D - Ocular Imaging - Week 3 Flashcards

1
Q

Are dilating drops required for digital photography?

A

Not required. It has non-mydriatic capacity

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2
Q

What does fundus illumination with red/infrared light observe?

A

Deep layers (choroid): good for early detection of choroidal features (e.g. CNVM - choroidal neovascular membrane)

(longer wavelengths penetrate tissue more)

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3
Q

What does fundus illumination with blue/green light observe?

A

Superficial layers: good for NFL/RGCs/Vitreous

(shorter wavelengths penetrate tissue less)

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4
Q

What is the usual field size for digital photography? How can we increase FOV and to what degree?

A

20-45 degrees.

FOV can be increased with a mosaic (multiple fields aligned by software) to 75-90 degrees. (90-100 deg cover with 90-kowa/9 points of fixation)

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5
Q

What is the FOV for a Wide Field platform?

A

180 deg. Extends to vortex vein

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6
Q

What is the FOV for an Ultra-widefield (UWF) platform?

A

180 deg. Extends anterior to vortex vein

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7
Q

What is the FOV for a scanning laser ophthalmoscope (sLO)?

A

Can cover 200 degrees in a single sweep

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8
Q

Define luminescence

A

The emission of energy via the return of an electron from a high energy state to a lower energy state

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9
Q

What is the difference between fluorescence and phosphorescence?

A

Fluorescence = short term luminescence (<10^-6 sec-ms)
Phosphorescence = long term luminescence (>mins-hours)

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10
Q

How does auto-fluorescence differ from regular fluorescence?

A

the eye tissue itself is fluorescing, not a dye

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11
Q

What is Lipofuscin? At what wavelength does lipofuscin auto-fluoresce?

A

Undigested residue of cell membranes produced in lens and by dysfunctional RPE

Auto-fluoresces @ 488nm (blue)

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12
Q

When does lipofuscin usually accumulate? (2)

A

with age (cataract) and disease (diabetes)

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13
Q

At what wavelength does melanin auto-fluoresce? What does melanin loss (dark zones) indicate?

A

787nm (Infrared). Melanin loss indicates RPE stress/death

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14
Q

What can we use to detect RPE changes in lipofuscin? What about melanin?

A

Lipofuscin: FAF - Fundus AutoFluorescence
Melanin: NIA - Near infra-red autofluorescence

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15
Q

What do the dark areas in FAF indicate?

A

RPE dropout

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16
Q

How does fluorescein angiography work?

A

An injected contrast medium (typically NaFl) binds to proteins in blood (esp. albumin) and is retained in BV by Blood-Barriers (BB)

17
Q

Describe the appearance of fluorescein angiography in a normal patient

A

vascular tree will be visualised

18
Q

Describe the appearance of fluorescein angiography in a diseased patient with disrupted blood barrier

A

Medium will leak into the tissue to become lodged (pooling) where it normally is NOT found

19
Q

List and describe 3 methods to measure blood flow

A

Angiography: defines vascular routes + their integrity
OCT angiography (OCTa): no contrast medium, sequence of OCT images captures flow over time
Flowmetry: direct measure of rate + volume of flow

20
Q

How long does the injected medium in angiography take to appear in the eye?

A

8-15 seconds

21
Q

What are the 2 contrast media used for the eye in angiography? What do they each bind and which one is better at studying choroidal vessels or new vessel growth?

A

NaFl: binds plasma proteins + Hb
ICG (Indocyanine green): binds plasma proteins

ICG is good to study choroidal vessels or new vessel growth

22
Q

At what wavelengths are NaFl and ICG luminescent?

A

NaFl @465nm (525 emission)
ICG @ 805 (835 emission)

23
Q

What does ICG require?

A

infra-red film and special lenses

24
Q

How do you administer IV NaFl dye for angiography? (4)

A

Inject 5ml into antecubital vein
Take photos from 1 sec (red-free)
For 10-30 sec @ 2 sec (early)
Then 1, 3, 5, 10 mins (late)

(NB: ICG is same as above)

25
Q

Can IV administration of NaFl and ICG induce anaphylaxis? What about oral admin?

A

yes. Oral admin can’t though (but is limited to late stages)

26
Q

How do you administer oral NaFl or ICG dye for angiography? (3)

A

1gm/30Kg (max 6gm) as capsules mixed with sweetener
Warn patient to remove dentures + not spill
Photos @ 15, 30, 45, 60 (90 if needed) minutes

27
Q

What form of admin for NaFl/ICG has the most adverse effects? Name them

A

IV (2-5%): skin, urine, tissue coloration (NaFl only), nausea, dizziness, local skin allergy, phlebitis, skin necrosis, rarely anaphylactic death

28
Q

What type of administration for NaFl/ICG for angiography is preferred in children/younger patients?

A

Oral

29
Q

List the 5 Fluorescein Angiography phases (re time taken to get to see it) [WILL BE ON EXAM]

A
  1. Choroidal: @ <10sec
  2. Arterial: @ 10-12 sec
  3. Capillary (arterio-venous): @ 13-15 sec
  4. Venous: @ 16-20 sec
  5. Late (collagen stains): @ >30 sec
30
Q

Which phases of flourescein angiography are shown with oral administration of NaFl/ICG?

A

Only the late phase (phase 5). (which is a dull glow in A and V, with collagen stains @ disc edge)

31
Q

During which phase of fluorescein angiography can the foveal avascular zone be measured?

A

Capillary phase (phase 3)

32
Q

What can hypofluorescence be caused by? (2)

A

Masking (pigment, blood, hard drusen, haem, fluid, etc.)
Filling defects (vascular compromise, vasc. occlusion, capillary dropout, etc.)

33
Q

What can hyperfluorescence be caused by? (4)

A

Window defects (e.g. pigment loss allows choroid to be seen)
Vascular abnormalities (conformation, structure)
Leakage (from blood vessels or RPE)
Staining (late stage; absorption)