The eye is more than a window to the soul — it is also an early warning system for the human body. The eye’s anatomy and the behavior of its blood vessels alert physicians to problems, such as high blood pressure or diabetes, that affect other organs and organ systems. Advanced imaging tools provide a means to use the accessibility of the eye for such purposes.
In the 21st century, a new dimension of advanced imaging was introduced to ophthalmology: movement. Specifically, the ability to image the movement of blood in patients in real time. Wilmer retinal specialist Adrienne Scott is an expert in using these images, which are captured through optical coherence tomography angiography [OCTA].
Scott’s area of research is sickle cell retinopathy, a condition that can afflict those who have sickle cell disease, the most common inherited blood disorder. Sickle cell disease affects hemoglobin — a protein in red blood cells that carries oxygen throughout the body. Red blood cells are usually disc-shaped and flexible, which facilitates smooth blood flow and oxygen delivery in the body. An effect of sickle cell disease is that red blood cells become shaped like sickles, or crescents, and are not as flexible, which can block blood flow, leading to strokes, eye problems, infections or pain crises.
“One of the unique aspects about being a retina specialist is that we can image the blood vessels easily through a dilated or even an undilated pupil in a noninvasive fashion,” says Scott. With OCTA, retina specialists can also image the lack of blood flow through those vessels. “Patients who have sickle cell disease can have evidence of decreased oxygenation caused by decreased circulation and blood flow in their retinas even from a very young age,” says Scott.
According to Scott, this impaired blood flow in the retina does not seem to affect vision early in the disease, but imaging blood flow in the eyes can hold a clue to impaired blood flow in other parts of the body. “Because sickle cell is a systemic disease, it affects every organ system from the head to the toe,” she says. A view into this blood flow is valuable, especially if researchers can connect lack of blood flow in an organ that is easy to image — the eye — with lack of blood flow in another organ that is not easy to image, like the brain.
Children with sickle cell disease are prone to getting strokes because of abnormal oxygenation of the blood, she says, particularly a type of stroke called a silent infarct, which is a blood flow stoppage without a neurologic abnormality. Because of this, part of the standard of care for patients with sickle cell disease is to have regular MRIs. By examining the OCTA scans and MRIs of patients, Scott hopes to answer the question: “Can we look at these retinal blood flow areas and get a sense of absence of blood flow in the brain? And is there a link between patients who’ve had loss of blood flow in areas of the retina and their incidence of stroke?”
If so, then the lack of retinal blood flow could be a homologue for lack of blood flow in certain areas of the brain, and imaging retinal blood flow could be a proxy for the more difficult imaging required for MRIs — particularly in the case of young children who often need to be sedated for MRIs.
“There are certain reasons why we think the retinal blood vessels that we see in the eye every day with our dilation and those in the brain may have some connection: Both the retina and the brain have a similar embryonic origin in the way the tissues developed,” says Scott. Both also have watershed zones, which are unique places related to blood flow present in some organs. A watershed zone lies on the edges of two different areas of blood circulation each supplied by a main artery on the opposite side of where the watershed zone sits. The tiny overlap between the two areas is the watershed zone. Because that zone is the farthest away from each of the main arteries that feeds it, the zone has the weakest blood flow in both directions.
“A watershed zone is very vulnerable. It relies heavily on both those areas to function well, and if something goes wrong and the blood supply is diminished, then it’s very vulnerable to infarction or damage from loss of blood flow,” says Scott. The eye and the brain are not the only organs with watershed zones; they exist in the kidneys and in the intestines as well.
Insights into how blood moves through a watershed zone in an easily accessible organ like the eye could yield insights into watershed zones throughout the body — further demonstrating the indispensability of the eye to gaining a clear picture of our overall health.