When to Use Indocyanine Green Angiography？

Vascular layer of the eye

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The choroid, also known as the choroidea or choroid coat, is a part of the uvea, the vascular layer of the eye. It contains connective tissues, and lies between the retina and the sclera. The human choroid is thickest at the far extreme rear of the eye (at 0.2 mm), while in the outlying areas it narrows to 0.1 mm.[1] The choroid provides oxygen and nourishment to the outer layers of the retina. Along with the ciliary body and iris, the choroid forms the uveal tract.

The structure of the choroid is generally divided into four layers (classified in order of furthest away from the retina to closest):

• Haller's layer &#; outermost layer of the choroid consisting of larger diameter blood vessels;[1]
• Sattler's layer &#; layer of medium diameter blood vessels;[1]
• Choriocapillaris &#; layer of capillaries;[1] and
• Bruch's membrane (synonyms: Lamina basalis, Complexus basalis, Lamina vitra) &#; innermost layer of the choroid.[1]

Blood supply

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There are two circulations of the eye: the retinal (in the retina) and uveal, supplied in humans by posterior ciliary arteries, originating from the ophthalmic artery (a branch of the internal carotid artery).[2] The arteries of the uveal circulation, supplying the uvea and outer and middle layers of the retina, are branches of the ophthalmic artery and enter the eyeball without passing with the optic nerve. The retinal circulation, on the other hand, derives its circulation from the central retinal artery, also a branch of the ophthalmic artery, but passing in conjunction with the optic nerve.[3] They branch in a segmental distribution to end arterioles and not anastomoses. This is clinically significant for diseases affecting choroidal blood supply. The macula responsible for central vision and the anterior part of the optic nerve are dependent on choroidal blood supply.[4] The structure of choroidal vessels can be revealed by optical coherence tomography, and blood flow can be revealed by Indocyanine green angiography, and laser Doppler imaging.[5]

In bony fish

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Teleosts bear a body of capillary adjacent to the optic nerve called the choroidal gland. Though its function is not known, it is believed to be a supplemental oxygen carrier.[7]

Mechanism

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Melanin, a dark colored pigment, helps the choroid limit uncontrolled reflection within the eye that would potentially result in the perception of confusing images.

In humans and most other primates, melanin occurs throughout the choroid. In albino humans, frequently melanin is absent and vision is low. In many animals, however, the partial absence of melanin contributes to superior night vision. In these animals, melanin is absent from a section of the choroid and within that section a layer of highly reflective tissue, the tapetum lucidum, helps to collect light by reflecting it in a controlled manner. The uncontrolled reflection of light from dark choroid produces the photographic red-eye effect on photos, whereas the controlled reflection of light from the tapetum lucidum produces eyeshine (see Tapetum lucidum).

History

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The choroid was first described by Democritus (c.&#;460 &#; c.&#;370 BCE) around 400 BCE, calling it the "chitoon malista somphos" (more spongy tunic [than the sclera]).[8] Democritus likely saw the choroid from dissections of animal eyes.[9]

About 100 years later, Herophilos (c. 335 &#; 280 BCE) also described the choroid from his dissections on eyes of cadavers.[10][11]

Clinical significance

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Choroid is the most common site for metastasis in the eye due to its extensive vascular supply. The origin of the metastases are usually from breast cancer, lung cancer, gastrointestinal cancer, and kidney cancer. Bilateral choroidal metastases are usually due to breast cancer, while unilateral metastasis is due to lung cancer. Choroidal metastases should be differentiated from uveal melanoma, where the latter is a primary tumour arising from the choroid itself.[12]

See also

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Additional images

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• Schematic cross section of the human eye; choroid is shown in purple.

• Laser Doppler imaging of retinal and choroidal blood flow

• Iris, front view

• The terminal portion of the optic nerve and its entrance into the eyeball, in horizontal section

• The interior of the posterior half of the left eyeball

• Structures of the eye labeled

• This image shows another labeled view of the structures of the eye

• Calf's eye dissected to expose the choroid: its tapetum lucidum is iridescent blue

References

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• Histology image: loa &#; Histology Learning System at Boston University

Indocyanine Green Angiography (ICG) is a diagnostic procedure that uses ICG dye to examine the blood flow in the CHOROID &#; the layer of blood vessels which lies underneath the retina.

Indocyanine Green dye is injected into a vein in the arm/hand. As the dye passes through the blood vessels of your eye, photographs are taken to record the blood flow.

The choroidal vessels are hidden beneath a layer of pigmented cells. Infrared light given off by ICG dye can be imaged through the pigmented layer using special filters.

The most common application of indocyanine green angiography is the detection of choroidal neovascularization, a common component of age related macular degeneration.

In multiple inflammatory conditions, as well as with central serous chorioretinopathy, distinct ICG patterns have emerged that may facilitate better understanding of the disease processes.

What will you experience?

The actual procedure will take 10-20 minutes. The average length of stay in our department can be 1-2 hours.

The Indocyanine Green dye is generally tolerated without any problems. However, ICG dye contains iodine. Severe allergic reactions are possible in people who are allergic to iodine. Our nurse will review your medical history to ensure you are not allergic to substances that contain iodine, such as x-ray dyes and shellfish. ICG dye does not cause urine or skin discoloration.

Your pupils will be dilated for the ICG.

After the pupils are dilated your vision may become blurred. Driving is not recommended when your pupils are dilated.

Before the procedure

EAT, DRINK & TAKE your medications as you usually do.

DRINK an extra 2-3 cups of water before the procedure.

AVOID coffee, tea, or caffeinated beverages.

BRING an English translator.

BRING your lens case, if you wear contact lenses, as you will need to remove the contacts.

Choroid - Wikipedia

Indocyanine Green AngiographyIndocyanine Green Angiography | Department of Ophthalmology