Indocyanine green (ICG) angiography is a diagnostic test that provides a detailed view of blood circulation within the eye by injecting a fluorescent dye into the bloodstream. A specialized infrared camera captures images as the dye flows through the ocular blood vessels. This technique is effective for visualizing the choroid, a deep layer of blood vessels behind the retina. The ICG dye can be seen through pigment and fluid that might obscure other imaging methods, offering a clear picture of the choroidal structures.
Clinical Applications of ICG Angiography
This imaging technique helps diagnose and manage several complex eye conditions. One of the primary applications is for “wet” age-related macular degeneration (AMD), where abnormal blood vessels grow under the retina. ICG angiography excels at detecting this choroidal neovascularization, providing a clearer view of these damaging vessels.
Another condition where ICG angiography is beneficial is polypoidal choroidal vasculopathy (PCV), a disorder involving abnormal, grape-like dilations of blood vessels in the choroid. The detailed imaging allows for the precise identification of these polypoidal structures to guide treatment decisions. For central serous chorioretinopathy, a condition causing fluid to leak under the retina, ICG can help pinpoint the exact location of the leakage from the choroidal layer.
The test is also used to evaluate ocular inflammatory diseases, sometimes referred to as uveitis. Inflammation can affect the choroidal vessels, and ICG angiography can reveal the extent of vascular involvement, helping to assess the condition’s severity and monitor treatment. In conditions like serpiginous choroidopathy, the test can identify active choroidal lesions not visible with other examination techniques.
The Angiography Procedure
The ICG angiography procedure is completed within about 30 minutes. It begins with the administration of eye drops to dilate the pupils, which takes approximately 20 to 30 minutes to take full effect. This widening ensures the camera has a clear view for imaging.
Once the pupils are dilated, a small amount of the indocyanine green dye is injected into a vein, usually in the patient’s arm or hand. The patient is then seated in a darkened room with their chin on a rest and forehead against a support bar to keep their head still. A specialized camera then begins taking a series of photographs as the dye circulates into the vessels of the choroid and retina.
During the imaging sequence, the patient will see a series of bright flashes of light from the camera. The photographer may ask the patient to look in different directions to capture various angles of the retina and choroid. This sequence of pictures tracks the dye’s path, showing how blood vessels fill and if any dye leaks.
Preparation and Potential Risks
Patients should inform their doctor of any known allergies, especially to iodine or shellfish, as this can indicate a higher risk of a reaction to the ICG dye. It is also necessary to provide a complete medical history, including any pre-existing liver or kidney conditions, as these organs process and clear the dye from the body.
Since the pupils will be dilated, vision will be blurry and sensitive to light for several hours afterward. Patients must arrange for someone to drive them home from the procedure. Drinking plenty of fluids after the test can help flush the dye from the system more quickly.
While the procedure is generally safe, potential side effects exist. It is common for the skin to take on a temporary yellowish tint and for urine to appear dark for a day or two as the body excretes the dye. Some individuals may experience mild nausea during the injection. A more serious, though rare, risk is an allergic reaction, which can range from skin rashes to severe anaphylactic responses.
Understanding the Angiogram Results
After the images are captured, an ophthalmologist analyzes them for abnormalities in choroidal blood flow. The interpretation centers on identifying areas of “hyperfluorescence” and “hypofluorescence.” These terms describe how brightly the dye glows in the images compared to the surrounding tissue.
Hyperfluorescence refers to areas that appear brighter than normal, which often indicates leaking from abnormal blood vessels. This is a common sign in conditions like wet AMD or PCV, where new, weak vessels allow the dye to seep out. The pattern, location, and timing of the bright spots help the doctor pinpoint the problem’s source.
Conversely, hypofluorescence describes areas that are darker than normal. This can suggest a blockage in blood flow, preventing the dye from reaching a particular area of the choroid. It can also occur if something is obscuring the view of the dye, such as an area of hemorrhage or dense pigment on the retina. By mapping these patterns, the ophthalmologist can diagnose the condition and plan treatment.