FLUORESCEIN ANGIOGRAPHY

AND INDOCYANINE GREEN

ANGIOGRAPHY

• PRESENTER – Dr. KRATI GUPTA

• MODERATOR – Dr. RONEL SOIBAM

FLUORESCEIN ANGIOGRAPHY

• The study and diagnosis of retinal, macular and choroidal pathologic

lesions have been greatly revolutionized with the advent of fundus

fluorescein angiography (FFA).

• From an initial laboratory tool, it has now become a useful

diagnostic tool that has aided the diagnosis and monitoring of the treatment

of retinal vascular and macular diseases.

• Although the retina can be readily examined by direct and indirect

ophthalmoscopy and slit-lamp bio microscopy, the fluorescein angiography

provides a valuable addition to these techniques.

HISTORY OF FFA

• The technique of using intravenous fluorescein to evaluate the ocular

circulation was introduced 40 years ago by Mac Lean and Maumenee.

• Chao and Flocks provided the earliest description of fluorescein

angiography in 1958.

• Finally, it was introduced into clinical use in 1961 by Novotny and Alvis,

who demonstrated the photographic documentation of the fluorescein

dynamics.

• Over the last 3 decades advances have occurred in this sphere, digital

imaging has made possible the generation of high resolution angiography

of the retina and choroid.

INTRODUCTION

• Luminescence:

Emission of light from any source other than

high temperature.

• Fluorescence:

Luminescence that is maintained only by

continuous excitation. Property of certain

molecules to emit light energy of longer

wavelength when stimulated by a shorter

wavelength.

• Phosphorescence:

Luminescence where the emission continues

long after the excitation has stopped.

OUTER AND INNER RETINAL BLOOD

BARRIER

OUTER BLOOD–RETINAL BARRIER.

The major choroidal vessels areimpermeable to both bound and freefluorescein.

The walls of the choriocapillaris containfenestrations through which unboundmolecules escape into the extravascularspace.

It crosses Bruch membrane but onreaching the RPE are blocked byintercellular complexes termed tightjunctions or zonula occludens.

INNER BLOOD–RETINAL BARRIER

It composed principally of the tight

junctions between retinal capillary

endothelial cells.

Across which neither bound nor free

fluorescein can pass.

The basement membrane and pericytes

play only a minor role in this regard.

Disruption of the blood–retinal barrier

permits leakage of both bound and free

fluorescein into the extravascular space.

PRINCIPLE OF FFA

• Based on

Luminescence

Fluorescence

Phosphorescence

• Two filters are used:

COBALT BLUE EXCITATION FILTER

YELLOW GREEN BARRIER FILTER

.

EXCITATION FILTER

The dye absorbs light in the blue range of the visible spectrum with absorption peaking at 465 to 490 nm. The blue flash excites the unbound fluorescein within the blood vessels or the leaked out fluorescein.

The blue filter shields out all other light and allows through only the blue excitation light.

Structures containing fluorescein within the eye emit green-yellow light.

The blue light is reflected off of the fundus structures that do not have fluorescein.

BARRIER FILTER

The flourescein dye emits light from 500 to 600 nm with a maximum

intensity at 520 to 530 nm (green-yellow).

The blue reflected light and green-yellow fluorescent light are directed back

toward the film of the fundus camera.

Just in front of the film a filter is placed that allows the green-yellow

fluorescent light through but keeps out the blue reflected light.

Thus, even though the excitation and emission spectra are quite close, as long

as suitably matched excitation and barrier filters are used, only substances

capable of fluorescence are detected.

EXCITATION AND EMISSION SPECTRUM

OF FLUORESCEIN

SODIUM FLUORESCEIN

Sodium fluorescein (C20H10O5Na2)

Orange red crystalline hydrocarbon.

Low molecular weight (376.27 Daltons).

Nontoxic, inexpensive, safe, alkaline solution.

Fluoresces at Blood pH (7.37-7.45).

Absorbs blue light (480-500 nm).

Emits yellow-green (500-600 nm) (Peak 525 nm).

80% bound to plasma protein and also with

RBC.

Can’t pass through tight retinal barriers so allows

study of retinal circulation

CLEARANCE

• Complete removal from blood by kidneys and liver in 24-36 hrs.

Metabolism

• Sodium Fluorescein is metabolised to fluorescein glucuronide.

• 60% of fluorescein is present in the form of metabolites 30 minutes after injection, and 80% is metabolized after 60 minutes. 96% of the active substance is glucuronized after five hours.

Elimination

• The plasma half-life of fluorescein is 11 minutes. Elimination is predominantly via the kidneys, but also via the liver and in the faeces. Renal clearance is 1.75 ml/minute/kg bodyweight. A dose of fluorescein is excreted almost completely within 36 hours of administration.

DOSASGE AND ADMINISTRATION

Solutions containing 500 mg

of fluorescein are available

in vials of:

10 ml of 5% fluorescein

5 ml of 10% fluorescein

3 ml of 20% fluorescein

solution (750 mg)

For children, the dose is

calculated on the basis of

35mg for each 5kg. of

body weight.

Dye is injected as a bolus

into the vein of the

patient's arm.

• With a greater volume the injection time increases, with a smaller volume,

more fluorescein remains in the dead space between the arm and the heart.

• Therefore, 5 ml of 10% solution (500 mg) fluorescein is generally preferred.

• The venous dead space between the hand or the antecubital vein and the

heart may be 5 to 10 ml, leading to sluggish or reduced flow of fluorescein

into the central circulation.

• The fluorescein can be flushed with 5 to 10 ml of normal saline.

• An alternative is to elevate the patient’s arm above the level of the heart

using an adjustable armrest, reducing the fluorescein transit time to the heart.

CONTRAINDICATIONS

ABSOLUTE

1) Known allergy to iodine containing compounds.

2) H/O adverse reaction to FFA in the past.

RELATIVE

1) Asthma

2) Hay fever

3) Renal failure

4) Hepatic failure

5) Cardiac disease – cardiac failure, Myocardial infarction

6) Previous mild reaction to dye.

7) Tonic-clonic seizures

6) Pregnancy ( especially 1st trimester)

USE IN PREGNANCY AND LACTATION

• Controversial

• Avoid angiography on patients who are pregnant, especially those in first

trimester.

• Fluorescein Crosses the placenta

• Fluorescein is secreted in milk.

• Has been done in pregnancy with no adverse effect

• There have been no reports of fetal complications for fluorescein injection

during pregnancy.

INTERACTIONS

• Combination with beta-blockers may in rare cases cause lethal anaphylactic

reactions.

• Therefore, particularly in at-risk patients undergoing beta-blocker therapy

for whom fluorescein angiography is essential- the procedure must be

carried out under medical supervision, and with access to the necessary

resuscitation equipment during the whole examination.

• It should be born in mind that if such patients require resuscitation

measures, they may not respond fully to the use of adrenaline.

• The patient should be monitored for at least 30 minutes after completion of

fluorescein angiography.

COMPLICATIONS

MILD MODERATE SEVERE

Staining of skin, sclera

and mucous membrane

Nausea and vomiting

(10%)

Respiratory- laryngeal

edema, bronchospasm

Stained secretion

Tear, saliva

Vasovagal response

(1%)

Circulatory shock, MI,

cardiac arrest (<0.01%)

Vision tinged with

yellow

Urtricaria (<1%) Generalized convulsion

Orange-yellow urine fainting Skin necrosis

Skin flushing, tingling

lips pruritis

periphlebitis Extravasation of dye and

local tissue necrosis

EMERGENCY TRAY FOR FFA

An emergency tray including such

items as:

• 0.1% epinephrine for

intravenous or intramuscular

use;

• an antihistaminic,

• soluble steroid,

• aminophylline for IV use;

• oxygen should always be

available in the event of

possible reaction to fluorescein

injection.

TECHNIQUE AND EQUIPMENTS

The materials needed for fluorescein angiography are as follows:

1. Fundus camera and auxiliary equipment

2. 23 gauge scalp vein needle

3. 5 ml syringe

4. Fluorescein solution

5. 20 gauge 1 ½ inch needle to draw the dye

6. Armrest for fluorescein injection

7. Tourniquet

8. Alcohol

9. Bandage

10. Standard emergency equipment

EQUIPMENT

• The traditional fluorescein angiography unit has two 35 mm cameras, one

for color fundus photography while the other (black & white) for

fluorescein angiography.

• Most fundus cameras take 30° photographs (magnification of 2.5X on a 35

mm film), which are adequate for a detailed study of posterior pole lesions

especially macular diseases.

• Many camera units provide variable magnification at 20, 30 and 50

degrees.

• The 50° view is most useful for lesions involving a large area of the

fundus.

PROCEDURE

• Informed consent – explain the

procedure to the patient.

• Dilate patient’s pupil.

• Fluorescein solution, scalp vein

needle, 5 ml syringe and the

emergency tray is prepared.

• Check fundus camera for any fault.

• Observe lens and fundus camera for

any dust or opacity

• Feed the machine with patient

information – Name, MRD no, age,

sex, clinical diagnosis etc.

• The patient is positioned and the camera aligned.

• Color photography of both eyes.

• Red free photograph of the posterior pole is taken.

• Insert the scalp-vein needle, preferably at anticubital vein and inject the fluorescein dye 3ml of 20% solution in 5-10 seconds.

• Simultaneously inject fluorescein dye and start Fluorescein mode in machine.

• Once machine is set at Fluorescein mode timer will start and exciter and barrier filter will be activated.

• Oral administration at a dose of 30 mg/kg is an alternative if venous access

cannot be obtained or is refused; a 5 ml vial of 10% (100 mg/ml) sodium

fluorescein contains 500 mg, and pictures should be taken over 20–60

minutes following ingestion.

• Images are taken at 1–2 second intervals initially to capture the critical early

transit phases, beginning 5–10 seconds after injection, tapering frequency

through subsequent phases.

• Start fluorescein photograph 8 seconds after start of injection in young and

after 10 seconds in older patients

• Images may be captured as late as 10–20 minutes.

• When photography is done, reassure the patient that all went well and

remind him or her that the urine will be discolored for a day or so (24-36

hours). Make patient wait an additional 20 minutes for observation for

possible reactions to fluorescein.

SEQUENCE OF PHOTOGRAPHS DURING

FFA

• Color photograph of Each eye.

• Red free photograph of each eye

• Room light to be kept dim

• Activate Barrier and exciter filter , change the flash intensity and take control photographs.

• Once dye is being injected set the machine at fluorescein mode and start the timer.

FFA PROVIDES THREE MAIN

INFORMATION:

1. The flow characteristics in the blood vessels as the dye reaches and

circulates through the retina and choroid .

2. It records fine details of the pigment epithelium and retinal circulation

that may not otherwise be visible

3. Give a clear picture of the retinal vessels and assessment of

their functional integrity

FLUORESCEIN PATHWAY

• Arm-to-retina circulation time is 8-10

sec.

• Normally 10-15 seconds elapse between

dye injection and arrival of dye in the

short ciliary arteries.

• Choroidal circulation precedes retinal

circulation by 1 second.

• Transit of dye through the retinal

circulation takes approximately 15 to 20

seconds.

ANGIOGRAPHIC PHASES

Precise details of the choroidal circulation

are typically not discernible, mainly

because of rapid leakage of free

fluorescein from the choriocapillaris.

Melanin in the RPE cells also

blocks choroidal fluorescence.

The angiogram consists of the following

overlapping phase:

1. Choroidal

2. Arterial

3. Arteriovenous

4. Venous

5. Late( recirculation) phase

6. The dark appearance of fovea.

CHOROIDAL PHASE

The choroidal (pre-arterial) phase

typically occurs 9–15 seconds after

dye injection .

It is longer in patients with poor

general circulation.

It is characterized by patchy lobular

filling of the choroid due to leakage

of free fluorescein from the

fenestrated choriocapillaris.

• A cilioretinal artery, if

present, will fill at this

time because it is derived

from the posterior ciliary

circulation.

ARTERIAL PHASE

• The arterial phase starts

about a second after the onset

of choroidal fluorescence, and

shows retinal arteriolar filling

and the continuation of

choroidal filling.

ARTERIOVENOUS PHASE

• The arteriovenous (capillary)

phase shows complete filling of

the arteries and capillaries with

early laminar flow in the veins

in which the dye appears to line

the venous wall leaving an axial

hypofluorescent strip.

This phenomenon (laminar

flow) reflects initial

drainage from posterior

pole capillaries filling the

venous margins, as well as

the small vessel velocity

profile, with faster plasma

flow adjacent to vessel

walls where cellular

concentration is lower.

VENOUS PHASE

• Laminar venous flow

progresses to complete filling,

with late venous phase

featuring reducing arterial

fluorescence.

• Maximal peri foveal capillary

filling is reached at around

20–25 seconds in patients

with normal cardiovascular

function, and the first pass of

fluorescein circulation is

generally completed by

approximately 30 seconds.

LATE PHASE

• The late (recirculation) phase demonstrates the effects of continuous recirculation, dilution and elimination of the dye.

• With each succeeding wave, the intensity of fluorescence becomes weaker although the disc shows staining.

• Fluorescein is absent from the retinal vasculature after about 10 minutes .

DARK APPEARANCE OF FOVEA

The dark appearance of the fovea is caused by three factors:

Absence of blood vessels in the FAZ.

Blockage of background choroidal fluorescence due to the high density of

xanthophyll at the fovea.

Blockage of background choroidal fluorescence by the RPE cells at the

fovea, which are larger and contain more melanin and lipofuscin than else

where in the retina.

PHASE TIME ( IN Secs)

Choroidal phase 10

Arterial 10-12

Arterio venous 13

Early venous 14-15

Mid venous 16-17

Late venous 18-20

Late ( elimination) 5 MINS

KEY TERMINOLOGY IN FFA

• Hyperfluorescence: An area of abnormally high fluorescence (due to

increased density of the dye molecule)

• Hypofluorescence: An area of abnormally poor fluorescence ( due to a

paucity of dye molecules or due to masking of the fluorescence)

CAUSES OF HYPERFLOURESCENCE

• AUTOFLUORESCENCE

Autofluorescent compounds absorb blue light and emit yellow–green light in a

similar fashion to fluorescein, but much more weakly.

Autofluorescent lesions classically include:

Optic nerve head drusen.

Drusens.

AUTOFLOURESCENCE

• PSEUDO-FLUORESCENCE

It refers to non-fluorescent reflected light visible prior to fluorescein injection;

this passes through the filters due to the overlap of wavelengths passing

through the excitation then the barrier filters. It is more evident when filters are

wearing out.

• INCREASED FLUORESCENCE

It may be caused by;

(a) Enhanced visualization of normal fluorescein density.

(b) An increase in fluorescein content of tissues.

WINDOW DEFECT

It is caused by atrophy or absence

of the RPE as in :

Atrophic age-related macular

degeneration.

A full-thickness macular hole.

RPE tears.

This results in unmasking of normal

background choroidal fluorescence,

characterized by very early

hyperfluorescence that increases in

intensity and then fades without

changing size or shape.

• POOLING

Pooling in an anatomical space occurs due to breakdown of the outer blood–

retinal barrier.

A type of hyperfluorescence in which the dye accumulates within a closed

space. (e.g. RPED)

• LEAKAGE

Leakage of dye is characterized by fairly early hyperfluorescence, increasing

with time in both area and intensity. It occurs as a result of breakdown of the

inner blood–retinal barrier due to:

Dysfunction or loss of existing vascular endothelial tight junctions as in

Diabetic retinopathy

Retinal vein occlusion

Cystoid macular oedema

Papilloedema.

Primary absence of vascular endothelial tight junctions as

CNV

Proliferative diabetic retinopathy

Tumours

Coats disease.

LEAKAGE

• STAINING

It is a late phenomenon consisting of

the prolonged retention of dye in

entities such as

Drusen,

Fibrous tissue,

Exposed sclera

Normal optic disc

It is seen in the later phases of the

angiogram, particularly after the dye

has left the choroidal and retinal

circulations.

HYPOFLOURESCENCE

Reduction or absence of fluorescence may be due to:

(a) Optical obstruction (masking or blockage) of normal fluorescein density

(b) Inadequate perfusion of tissue (filling defect).

• Masking of retinal fluorescence. Preretinal lesions such as blood will block all fluorescence

• Masking of background choroidal fluorescence allows persistence of fluorescence from superficial retinal vessels:

Deeper retinal lesions, e.g. intraretinal haemorrhages, dense exudates.

Subretinal or sub-RPE lesions, e.g. blood

Increased density of the RPE, e.g. congenital hypertrophy

Choroidal lesions, e.g. naevi.

BLOCKED FLUORESCENCE

CAPILLARY NON-PERFUSION

A type of hypofluorescence

that results from non-filling of

the retinal capillaries due to

the anatomical or functional

reasons.

• FILLING DEFECTS

They may result from:

Vascular occlusion, which may involve the retinal arteries, veins or

capillaries or the choroidal circulation.

Optic nerve head filling defects as in anterior ischaemic optic neuropathy.

Loss of the vascular bed as in myopic degeneration and choroideremia.

SYSTEMATIC APPROACH TO FLUORESCEIN

ANGIOGRAM ANALYSIS

A fluorescein angiogram should be interpreted methodically to optimize

diagnostic accuracy.

1. Note the clinical findings, patient’s age and gender, before assessing the

images.

2. Note whether images of right, left or both eyes have been taken.

3. Comment on any colour and red-free images and on any pre-injection

demonstration of pseudo- or autofluorescence.

4. Looking at the post-injection images, indicate whether the overall timing

of filling, especially arm-to-eye transit time, is normal.

SYSTEMATIC APPROACH TO FLUORESCEIN

ANGIOGRAM ANALYSIS

5. Briefly scan through the sequence of images in time order for each eye in

turn, concentrate on the eye with the greatest number of shots as this is

likely to be the one with greater concern. Look for any characteristic

major diagnostic features.

6. Go through the run for each eye in greater detail, provide a description of

any other findings using the methodical consideration of the causes of

hyper- and hypofluorescence set out above.

INDOCYANINE GREEN ANGIOGRAPHY

• Indocyanine green (ICG) angiography (ICGA) is fast emerging as a

popular and useful adjunct to the traditional fundus fluorescein

angiography (FFA) in the diagnosis of macular, choroidal and outer retinal

disorders.

• This technique was introduced in ophthalmology in 1973 by Flower and

Hochheimer.

• FDA approved the ophthalmic use of ICG dye in 1975.

• It remained largely unpopular owing mainly to technical difficulties. With

the advent of videoangiogram recordings and the recognition of its

potential in delineating occult choroidal neovascular membranes, the

clinical use of ICGA has increased tremendously .

PRINCIPLES OF ICG

ICG fluorescence is only 1/25th that of fluorescein.

So modern digital ICGA uses high-sensitivity videoangiographic imagecapture by means of an appropriately adapted camera.

Both the excitation (805 nm) and emission (835 nm) filters are set atinfrared wavelengths.

Alternatively, scanning laser ophthalmoscopy (SLO) systems provide highcontrast images, with less scattering of light and fast image acquisitionrates facilitating high quality ICG video.

The technique is similar to that of FA, but with an increased emphasis on the acquisition of later images (up to about 45 minutes) than with FA. A dose of 25–50 mg in 1–2 ml water for injection is used.

It also exhibits a phenomenon referred to as concentration quenching. After a period of increasing fluorescence with increasing serum concentration, that results in peak fluorescence, further increase in concentration, paradoxically leads to decreased fluorescence. This is thought to result from dimer formation.

INDOCYANINE GREEN

The indocyanine green (ICG) is a tricarbocyanine dye that comes packaged as a

sterile lyophilized powder and is supplied with an aqueous solvent.

Molecular weight :774.97

It contains less than 5% sodium iodide (in order to increase its solubility).

It has a pH of 5.5 to 6.5 in the dissolved state, has limited stability, and hence

must be used within 10 hours after reconstitution.

98% of the injected dye is bound to plasma proteins, with 80% being bound to

globulins, especially alpha- 1 lipoproteins.

CLEARANCE

The dye is secreted unchanged by the liver into the bile.

There is no renal excretion of the dye

It does not cross the placenta.

The dye also has a high affinity for vascular endothelium, and hence

persists in the large choroidal veins, long after injection.

ADVERSE EFFECTS

Nausea, vomiting are uncommon.

Anaphylaxis, approximately equal incidence to FA.

Serious reactions are exceptionally rare.

ICG contains iodide and so should not be given to patients allergic to

iodine or possibly shellfish.

iodine-free preparations such as infracyanine green are available.

CONTRAINDICATIONS

ICGA is relatively contraindicated in liver disease (excretion is hepatic)

In patients with a history of a severe reaction to any allergen.

moderate or severe asthma

significant cardiac disease.

Its safety in pregnancy has not been established.

TECHNIQUE AND DOSAGE

The technique is similar to that of FA.

There is an increased emphasis on the acquisition of later images (up

to about 45 minutes) than with FA

A dose of 25–50 mg in 1–2 ml water for injection is used.

PHASES OF ICGA

Early – up to 60 seconds post-injection

Early mid-phase – 1–3 minutes

Late mid-phase –3–15 minutes

Late phase – 15–45 minute

EARLY PHASE (UP TO 60 SECONDS

POST-INJECTION)

• showing prominent choroidal arteries and poor early perfusion of the

‘choroidal watershed’ zone adjacent to the disc.

EARLY MID-PHASE

(1–3 MINUTES)

• showing greater prominence of choroidal veins as well as retinal

vessels.

LATE MID-PHASE (3–15 MINUTES)

• showing fading of choroidal vessels but retinal vessels are still

visible; diffuse tissue staining is also present.

LATE PHASE (15–45 MINUTES)

• showing hypofluorescent choroidal vessels and gradual fading of

diffuse hyperfluorescence

HYPERFLOURESCENE

A window defect similar to those seen with FA.

Leakage from retinal or choroidal vessels the optic nerve head or the RPE

gives rise to tissue staining or to pooling.

Abnormal retinal or choroidal vessels with an anomalous morphology

exhibiting greater fluorescence than normal.

HYPOFLOURECENCE

Blockage (masking) of fluorescence.

Pigment and blood are self-evident causes, but fibrosis, infiltrate, exudate

and serous fluid also block fluorescence.

A particular phenomenon to note is that in contrast to its FA appearance, a

pigment epithelial detachment appears predominantly hypofluorescent on

ICGA.

Filling defect due to obstruction or loss of choroidal or retinal circulation.

INDICATIONS OF ICGA

Polypoidal choroidal vasculopathy (PCV): ICGA is far superior to FA for

the imaging of PCV.

Exudative age-related macular degeneration (AMD): Conventional FA

remains the primary method of assessment, but ICGA can be a useful

adjunct, particularly if PCV is suspected.

Chronic central serous chorioretinopathy often difficult to interpret areas

of leakage on FA. ICGA shows choroidal leakage and the presence of

dilated choroidal vessels.

Posterior uveitis. ICGA can provide useful information beyond that

available from FA in relation to diagnosis and the extent of disease

involvement.

Choroidal tumors may be imaged effectively but ICGA is inferior to

clinical assessment for diagnosis.

Breaks in Bruch membrane such as lacquer cracks and

angioid streaks are more effectively defined on ICGA than FA

If FA is contraindicated.

ADVANTAGES OF ICGA OVER FFA

FA is an excellent method of studying the retinal circulation, it is of limiteduse in delineating the choroidal vasculature, due to masking by the RPE.

In contrast, the near-infrared light utilized in indocyanine greenangiography (ICGA) penetrates ocular pigments such as melanin andxanthophyll, as well as exudate and thin layers of subretinal blood, makingthis technique eminently suitable.

ICGA can be used even when the ocular media are too hazy for FFA. Thisis due to the phenomenon of Rayleigh scatter .

ICG fluorescence can be imaged even in the presence of considerableblood, due to the phenomenon of Mie or forward scatter.

The peak absorption of ICG coincides with the emission spectrum of diode

laser, which allows the selective ablation of chorioretinal lesions using ICG

dye-enhanced laser photocoagulation wherein a target tissue containing

ICG is exposed to the diode laser beam.

Photophobic patients tolerate ICGA better than FFA.

ICGA accurately measures the size of an occult choroidal neovascular

membrane(CNVM).

LIMITATIONS OF ICGA

The choriocapillaris cannot be imaged separately with ICGA since theiraverage cross-sectional diameter (21 μm) is much smaller than that of theirfeeding and draining vessels, and hence the fluorescence of the formercannot be differentiated from that arising from the latter.

The phenomenon of Mie scatter also masks the unfilled retinal vessels thatcannot be visualized well in low speed angiography systems.

Bright areas do not necessarily signify dye leakage due to the phenomenonof additive fluorescence

ICGA is poorer than FFA in the imaging of classic CNVM since the earlyhyper fluorescence of the CNVM is overwhelmed by theintense background choroidal filling.

Although superior to FFA in the imaging of occult CNVM, ICGA mayunderestimate the size of the CNVM.

Fundus fluorescein angiography ICG angiography

For retinal circulation For choroidal circulation

Dye used – sodium fluorescein Dye used – indocyanin green

80% plasma protein bound and low

MW

98% plasma protein bound and high

MW

Light of visible spectrum used Infrared spectrum of light used

Blue green filters used Infrared filters used

More side effects Less side effects

RECENT ADVANCES IN INDOCYANINE

GREEN ANGIOGRAPHY

Wide-angle angiography: This is carried out by performing ICGA with the aid of

wide angle contact lenses, such as Volk SuperQuad and a traditional Topcon fundus

camera. This allows real-time imaging of a wide field of the choroidal circulation up

to 160 degrees of field of view.

Overlay technique: This technique allows lesion on one image to be traced on to

another color or red-free image.

Digital stereo imaging: Elevated lesions such as PEDs can be better imaged in this

way.

ICG as a photo sensitizer: It is considered to be a cheaper alternative to vertoporfin

in photodynamic therapy of neovascular AMD& other disorders .

Digital subtraction ICGA: It uses digital subtraction of sequentially acquired ICG

images along with pseudo color imaging. It shows occult CNVM in greater detail and

within a shorter time than conventional ICGA.

FUTURE APPLICATIONS OF

INDOCYANINE GREEN ANGIOGRAPHY

In the future, ICGA is expected to play a more important and wider role

especially in the management of macular disorders.

Identifying subclinical neovascular lesions in the other eye of patients with

AMD. There are several reports that mention that 10% of such eyes with no

clinical or fluorescein angiographic evidence of an exudative process

harbor plaques of neovascularization evident on ICGA.

ICG-guided feeder vessel photocoagulation: SLO high-speed ICGA can

adequately image the feeding vessels of the CNVM which are 0.5 to 3 mm

in length and are believed to lie in the Sattler’s layer of the choroid.

HEIDELBERG RETINAL

ANGIOGRAPH

• HRA2 a product of Heidelberg

Engineering GmbH, Germany.

• Preferred imaging device of retinal

specialist in research centers and

apex institutes.

• Unique feature is dynamic high

speed angiography and higher

resolution.

16 frames per second motion images

Also called as Confocal scanning laser ophthalmoscope

It is used in the following basic modes like

• Fluorescein angiography (FA mode) 488nm

• ICGA mode 790nm

• Red free reflection 488nm

• Infrared reflection 820n

SCHEMATIC STRUCTURE OF CSLO

SALIENT FEATURES OF HRA

• Spherical refractive error of –12 to +30D can be compensated by setting the control dial.

• In addition, internal myopic lens of –6 or –12D spherical correction can be set without using any external lenses.

• HRA2 field of view are 30, 20 and 15 degrees

• Simultaneous mode – e.g. both FA and ICG images of identical areas can be captured and stored.

• Composite mode – the software of HRA2 automatically evaluate the images and connects them to one another, creating large composite image ( 100 or 80 degrees) .

• Fixation mode – ensure the patient’s visual fixation is stable there are both internal and external fixation lights.

• Wide angle objective – width of field is broadened to 57 degrees for examining the peripheral fundus. Can be used in composite mode also.

• Automatic real time module (ART) – software detects and corrects for eye movements. Helpful in imaging autofluorescenes, cloudy media or high astigmatism.

• Examining the anterior segment – to perform iris angiography by setting optics control to +40D and adjust the distance between camera and eye to optimize the focus.

• Stereoscopic viewing – helpful in examining the 3 dimensional images.

• Components of analytical software – converted into other image modes. Biometric functions also available

ADVANTAGES

Higher resolution and contrast

Used in imaging FFA, ICG and autofluorescene

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