eye
Why is there a much sharper image obtained in the presence of media opacities
Due to the greater intensity of light source and bc the image is formed anterior to the eye.
What are the two types of dilating agents and what do we need to check
Both mydriatic dilating agents
Antimuscarinic- tropicamide 0.5/1 percent
Sympathomimetic- phenylephrine 2.5 percent
Make sure you check anterior chamber angle
Where can mirrored lenses look into
Posterior pole
Mid and far periphery
Optic disc changes
AMD
Diabetic retinopathy
Tumour
Optic disc changes- increased cupping w glaucoma, raised ONH with pappiloedema, disc drusen
Amd- greater fov allows easier visualisation of serous detachments of the neurosensory retina in exudative or wet AMD
Diabetic ret- larger fov gives overall picture, detection of macula oedema (raised)
Tumour- can help with differential diagnosis between flat benign naevus and raised malignant neoplasm
