Direct and MIO - Week 1 Flashcards
Compare Direct and MIO for the following:
- Image of Fundus (IOF)
- Image orientation (IO)
- Stereopsis
- Field of View (FOV)
- Magnification
- Limitation
Direct. MIO IOF: Virtual Real IO: Upright. Upright Stereo: No. No FOV: 5deg(2DD). 12deg(4DD) Mag: 15x. 5x Lim: Equator. Beyond Equator
What are the different clinical uses for an opthalmoscope?
- visualisation and localisation of opacities
- examination of vitreous and posterior pole
- examination of mid-peripheral retina
- assessment of fixation
- corneal or conjunctival defect/lesion (cobalt blue filter)
- PD + pupils testing
- Oreos Make Very Filling Cake Pastry
- opacities, mid-periph, ret., fixation, conjunctival, pupils
What aperture size do we generally use in preclin (for opthalmoscopy)?
The middle aperture
What aperture size is used for pupils/PD? (Dilated)
Large aperture
What aperture size is used for viewing the macula with opthalmascope?
Small aperture
What 3 controls do all modern opthalmoscopes have?
- On/off switch – also controls brightness of light. is usually found on the top of the handle
- Focus - adjusted by lens wheel (found on size of head of instrument, has a range of lens powers)
- Aperture of the light – for keeler it’s that switch on the back (for Heine it’s a dial on the front - because its precision german engineered and the superior ophthalmoscope)
How do you adjust focus for opthalmoscope?
- adjusted by lens wheel on the side
Dialing clockwise: Increases the lens power
Dialing counter-clockwise: Decreases the lens power - note: clockwise means downwards if opthalmoscope is upright
Adjusting lens power will move the focal point
What influences your choice of aperture?
What you are looking at
The pupil size
The region you are looking at
What’s the purpose of the slit beam?
- it highlights contours/indicates depth
- it is a source of indirect illumination
Why are glasses best removed from the px during ophthalmoscopy? Are there any cases where it’s better to leave them on?
- glasses often produce reflections and artifacts, and can be physically awkward during the examination
However, if they have a high Rx, it may be better to leave them on – b/c the ophthalmic lenses alone may not be powerful enough to neutralise a high refractive error
When looking through an ophthalmascope, which eye should we use?
Right eye for px right eye
Left eye for px left eye
What is the “red reflex” that you see when looking at a px’s eyes through an ophthalmoscope?
It is the reflection of the ophthalmocope light off the choroidal vessels
True or False: Viewing the red reflex is useful for determining the clarity of the ocular media?
True
What happens to the red reflex if there is a very dense opacity?
The red reflex disappears
What’s the primary first goal when looking through an opthalmoscope to a px’s eye?
To find the optic disc – use it as a reference point
What makes a Red-free filter?
A monochromatic green source light
Advantages of a Red-free filter?
- Increased vessel detail – red free light gives a better contrast b/w retinal vessels and the underlying background; easier to see vessels
- Easier to see nerve fibre layer (visualisation of NFL)
- Differentiate pigment/naevus from blood
- localisation of pigmentary lesions
Why is visualisation of the NFL (nerve fibre layer) important?
NFL loss could indicate gluacoma or optic nerve disease –> shown via the loss of the usual “stripey” look to the NFL
What happens to choroidal naevus, retinal naevus and blood when using red-free filter?
Choroidal naevus: disappears
Retinal naevus: stays the same
Blood: looks darker (than pigment)
(note: a naevus is basically just a pigmentation
How does refractive error of px influence the size of the fundus image in ophthalmoscopy?
Myopic patient: image appears slightly larger
Hyperopic patient: image appears slightly smaller
What are the potential problems that can occur with direct ophthalmoscopy?
- Unable to focus fundus image
- Insufficient FOV
- Unable to visualise fundus
- Unable to visualise macula
- Excessive reflections
How can you resolve an uncorrected high rx? (for ophthalmoscopy problem)
- use auxillary lenses
- view through patients rx (even though you’ll get increased reflections and decreased FOV it may still be worth it)
How to resolve uncorrected astig for ophthalm?
- view through rx
What could cause difficulty focusing fundus image?
- High refractive error
- Uncorrected Astig
- Media opacity
How to resolve media opacity?
- tilt ophthalmoscope to view around opacities
- dilate
How to resolve insufficient FOV (ophthalm)?
- move closer to px
- hold ophthalmoscope closer to eye
- semicircle aperture?
How to resolve unable to visualise fundus?
- check alignment
- hold px’s lids
- dilate
How to resolve unable to visualise macula?
- direct px to look to top edge of light
- change aperture/light intensity
How to resolve excessive reflections?
- check alignment/tilt ophthalmoscope
- direct px fixation: not straight into light
Why would you want to adjust the brightness of your ophthalmoscope?
You may want to reduce brightness to:
- reduce/minimise pupil constriction
- minimise px pain
Benefit of small aperture? (Medium actually because they call our small “micro”)
Provides easy view of the fundus through an undilated pupil. start with this aperture
Purpose of cobalt blue filter
(used in conjunction with fluorescein dye)
- is helpful in detecting corneal abrasions and foreign bodies
When performing opthalmoscopy (direct or MIO), where should the examiner be positioned?
15 degrees temporal side of patient
i.e. 15 deg temporal to the visual axis of the patient. Patient will be looking straight ahead
How can you obtain the largest view using MIO?
Compress the eyecup halfway against the patient’s brow
- (this allows the user to view the entire optic disc + many surrounding vessels at one time)
To examine the extreme periphery (MIO), instruct the patient to do what?
- look up to examine superior retina
- look down to examine inferior retina
- look temporally to examine temporal retina
- look nasally to examine nasal retina
What are the benefits of MIO?
- more peripheral view is possible (in undilated pupils)
- less dependent on px’s refractive error
- greater distance b/w px and optom (comfort)
- uncooperative children
- fundus screening
- px intolerant of bright BIO illumination
- monocular examiner unable to appreciate advantages of BIO
What is considered the technique of choice for looking at fundus? Why?
BIO - b/c it allows depth perception (3d images)
What is a normal cup disc ratio (C/D)?
0.30 or 0.35 (0.35)
What is a normal Artery to Vein ratio (diameter) (A/V)?
2:3
What colour is the normal fundus/posterior pole? What may be visible?
- red/yellow (pinkish tinge)
- temporal half may appear paler
- cupping may appear whitish
- lamina cribroa may be visible
What rule does the normal fundus follow?
ISNT rule I>S>N>T (in terms of size of neuroretinal rim) I = inferior region/border S = superior N = nasal T = temporal
What is the normal fundus elevation?
flat with slight central cupping (cup less than 0.5 of vertical diameter)
What is the normal fundus border?
distinct, possibly with surrounding pigment or pale crescent
What do veins look like compared to arteries in fundus examination?
veins are darker shade of red compared to arteries
What is AV nicking (arteriovenous nicking)?
Is the phenomenon where, on examination of the eye, a small artery (arteriole) is seen crossing a small vein (venule), which results in the compression of the vein with bulging on either side of the crossing.
– this is most commonly seen in eye disease caused by high blood pressure (hypertensive retinopathy)
What are the arteriovenous crossings like in a normal fundus?
- no compression at all
- no deviation
- no banking
Is spontaneous venous pulsation seen in fundus? Where?
spontaneous venous pulsation is commonly seen (up to 80%) as you exit the optic nerve head
What pattern does the normal Retinal Nerve Fibre Layer (RNFL) follow?
Bright, Dark, Bright
What does the normal macula look like in fundus exam?
macula apears darker than surrounding retina
