Ocular: Anatomy Principles Flashcards
What is Fundus autofluorescence?
-non-invasive imaging modality that can map natural and pathological fluorophores in the posterior pole
Does FAF require injection?
Nope
How is FAF obtained? ( instrument)
A confocal laser scanning opthalmoscopy or modified fundus camera
What does FAF use to create the image?
Uses fluorescent properties of lipofuscin within the RPE to create an image
What is lipofuscin?
A byproduct of the breakdown of photoreceptor outer segments
What is Blue light wavelength in FAF is absorbed?
470nm
What wavelength of yellow-green light is emitted from FAF?
600nm
What do the brighter area represent in the FAF image?
An increased lipofuscin density
What leads to RPE dysfunction/accumulation of lipofuscin?
Retinal pathologies
What do the blood vessels look like in a normal FAF?
-blood vessel appear dark (bc blood they absorb blue or green light completely)
**important!
Why does the optic nerve appear dark in FAF?
Absence of RPE or lipofuscin
How is fovea seen in normal FAF? Why?
-a spot of hypo-autofluorescence due to high concentration of xanthophyll pigment in the area
Areas of excess lipofuscin accumulation appear _______________
Hyperfluorescence (RPE dead/absent = hypofluorescence)
What is seen in abnormal FAF?
-increased levels of lipofuscin lead to regions of hyper-autofluoresence
What in the eye can cause regions of hyper-autofluoresence?
-presence of sub-retinal material
-optic discs drusen
-loss of macular pigment
-photoreceptor attenuation
Areas of increased levels of lipofuscin lead to areas of _______________
Hyper-autofluorescence
What in the eye can casue hypo-autofluoresence?
-RPE atrophy/tears
-acute intraretinal/subretinal tears
-fibrosis/scar tissue
-media opacities
When can geographical atrophy be seen?
Late stage dry and wet AMD
What is geographical atrophy?
Atrophy of the outer retinal tissue, RPE and/or choriocapillaris
Limitations to FAF:
-less signal strength than fluorescein angiography
-susceptible to artifact from media opacities
-limits clear visualization of central retina due to macular pigment absorbing blue light
What is fluorescein angiography(FA)?
An invasive diagnostic procedure that helps assess the anatomy, phys, and pathology of retinal and choroidal circulation
When was FA invented?
1961
What does FA require (equipment wise)?
-fundus camera w excitation and barrier filters
-fluorescein dye injected intravenously
Process of FA:
White light form camera flash passes through blue filter and then absorbed by unbound fluorescein molecules —> molecules then fluoresce
What color are blood vessels in FA?
Bright white, they are hyper-pigmented
Procedure for FA:
-intravenous injection (antecubital vein)
-injection speed must be sufficient for high contrast images
Light process for FA:
White light from a flash filtered through excitation filter (blue filter)
How is the image captured in FA?
-barrier filter captures only the emitted light from excited dye
-image taken immediately after injection and continues up to ten minutes
What are the purposes of FA?
-eval of vascular integrity of retinal and choroidal vessels
-integrity of blood retina barrier
What dyes can be used in angiography?
-sodium fluorescein
-indocyanine green
What is NaFl made from?
Organic vegetable dye
Wavelength ranges for excitation and fluorescence?
-excitation: 465-490nm
-fluoresces: 520-530nm
Where does the NaFl NOT diffuse?
outer and inner blood retinal barrier
Where DOES NaFl diffuse?
Choriocapillaris and Bruch’s membrane
How long does it take for NaFl to be eliminated by liver/kidney?
Within 24 hours
What color is the excitation filter and what spectrum does it absorb?
Cobalt blue, 465-490nm
What is the mechanism of the blue excitation filter in FA?
-blue flash excites unbound fluorescein molecules within vessels or leaked out
What color will be emitted from the structures containing fluorescein?
Green-yellow light
What is the mechanism of the barrier filter in the FA?
allows green-yellow fluorescent light through but keeps the blue reflected light out
Absolute contraindictions to FA:
-known allergy to iodine containing compounds
-H/O adverse reaction to FFA in past
Relative contraindications to FA?
-renal/hepatic failure
-asthma
-hay fever
-cardiac disease
-seizures(bc camera flash)
-pregnancy (esp 1st trimester)
Phases of FA:
- Choroidal phase
- Arterial phase
- Arteriovenous phase
- Venous phase
- Recirculation
Choroidal phase:
-10-15 seconds to reach retina after injection
-to retina via SPCA and LPCA -> choroidal filling seen first
Arterial phase:
-1-2 sec after choroidal phase
Arteriovenous phase:
-1-2 sec after arterial phase
-pre capillary arterioles, capillaries and post capillary venules
Venous phase phases:
Early, mid, and late phase
Early phase of venous phase:
Laminar flow
Mid phase of venous phase:
Complete venous filling
Late venous phase:
Reduced dye concentration in arterioles
Recirculation phase:
Dye concentrations reducing in vessels and complete emptying in 10 mins
Staining of what structures can be seen in Recirculation phase?
-optic disc
-bruch’s membrane
-choroid
-sclera
When is hypofluorescence seen in FA? Is it normal?
-secondary to blocking effect or because of vascular filling defect
-NOT normal
What arteries can cause vascular filling defects?
Retinal or choroidal vascular occlusions or SPCAs supplying optic nerve
Is hyperfluorescence in FA normal?
NOT normal (more fluorescence than normal expected)
What causes fluorescein leakage?
-leaky, incompetent blood vessels in neovascularization
-retinal vasculitis
-tumors, disc edema
What casues staining in FA?
-drusen and fibrosis
What causes pooling in FA?
Pigmented epithelial detachment
