ICG is a special dye used to acquire an angiogram of a part of the eye known as the choroid. ICG is injected intravenously into the patient’s bloodstream during an ICG angiography. An ICG angiography is an eye test that is conducted to take images of the choroid.
The choroid is a layer located in the posterior part of the eye, which contains a unique network of blood vessels. The blood vessels carry nutrients to the eyes’ photoreceptors (rods and cones). Another role that the blood vessels play is temperature control within the eye because they flow very fast. However, with age, these blood vessels tend to get affected by diseases.
Also Known As
- Choroidal angiography
- Indocyanine Green Angiography
ICG angiography is an eye test that has to be conducted by a specialist. This is because ICG can only be prescribed and administered into the patient’s bloodstream under the supervision of a doctor. These specialists are:
- Nurse with an ophthalmic medical photographer
ICG is a fluorescent, cyanine dye that glows under infrared light. This means that when a photograph of it is captured, we can see through pigmentation, fluid, or blood in the back of the eye. It also means that the naked eye cannot see ICG as the test is being conducted.
Once the dye is introduced into the bloodstream, it travels to the eyes. As it passes through the blood vessels, a unique infrared camera takes images of the retina and the choroid.
ICG is used by doctors to diagnose or find problems in the patient’s blood vessels, blood flow, and tissue perforations. It is then metabolized in the liver and excreted into the bile.
ICG angiography is mainly used to diagnose macular degeneration. This refers to loss or blurred vision in the central periphery. The test is used to help diagnose and check on other progressive retinal diseases such as:
- Retinal vein occlusions - Blockage of the small veins located in the retina.
- Cystoid macular edema - Cyst-like areas of fluid in the macula that cause retinal swelling.
- Diabetic retinopathy - Damage to the retina’s blood vessels.
- To gauge areas of the retina that need treatment before laser eye surgery.
A complementary test to the ICG angiography is fluorescein angiography that uses the same technique, but instead of ICG, it uses the fluorescein dye. However, ICG differs from fluorescein angiography as its nature allows it to stay in the retina and choroid, allowing the choroid’s blood vessels to be seen more clearly.
Preparation & Expectation
There are a few things that the patient is required to do a few hours before the test. S/he is asked to drink 3 cups of water before the procedure. S/he is also requested to avoid drinking tea, coffee, or any other caffeinated beverages. The client is required to bring their glasses or contact lenses but will need to remove them during the procedure. They should also bring any medication that they’re currently taking.
The test may cause blurred vision. Therefore, it is recommended that the patient bring someone to drive them home once the procedure is done. The patient is also advised to bring with them a pair of sunglasses to wear because their eyes will be sensitive to light. Apart from the prick of the needle when injecting ICG, the procedure is mostly painless.
- ICG contains iodine. Therefore, the eye doctor may opt to test whether or not the patient is allergic to iodine or other iodine-containing substances.
- The nurse will administer dilating eye drops to widen the pupils. After a little while, a second set of drops are administered. A well-dilated retina is required to get a full view of the retina.
- The patient is then asked to sit as comfortably as possible at a fundus machine. This is a unique machine which is used to take the pictures.
- After this, the dye is introduced into the patient’s bloodstream through their arm or hand via an IV needle.
- As soon as the ICG dye is injected, photographs are taken. The photos map out the dye’s movement. The images use different coloured lights as the ICG passes through the blood vessels of the eyes.
- After a few minutes, the patient will sit back to allow the pooling of ICG in the eye. Then more photographs are taken.
- The photographs are taken at timed intervals. No X-rays or radioactive materials are used. The test lasts about 30-minutes.
- The doctor may opt to keep the patient for a short while for monitoring and observation. After a short rest, the patient will be able to go home.
The eye specialist may be able to discuss the results on the same day.
There are no delays, obstructions, or leakages monitored as the dye flows through the eye’s blood vessels.
Abnormal results may indicate the presence of:
- Choroidal tumours
- Abnormal blood vessels
- Leaking or blocked blood vessels
- Diabetic retinopathy
Risks & Complications
The side effects felt by the patient are minimal and are usually no cause for alarm. Common side effects include:
- Pruritus-The patient may feel a tingle/slight sensation at the injection site that occurs within 30 minutes of the injection.
- Nausea may occur for a few minutes.
- Blurry vision due to the dilating eye drops administered.
- Sensitivity to light due to the bright camera flashes.
- Diabetic patients could experience false higher than normal glucose readings.
These effects are temporary and will wear off in a few hours. Allergic reactions can be managed with antihistamines, depending on the gravity of the side effect. If the effects don’t wear off after a while, the patient is advised to consult their doctor.
However, severe reactions have occasionally been reported, with 1 out of 300,000 deaths reported following an ICG test. Severe side effects include:
- Vaso-vagal reaction (Fainting)
- Severe allergic reactions
- Urticaria - These are itchy hives, usually on the head and face.
- Heart attack
- Difficulty breathing
In the rare case that the patient experiences any of the above, they should be rushed to the hospital immediately.
Expectant women and breastfeeding mothers should avoid taking the test because the effects on the unborn and newborn are still unknown.