Fluorescein Angiography

Retina The retina composed of two parts : A. Neurosensory retina which composed of 9 layers 3) The internal limiting membrane 4)   The nerve fiber layer 5)   The ganglion cell layer 6)   The inner plexiform layer 7)   The inner nuclear layer 8)   The outer plexiform layer 9)   The outer nuclear layer 10)  The rod and cone inner and outer segments 11) The external limiting membrane B. Retinal pigment epithelium (RPE) : which composed from monolayer of cells & its functions are : • Absorption of scattered light. • Control of fluid and nutrients in the subretinal space (blood-retinal barrier function). • Visual pigment regeneration and synthesis. • Synthesis of growth factors to modulate adjacent structures. • Maintenance of retinal adhesion. • Phagocytosis and digestion of photoreceptor wastes. • Electrical homeostasis. • Regeneration and repair after injury or surgery. Blood supply :The retina receives its nutrition from two discrete circulatory systems—the retinal blood vessels and the uveal or

Basic facts

 Normal central retinal capillaries  Normal peripheral retinal capillaries  Plugged peripheral retinal capillaries

Optical phenomena

Transparency of neurosensory retina 1. Normal  Transparent structures 2. Decreased 1. Post mortem 2. Blood 3. Melanin

Optical phenomena

Transparency of retinal pigment epithelium 1. Normal 1. Melanin granules 2. Decreased 1. Macula 2. Hypertrophy of RPE 3. Choroidal folds 4. Choroidal nevi 3. Increased 1. Drusen 2. Scars, degenerative processes

Optical phenomena

Transparency of Bruch’s membrane 1. Normal 1. Elastic layer 2. Increased 1. Angioid streaks

Mechanical phenomena 1. Attachment of retinal pigment

epithelium 2. Normal 

Hemidesmosomes

3. Disturbed 

Pigment epithelial detachment

Fluorescein Angiography  Fluorescein angiography or fluorescent

angiography, is a technique for examining the circulation of the retina using the dye tracing method. Described in 1959 by MacLean and Maumenee

 Fluorescein binding: on entering the circulation,

between 80% of fluorescein molecules bind to serum proteins (mainly albumin). The rest remain unbound and are referred to as free fluorescein.  It provides three main information:  the flow characteristics in the blood vessels as the dye

reaches and circulates through the retina and choroid.  it records fine details of the pigment epithelium and retinal circulation that may not otherwise be visible.  give a clear picture of the retinal vessels and assessment of their functional integrity.

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Characteristics of fluorescein Nontoxic , inexpensive

and safe.

Sodium fluorescein

(C20H10O5Na2) is an organic dye. It is an alkaline solution and is highly fluorescent. Absorbs blue light, with

absorption peaking at 490nm (blue).

It emits yellow green

light at.

Effective at pH 7.37-7.45  It is metabolized by the

liver and excreted by the kidneys Most dye is cleared with 24 hours and kidneys and patients should be warned that their urine will appear orange during this time. 16

During pregnancy and lactation

•Controversial •Fl. Crosses the placenta •Has been done in pregnancy with no adverse effect •Do it when necessary

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Hazards Minimal relatively safe drug Use of dilating drops Red after – images from the photoflash Temporary tan skin color Fl. Urine discoloration Interfere with serological tests 2-4% Transient nausea and occ. VOMITING Hives, asthmatic symptoms Laryngeal edema Rarely – Syncope, anaphylactic rxn, MI, resp. or Cardiac arrest Rx – oral or I.V. Benadryl or Cortisone A physician in the 1st few minutes 18

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Anatomic and Physiologic Considerations Retinal B.V. , choricapillaris, large choroidal vessels Optic disc – normal fluorescent, no leakage Ciliary body leaks dye in A/C and vitreous

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Equipmen t Exciter filter: Allows only blue light to illuminate the retina. Depending on the specific filter, the excitation

wavelength hitting the retina will be between 465-490 nm. Most only allow light through at a wavelength of 490 nm. Barrier Filter: Allows only yellow-green light (from the fluorescence) to reach the camera. Both filters are interference filters, which means they block out all light except that at a specific wavelength. The barrier filter only allows light with a wavelength of 525 nm, but depending on the filter it can be anywhere from 520-530 nm. Fundus Camera with camera body containing black and white, or slide positive film. Also digital cameras tethered to computers have come into use since the late 1990s and are beginning to dominate the market today.

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How is fluorescein angiography performed?  5ml of 10% sodium fluorescein dye is injected as a bolus into

the vein (preferably antecubital) of the patient's arm.  The eye is illuminated using blue light produced by a blue filter (excitation filter).  The fundus is viewed through a yellow filter (barrier filter).  As blue light cannot pass through a yellow filter in normal circumstances nothing can be seen. However, fluorescein dye within retinal and choroidal blood vessels absorbs blue light and emits yellow light, this yellow light passes through the filter and is photographed. Only tissues that contains fluorescein are visualized .

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Normal circulatory filling # 0 seconds — injection of fluorescein # 9.5 sec — posterior ciliary arteries # 10 sec — choroidal flush # 10-12 sec — retinal arterial stage # 13 sec — capillary transition stage # 14-15 sec — early venous stage #16-17 sec — venous stage # 18-20 sec — late venous stage # 5 minutes — late staining Fluorescein enters the ocular circulation from the internal carotid artery via the ophthalmic artery. The ophthalmic artery supplies the choroid via the short posterior ciliary arteries and the retina via the central retinal artery, however, the route to the choroid is typically less circuitous than the route to the retina. This accounts for the short delay between the "choroidal flush" and retinal filling.

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Normal angiogram can be divided into five  phases: Choroidal

   

phase Arterial phase Capillary phase Venous phase Late phase

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Arterial phase

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Venous phase

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Venous phase

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Fluorescein angiography is used mainly for the study of abnormal ocular vasculature. The following are the main indications for fluorescein angiography

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Diabetic mellitus: 1. detecting any significant macular oedema which is not clinically obvious; 2. locating the area of oedema for laser treatment; 3. differentiating ischaemic from exudative diabetic maculoplathy; 4. differentiating between IRMA and new blood vessels if clinical differentiation is difficult.

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Retinal vein occlusion: 1. 2. 3. used 4.

determining the integrity of the foveal capillary bed and the extent of macular oedema following branch retinal vein occlusion differentiating collaterals from neovascularization less commonly it is purely to determine the extent of retinal ischaemia (as this can be done clinically) 36

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Age-related macular degeneration: 1. locate the subretinal neovascularization and determine its 2. suitability of treatment

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Other indications: 1. Locating subretinal neovascular membrane in various conditions (high myopia, angioid streaks, choroidal rupture and chorioretinitis) 2. Locating abnormal blood vessels (for example idiopathic retinal telangietasia, retinal retinopathy etc) . 3. Looking for break down of RPE tight junctions (central serous retinal retinopathy) or the blood retinal barrier (cystoid macular oedema) 4. Help with diagnosis of retinal conditions (for example Stargardt's disease gives a characteristic dark choroid). 37

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Interpretation of pathology of FFA

The following are common abnormalities seen in fluorescein angiography: •Timing •Abnormal dye distribution

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Pooling (in a space) Leak Staining (in a tissue).

Hyperfluorescence

Transmission increase

Pigment epithelial window defect Retinal

Abnormal vessels

Subretinal Tumors

Retinal Pooling

Sensory retina detachment

(in a space) Subretinal Hyperfluorescence

Cystoid edema

Leak Retinal Staining (in a tissue). Subretinal

Retinal pigment epithelium Noncystoid edema Perivascular staining Drusen Scars Sclera Lamina cribrosa

(A) Color and (B) red-free photgraphs of a fundus with soft drusen and hyperpigmentatio (C) Soft drusen hyperfluoresce during the early phase of angiography (D) stain in the late phase

cystoid macular oedema with petaloid pattern.

Pigment Hyperfluorescence

Transmission

Epithelial

Increase

Window Defect

Atrophy Drusen

Left macular hole. There is left foveal hyperfluorescence due to loss of the marking effect of RPE cells.

Retinal

Hyperfluorescence

Abnormal Vessels Subretinal

Tumors

Tortuosity and Dilation Neovascularization Microaneurysms Aneurysms Macroaneurysms Telangiectasias Shunts and collaterals Neovascularization Vessels in scar Angioma Retinal Retinoblastoma Hemangioma Subretinal Melanoma Metastases

Transmission Decrease (blocking effect) Hypofluorescence

Filling defect (delay and occlusion)

Transmissionc Hypofluorescence Decrease (blocked)

Pigment

Melanin Hemoglobin Xanthophyll Lipofuscin

Exudates

Hard Soft

Edema and transudate Other abnormal materials

Best`s disease Foreign body Fundus flavimaculatus

H y p o f l u o r e s c e n c e

Artery Retinal

Filling defect (delay and occlusion)

Vein Capillary bed

Dystrophies Loss of tissue

Subretinal

Degeneration Nonperfusion

Choroideremia Choroidal atrophy etc. Myopia Central areolar atrophy

Autofluorescence

Autofluorescence of optic nerve head drusen. A. Preinjection photograph of the optic nerve in a patient with optic nerve head drusen. Both barrier and exciter filters are in place. B. Same patient after filling of retinal vessels.

What are the side effects of fluorescein angiography? The side effects include:  Temporary tan skin colour form the dye.  Red after-image from the photoflash.  Discoloration of the urine.  Nausea and vomiting (10%).  Vasovagal synocope (1%)  Anaphylaxis such as bronchospasm, urticarial skin rash and hypotension (<1%).  Cardiac and respiratory arrest (<0.01%).

How do ocular structures determine the distribution of fluorescein angiography? Fluorescein cannot diffuse through tight cellular junctions. These are present at two sites within the fundus: retinal blood vessel endothelium retinal pigment epithelium.  There are two circulation within the fundus: Choroidal circulation –the fluorescein freely leaks out of the fenestrated choroidal capillaries, and from there through Bruch's membrane. however,tight junctions between retinal pigment epithelium (RPE) cells prevents dye reaching the retina Retinal circulation - the retinal blood vessel endothelial cells are joined by tight junctions which prevent leakage of fluorescein into the retina. This constitutes the blood retina barrier. Any leakage from the retinal vessels is abnormal 

1. Capillaries in the ciliary process are permeable to fluorescein, so dye rapidly appears in the aqueous following intravenous injection. 2. Fluorescein in the aqueous and vitreous emits yellow light which reflects off white structures within the eye causing these structures to falsely appear fluorescent. 3. The optic disc, myelinated fibres and hard exudates appear progressively more pseudofluorescent through the course of an angiogram for this reason.

►Indocyanine Green dye is injected into a vein in the patient. As the dye circulates, it passes through the vessels of the retina. Digital fundus photographs are taken to capture the infrared fluorescence of the dye. This technique aids in visualizing the vessels of the Choroid ►Its first application for fundus angiography was by Kogure and others in 1970 when it was used to visualize the fundus of the owl monkey. ►Most clinical ophthalmologists consider ICG angiography to be an adjunctive or secondary test which adds information to the clinical picture and a fluorescein angiogram. ►The recent interest in this procedure has been the result of two factors: the development of digital systems which let us see the choroid, and the interest of ophthalmologists in very carefully directed laser treatment in order to destroy the smallest amount of working retina.

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Physical properties of ICG

Indocyanine green absorbs and reflects in the near infrared portion of the spectrum (805 nm and 835 nm, respectively). It has a peak spectral absorption at about 800 nm. ICG has a half-life of 150 to 180 seconds It is removed from circulation exclusively by the liver to bile juice

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Why is it used ? §Improved imaging of the choroidal circulation. §The most practical clinical application of the procedure has been in those patients with age related macular degeneration (ARMD). §In situations where the source of leakage may be obscured by a hemorrhage of the retina. §Pinpointing the location of the leakage.

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Indications #Age-related macular degeneration #Choroidal polypoidal vasculopathy #Choroidal haemangiomas.

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Side Effects Side effects are minimal.

Patients allergic to iodine or shellfish, or those w a history of liver disease, should advise their physician.

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Choroidal filling defect in early phase ICGA (arrow)

Irregular filling of the choriocapillaris in early phase ICGA

ICG leakage from choroidal vessels in early phase ICGA

Comparison between FFA and ICGA 1.

The difference between fluorescein and ICG angiography is primarily in the type of dye that is used: a.

b.

Fluorescence •

The green ICG dye "fluoresces" and, unlike the dye used in the fluorescein procedure, allows the camera to see through blood, fluid, and pigments that obscure certain conditions from view.

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The fluorescing quality of the ICG dye also allows special digital cameras to capture and view images as the test is being done.

Protein affinity •

Fluorescein (molecular weight 376) is 80% protein bound; the unbound fluorescein readily escapes through the fenestrations of the choriocapillaris and obscures the details of the underlying choroid.

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ICG is a tricarbocyanine dye (molecular weight 775) which is highly protein bound and does not readily escape from the choriocapillaris.

2.

FFA is the accepted standard for imaging the retinal vascular and choroidal circulations

3.

ICGA is especially helpful in situations where the source of leakage may be obscured by a hemorrhage of the retina

4.

High-speed ICGA dynamic imaging can identify feeder vessels and retinal choroidal anastomoses, ensuring safer treatment of choroidal neovascularization

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(A) Hyperfluorescent spots in the late phase of ICGA. (B) These spots cannot be seen on FA

(A) Hypofluorescent spots in the late phase of ICGA. (B) These spots cannot be seen on FA

Early phase of indocyanine green angiography

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