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
