In macular degeneration, the macula becomes damaged. The macula is the most sensitive part of the retina and is located in the back of the eye. Certain cells that make up the macula sense light and enable you to have sharp central vision.1 If your macula is damaged, you may notice blind spots, blurry spots, or black/dark spots in your central vision. Because the macula is located in the back of the eye, it’s not always easy to examine the macula – although there are a variety of imaging tests that allow your doctor to take a closer look.
Indocyanine green (ICG) angiography is one of these tests; it involves the use of a special dye and a camera to track the flow of blood through blood vessels in the back of the eye. In particular, ICG is used to examine the blood vessels in the choroid, which may be abnormal in those with wet AMD.
What is indocyanine green angiography?
Indocyanine green angiography is especially useful for looking at the blood vessels in the choroid. The choroid is an important layer of blood vessels and connective tissue located between the white of the eye (the sclera) and the retina. The choroid supplies nutrients to the outer layers of the retina, while the retinal blood vessels supply nutrients to the inner layers of the retina.2 ICG is similar to fluorescein angiography (FA), but instead of using sodium fluorescein, it uses indocyanine green dye, which lights up under infrared light. When an infrared sensitive camera is used, ICG dye circulating in choroidal blood vessels are highlighted.
During the test, ICG dye is injected into a vein in your arm, which then travels through the bloodstream to reach the eye. Unlike fluorescein dye, which leaves the eye quickly, ICG dye is bound by proteins in the bloodstream that cause it to stay in the retinal and choroidal vessels longer, allowing for more detailed imaging.2 Because the choroid is located underneath the retinal pigment epithelium, a pigmented layer of cells, an infrared camera with a special filter is used to obtain images of the ICG dye flowing through choroidal vessels.3 The whole process takes approximately 10 to 20 minutes.
Risks
Your eye will be dilated for ICG angiography, so it might be sensitive to light. You may also need someone to take you home afterward because your vision may be blurry from dilation. Rarely, one may develop an allergic reaction to the dye because it contains iodine. Prior to ICG angiography, talk with your doctor about any drug allergies you might have, or if you have had an allergic reaction to iodine or any other contrast dyes from previous imaging studies. He/she might recommend another test instead or may deem that it is safe to proceed despite the prior reaction.
Unlike fluorescein dye, ICG dye will not alter the color of your skin or urine.3
What can you do?
If you have macular degeneration, talk with your doctor about whether ICG is an appropriate imaging test for you. Depending on your macular degeneration, your doctor may recommend undergoing ICG in conjunction with FA to obtain a more comprehensive picture of your eye condition, disease course, or treatment response. Together, you and your doctor can decide on the most appropriate methods for monitoring your macular degeneration.