D - Ocular Imaging - Week 3

Question 1

Are dilating drops required for digital photography?

Answer 1

Not required. It has non-mydriatic capacity

Question 2

What does fundus illumination with red/infrared light observe?

Answer 2

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

(longer wavelengths penetrate tissue more)

Question 3

What does fundus illumination with blue/green light observe?

Answer 3

Superficial layers: good for NFL/RGCs/Vitreous

(shorter wavelengths penetrate tissue less)

Question 4

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

Answer 4

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)

Question 5

What is the FOV for a Wide Field platform?

Answer 5

180 deg. Extends to vortex vein

Question 6

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

Answer 6

180 deg. Extends anterior to vortex vein

Question 7

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

Answer 7

Can cover 200 degrees in a single sweep

Question 8

Define luminescence

Answer 8

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

Question 9

What is the difference between fluorescence and phosphorescence?

Answer 9

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

Question 10

How does auto-fluorescence differ from regular fluorescence?

Answer 10

the eye tissue itself is fluorescing, not a dye

Question 11

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

Answer 11

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

Auto-fluoresces @ 488nm (blue)

Question 12

When does lipofuscin usually accumulate? (2)

Answer 12

with age (cataract) and disease (diabetes)

Question 13

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

Answer 13

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

Question 14

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

Answer 14

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

Question 15

What do the dark areas in FAF indicate?

Answer 15

RPE dropout

Question 16

How does fluorescein angiography work?

Answer 16

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

Question 17

Describe the appearance of fluorescein angiography in a normal patient

Answer 17

vascular tree will be visualised

Question 18

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

Answer 18

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

Question 19

List and describe 3 methods to measure blood flow

Answer 19

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

Question 20

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

Answer 20

8-15 seconds

Question 21

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?

Answer 21

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

ICG is good to study choroidal vessels or new vessel growth

Question 22

At what wavelengths are NaFl and ICG luminescent?

Answer 22

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

Question 23

What does ICG require?

Answer 23

infra-red film and special lenses

Question 24

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

Answer 24

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)

Question 25

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

Answer 25

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

Question 26

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

Answer 26

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

Question 27

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

Answer 27

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

Question 28

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

Answer 28

Oral

Question 29

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

Answer 29

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

Question 30

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

Answer 30

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

Question 31

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

Answer 31

Capillary phase (phase 3)

Question 32

What can hypofluorescence be caused by? (2)

Answer 32

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

Question 33

What can hyperfluorescence be caused by? (4)

Answer 33

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)