This article is more than 5 years old. Information may no longer be current.
ICG, fluorescein: complementary tests
Since being introduced several years ago, indocyanine green angiography (ICG) has become an important tool in diagnosing and evaluating eye diseases. It is intended to complement, rather than replace, fluorescein angiography.
“This is an important point,” said Bert M. Glaser, MD, of the Glaser-Murphy Retinal Treatment Center in Towson, Md. “One is not a replacement for the other. They provide different pieces of information. They augment one another and make each one more powerful,” he said.
Mark Dunbar, OD, director of optometric services at Bascom Palmer Eye Institute, agreed. “Generally, you wouldn’t do an ICG over fluorescein. You’ll almost always do fluorescein. The question is, do you also do an ICG?
“ICG has been shown to be effective with some choroidal processes. Any time you want to see what’s going on with the choroid, ICG is going to be used. You can actually do them both at the same time,” he added.
Fluorescein, a tried and true method
Dr. Glaser explained that fluorescein provides the practitioner with basic information. “It gives you a lot of information about the retinal vasculature and an overview of the status of the choroidal circulation: where things are leaking, where there are window defects and where there is blockage,” he said. “When you are looking at diabetic retinopathy — vein and artery occlusions, for instance — you are going to be mostly dealing with a fluorescein angiogram.”
Dr. Dunbar said, “You use it with retinal vasculature disease such as in diabetic retinopathy or vein occlusions. It can be used not only for diagnostic purposes, but to determine where treatment should be applied in diabetic retinopathy or with neovascularization. You can do a fluorescein to determine what the capillary bed is like, especially in the macula, to find out how well it’s profused.”
Fluorescein angiography can also be used to look for the risk of developing ischemia or neovascularizations in both branch and central vein occlusions. “Any time you see fluid in the macula,” Dr. Dunbar said, “fluorescein angiography should be used to try to figure out the cause of the fluid. It could be choroidal neovascularization or even retinal telangiectasias. Fluorescein is a valuable tool in diagnosing retinal disease.”
When to order an ICG
ICG is most beneficial when looking at choroidal circulation and is particularly useful in finding subtle leakage. “ICG gives you a lot more information as to where things leak,” said Dr. Glaser. “It is usually better for slower leaks than fluorescein angiography. Also, there is a new high-speed component that is very good for dissecting out the vasculature filling patterns and the actual abnormal new vessels in the choroid.”
ICG can also be used to identify idiopathic polypoidal choroidal vasculopathy, according to Dr. Dunbar. “This is a condition we are beginning to hear more about,” he said. “It involves the sanguineous choroidal vessels. It mimics age-related macular degeneration a bit, but usually we see this more in African-American patients.
“In lupus choroidopathy, the patient experiences an occlusive process within the choriocapillaris that leads to serious detachments,” Dr. Dunbar continued. “You would want to do ICG to look at the choroidal vasculature to see if there is any hypoxic or occlusive phenomenon.”
ICG is also being used to help differentiate choroidal tumors, Dr. Dunbar said. “Choroidal melanomas tend to block the ICG, whereas choroidal hemangiomas tend to slowly hyperfluoresce throughout the ICG,” he said.
Dr. Dunbar added that ICG is still in the discovery stages. “The key with ICG is that, because of the absorption characteristics of the eye, you are looking at the infrared spectrum of wavelength, so that really allows you to get a better view of the choroid,” he said. “If you have a patient who has a subretinal hemorrhage or a lot of pigment, the transmission characteristics of the dye allow it to filter through, providing better choroidal detail. That’s really the big advantage.”
High-speed ICG
Phi-motion angiography is a new high-speed ICG method, said Dr. Glaser. “You can use ICG with newer, high-speed systems, which go up to 40 frames per second, whereas before we could only get one frame every 3 or 4 seconds,” he said. “It will allow us to have real breakthroughs in the treatment of macular degeneration. Now we can see the feeder vessels that feed the individual leaking areas.”
Dr. Glaser explained that by using a pinpoint laser to close the feeder vessel with “a fraction of the amount of laser used for other treatments, away from the center so the risk is extraordinarily low, we can see dramatic improvement in vision. The high-speed ICG has only been around for a few years, and it’s only been perfected over the last year and a half. Now, you can run it on a regular desktop computer in a Windows-based system.”
For Your Information:
- Bert M. Glaser, MD, is a member of the Editorial Board of Primary Care Optometry News. He can be reached at the Glaser-Murphy Retinal Treatment Center, 901 Dulaney Valley Rd., Ste. 200, Towson, MD 21204; (410) 337-4500; fax: (410) 339-7326; e-mail: mdretina@earthlink.net; Web site: www.glasermurphyretina.com.
- Mark Dunbar, OD, is director of optometric services at Bascom Palmer Eye Institute, University of Miami School of Medicine. He can be reached at 900 NW 17th St., Miami, FL 33136; (800) 329-7000, ext. 4042; fax: (305) 326-6113.