Overview of Orbital Color Doppler Imaging
Color Doppler imaging (CDI) is a harmless technique used for creating a colorful, two-dimensional picture of the blood vessels in our body. It’s often used to look at the blood supply to the eye, helping to diagnose, predict the outcome, and monitor certain eye-related diseases. CDI is especially useful in understanding how different eye diseases form and progress. It mainly looks at the blood vessels supplying the eye, which come from the carotid arteries in your neck. The blood flow to the eye is controlled by the nervous system and certain chemical signals, and can change based on what’s going on in your body.
There are 5 key things that CDI looks at: Doppler indices (a measurement of blood flow), the central retinal artery (a blood vessel that feeds the eye), the ophthalmic artery (another blood vessel that feeds the eye), the short posterior ciliary arteries (small blood vessels that supply the back of the eye), and the superior ophthalmic vein (a vein that drains blood from the eye).
CDI uses these measurements to help diagnose several eye conditions including but not limited to persistent fetal vasculature (a birth defect in the eye), tumors inside the eye, blockage of the arteries, glaucoma (a disease that damages the optic nerve), diabetic retinopathy (an eye problem in people with diabetes), and vascular malformations (abnormal connections in the blood vessels). Even though CDI is a helpful tool, there is still ongoing research to understand additional uses for it.
Anatomy and Physiology of Orbital Color Doppler Imaging
The arteries and veins that supply blood to the area around the eye, known as the orbit, can look different from person to person. Most often, the blood comes from the internal carotid artery, with a smaller amount coming from the external carotid artery.
The main artery that provides blood to the orbit is called the ophthalmic artery. This artery is located in the head and is the first one that branches off the internal carotid artery. The ophthalmic artery enters the orbit through a small opening called the optic canal, which is positioned next to the optic nerve. It gives rise to the central retinal artery, which supplies blood to the back portion of the eye, and then crosses to the top inner portion of the optic nerve. There are a number of other smaller arteries that supply blood to the different parts of the eye. The ophthalmic artery finally ends near the top inner edge of the orbit, where it splits into two arteries.
The external carotid artery also contributes to the supply of blood to the orbit through the infraorbital artery and another branch stemming from an artery called the middle meningeal artery.
The system of veins in the orbit consists primarily of two veins, named the superior and inferior ophthalmic veins, along with many other different veins. The function of these veins is to carry blood back from the orbit towards the heart. The superior ophthalmic vein drains blood into a cavity called the cavernous sinus, going through a crack known as the superior orbital fissure. The inferior ophthalmic vein can either join the superior ophthalmic vein or drain directly into the cavernous sinus.
The blood flow in the orbit automatically adjusts itself based on the activity of the autonomic nervous system and certain chemical mediators. These include
- Endothelin-1: A strong chemical that can narrow the blood vessels. It affects the blood flow in the choroid, which is a layer in the eye, and can be a risk factor for eye diseases like glaucoma and diabetic retinopathy.
- Nitric Oxide: A molecule that can expand the blood vessels, helping to control the pressure inside the eye and the blood flow during inflammation in the orbit.
- Adenosine: A strong molecule that can modify the pressure inside the eye, causing the blood vessels in the retina, the light-sensitive part of the eye, to expand.
- Oxygen: The level of oxygen in the blood vessels in the retina affects how the blood flow changes to meet the needs of the retina.
- Carbon Dioxide: The level of carbon dioxide in the blood can control the blood flow in the retina since it has a stronger impact on blood flow than oxygen.
Other molecules, such as estrogen and carbonic anhydrase enzyme, may have an unclear role in this automatic regulation process.
Events like exercise and situations that activate the body’s “‘fight or flight’ response” can cause the small arteries in the eye to narrow and reduce the blood flow to the eye.
Why do People Need Orbital Color Doppler Imaging
Orbital color Doppler imaging is a type of test that uses sound waves to create images and assess the flow of blood within the vessels of and around the eyes. These are some of the reasons why a doctor might ask for this test:
For Diagnosis Support:
- Persistent fetal vasculature – a condition where abnormal blood vessels from when a baby was developing in the womb didn’t go away on their own as they should have.
- Intrabulbar tumors – growths or lumps inside the eyeball.
- Arterial occlusion – blockage in one of the blood vessels that nourish the eye.
- Ocular ischemic syndrome – reduced blood flow to the eye.
- Carotid cavernous fistula – an abnormal connection between an artery and a vein in the area behind the eye.
For Prognosis and Monitoring:
- Glaucoma – an eye condition that can cause damage to the optic nerve, often due to high pressure in the eye.
- Thyroid eye disease – an autoimmune condition where the muscles and fatty tissues of your eye become inflamed, often related to an overactive thyroid.
- Diabetic retinopathy – a complication of diabetes that affects the blood vessels of the light-sensitive tissue at the back of the eye (retina).
- Vascular malformations – abnormal clusters of blood vessels.
- Mucormycosis – a rare fungal infection that can affect the sinuses, the brain, or the lungs, and can sometimes spread to the eye.
Indications Still Under Research:
- Age-related macular degeneration – an eye disease that causes vision loss in the center of your field of vision.
- Central retinal vein occlusion – a blockage of the main vein in your retina.
- Central serous chorioretinopathy – a condition that causes a build-up of fluid under the retina.
- Sickle cell disease – a group of inherited red blood cells disorders, which can cause eye complications due to the blockage of blood vessels.
- Behcet disease – a rare disorder that causes inflammation in blood vessels.
- Orbital cysticercosis – a parasitic infection in the eyes.
Scientific studies are currently evaluating the use of orbital color Doppler imaging in these medical conditions in order to validate its effectiveness.
When a Person Should Avoid Orbital Color Doppler Imaging
The only time that doctors should definitely not use orbital ultrasonography or CDI (which are types of medical imaging tests for the eye area) is when a person has previously had a severe eye injury. This includes injuries where something has pierced or gone through the eye, leading to a rupture of the eyeball. These tests could potentially cause more harm in these situations.
Equipment used for Orbital Color Doppler Imaging
For this type of scanning, a particular ultrasound machine is needed, which offers a feature called “duplex mode”. This combines two-dimensional, real-time ultrasound imaging with a technique known as color-coded Doppler imaging. The Doppler technique is used to visualize blood flow within the body in different colors, which help doctors analyze the pattern and speed of blood flow.
The part of the body examined in this case are the blood vessels in the orbit, the bony eye socket containing the eyeball. These vessels are usually viewed at a depth of 1.5 to 4.0 cm in the body. And a specific type of probe—thin rod-shaped tool used to send and receive the ultrasound signals—is used. This probe, referred to as a ‘linear probe’, operates at a frequency of 7.5 to 10 Megahertz (MHz). This means the probe can send and receive millions of ultrasound signals per second, providing a high resolution image.
Who is needed to perform Orbital Color Doppler Imaging?
A highly skilled doctor who specializes in studying images of the body, known as a radiologist, or a doctor specifically trained to look after your eyes, called an ophthalmologist, should be the one to carry out the CDI. The CDI is a test that helps doctors to see how your blood flows and can help them find problems. These doctors have the right training and knowledge to make sure the test is done properly and safely.
Preparing for Orbital Color Doppler Imaging
For a CDI, or Color Doppler Imaging, a few things are needed: an ultrasound machine with a special probe, a special jelly used for ultrasound scanning, and a clear plastic film. The patient should avoid drinking alcohol or smoking at least 12 hours before the test. Using certain eye medications, especially ones for glaucoma, can change the blood flow in the eyes. There are also certain factors like high blood pressure, feeling anxious, having a fast heart rate, an increased heart output, and raised pulse pressure that can affect the blood flow at the back of the eyes. It’s important for the person doing the test to try and limit the impact of these factors on the CDI for the most accurate results.
How is Orbital Color Doppler Imaging performed
Your doctor will ask you to lie down on your back and raise your head a bit. He will then place an ultrasound probe gently over your closed eye to see inside your eye. This is gentle enough not to squeeze the blood vessels in your eye.
In medical terms, there are three important measurements that are often gathered during an ultrasound:
- Peak systolic velocity: This tells the doctor the highest speed at which your blood moves during the phase when your heart contracts (systole).
- End diastolic velocity: This measurement tells the doctor the lowest speed at which your blood moves when your heart is at rest (diastole).
- Resistivity index: This number shows the difference between the peak systolic velocity and end-diastolic velocity. This gives your doctor an idea of blood flow during one complete heart cycle.
There are several different parts of your eye that the doctor will take images of:
- Central retinal artery: This blood vessel is in the optic nerve (the nerve at the back of your eye). It has a rapid flow of blood and requires a small Doppler gate (a tool that measures blood speed) for accurate measurement.
- Ophthalmic Artery (OA): This artery is found on the side of the eye socket and crosses the optic nerve. It has a rapid peak of blood flow and then a sudden drop.
- Short posterior ciliary artery vessels: These small blood vessels are located on the sides of the optic nerve at the back of the eye. They have a low-resistance waveform which means the blood flows smoothly through them.
- Superior Ophthalmic Vein (SOV): This vein can be found in the upper and inner part of the eye socket. The flow of blood in this vein can be affected by many external factors.
The values gotten from these various measurements can vary, so an average is often taken from three separate measurements. There can also be differences between different populations, so studies provide averages based on their specific patient groups.
Possible Complications of Orbital Color Doppler Imaging
Orbital CDI, a medical procedure involving the eye, can lead to issues like pain caused by too much pressure on the eyeball, and potential damage in cases where the eye was previously harmed but not diagnosed. However, when carried out by skilled staff, there have been minimal reported problems.
What Else Should I Know About Orbital Color Doppler Imaging?
Persistent Fetal Vasculature (PFV) is a condition where some blood vessels in the eye, which are supposed to disappear before birth, remain. There are four forms this can take: a straight line (Type I), a Y-shape (Type II), an upside-down Y-shape (Type III), and an X-shape (Type IV). The kind of surgery needed depends on the specific type. Doctors use specialized ultrasound and imaging to guide the surgical process.
A type of eye tumor called choroidal melanoma can have faster blood flow compared to other types of harmless tumors. Doctors use various techniques to monitor the reaction to the treatment for these tumors, which include measuring changes in blood flow.
Sometimes, the blood flow to the eye can become blocked, leading to sudden and painless vision loss. Techniques like ultrasound imaging can help identify these blockages and plan the appropriate treatment.
Difficulty diagnosing a condition called ocular ischemic syndrome can lead to missing out on vital treatment times. It’s a condition where eye tissues don’t get enough blood supply, often due to blocked blood vessels in the neck or the heart. Imaging can identify these issues early on, potentially saving lives.
In a condition called arteritic anterior ischemic optic neuropathy, there is a marked decrease in eye blood flow. Recognizing this condition early can help prevent further damage.
A carotid cavernous fistula is a condition where there’s an abnormal connection between certain blood vessels in the eyes. Monitoring the blood flow in these unusual connections can help guide treatment.
Open-angle glaucoma is a common eye disease that slowly erodes your sight. It happens when the drain structure in your eye — the part that looks like a mesh sifter — becomes less efficient over time, and pressure in the eye slowly increases due to accumulated fluid. Higher resistance to blood flow is usually seen in patients with progressive glaucoma.
Thyroid eye disease can result in changes in the blood flow in the eye. This can be an effective way to monitor the progress of the disease and the effect of treatment.
Diabetic retinopathy is a condition that can occur in those with diabetes. Abnormal blood flow patterns can be seen before any major changes occur in the eye, aiding early diagnosis.
Some blood vessel abnormalities result in unusually high blood flow patterns in the eye. Treatments for these conditions can lead to a reduction in blood flow and can be monitored using Doppler imaging.
Mucormycosis is a serious fungal infection that can affect the eyes. Specific patterns of blood flow can help predict the progress of the disease.
Age-Related Macular Degeneration can cause changes in the resistivity and blood flow in the eyes. Detecting these early provides an avenue for early diagnosis and treatment.
A central retinal vein occlusion is another condition that changes the blood flow in the eyes. Using Doppler imaging can help detect this condition and monitor its progress.
