DIS - Ocular Imaging I - Week 3 Flashcards
Does digital photography of the eye have non-mydriatic capacity or are dilating drops required?
Has non-mydriatic capacity
How large is the field of view typically in digital photography?
20-45 degrees
What are mosaics?
Multiple fields are aligned by software to get wide field imagery
What cans tereo separation (ie with a mirror) or serial photos give additional information on?
Depth information
Briefly define luminescence, fluorescence, and phosphorescence.
Luminescence is when electrons in a molecule absorb energy to move to a higher orbit, and then return, releasing a specific longer wavelength
Fluorescence is short term luminescence
Phosphorescence is long term luminescence
What is fundus autofluorescence?
Some eye components can produce brief luminescence with illumination
List two ocular compounds that autofluoresce and at what wavelength. For each, describe what one would expect to see with normal vs abnormal ocular health.
Lipofuscin at 490nm
-usually builds up with age and disease
Melanin at 790nm
-melanin loss (dark zones) indicates RPE stress/death
Where is lipofuscin produced (2)? What is it?
By the lens and dysfunctional RPE
It is undigested residue of cell membranes
What can be used to enhance RNFL definition?
Less red light makes the RPE darker and will improve contrast
Describe briefly how fluorescein angiography works.
Contrast medium binds to proteins in the blood, especially in blood vessels by the blood-brain barrier
Is contrast media needed with OCTa?
No
What is flowmetry?
Direct measure of rate of volume of flow
Describe the method for angiography.
Indroduce contrast medium into the bloodstream at the arm and monitor appearance in the eye ~15 seconds later
Pattern and time information can be derived
List two common contrast media for the eye and how they work. Note if they extravasate with leaky vessels.
Sodium fluorescein - binds to plasma proteins and haemoglobin - extravasates with leaky vessels
Indocyanine green - binds to plasma proteins - doesnt extravasate with leaky vessels, is very large
What is indocyanine green good to study (2) and what does it require (2)?
Choroidal vessels or new vessel growth
Requires infrared film and special lenses
Can injected contrast media induce anaphylaxis? What about oral?
Yes for injected
No for oral
List some common adverse effect sof contrast media.
Skin, urine, tissue discolouration
Nausea, dizziness, local skin allergy, phlebitis, skin necrosis, anaphylactic death
Are adverse effects common or rare with contrast media? Keeping this in mind, how does this alter its administration in children and younger patients?
They are rare but because death is a possibility, oral intake for OCT angiography is preferred in children and younger patients
List the fluorescence sequence for the eye following NaFl administration, including seconds (t minus) (5). What stage does oral give?
Choroidal - <10 seconds
Arterial - 10-12 seconds
Capillary - 13-15 seconds
Venous - 16-20 seconds
Late (collagen stains) - >30 seconds
Oral intake only gives the late stage
Can OCTa give similar resoltution to flurescein angiography?
Yes
List the two types of fluorescein anomalies give6 examples and what can cause them.
Hypofluorescence (dark)
-masking - pigment/blood
-filling defects - vascular defects
Hyperfluorescence (glow)
-window defects - pigment loss
-vascular abnormalities - conformation/structure
-leakage - from blood vessels/RPE
-staining - late stage absorption
Keeping the fluorescein anomalies in mind, what should always be taken alongside an angiogram to make sense of the anomalies?
A colour photo
List three pigments that can cause masking.
Xanthophil (macula)
Melanin
Choroidal naevus
List two lipofuscin/blood components that can cause masking.
Hard drusen
Haemorrhage
Can cell hyperplasia cause masking?
Yes
List two things that can cause filling defects.
Retinal/choroidal vascular occlusion
Capillary dropout
What is a filling defect?
When a blood vessel appears like it is not filled
A colour photo will reveal if this is the case or not
What is the mechanism behind a window defect? List two causes.
Lack of pigment
-albino
-past infection
