Eye and the Brain
An eye oftentimes feels like the most underappreciated systems in the field of vascular biology. An eye is a highly vascular organ than it gets credit for, and here’s why – ranging from high blood pressure or diabetes to early signs of stroke, an eye exam can, in fact, tell a physician a lot about one’s health. In a series of blog posts, I decided to highlight these key connections between the eye and the human body. This article will focus on the current knowledge linking eye and the brain.
One of the common cerebral diseases caused by blood vessels is stroke. Stroke, typically caused by a blood clot, can either be a chronic or acute ischemic complication. This eventually leads to loss of function in the brain and hemorrhaging (bleeding) in the related part of the brain, retina, or spinal cord. Many risk factors shared by cardiovascular diseases converge with risk factors for stroke. For example – hypertension, diabetes, and alcohol consumption can all increase incidence of stroke related problems.
In my previous blog, I explained how retinal microvessels can be a window to the vessels in the body. Dimensions like caliber (diameter) of retinal vessels can be measured noninvasively, and how they strongly correlated with cardiovascular risks. This article will focus on how, this is also resonant in case of vessels of the brain (cerebrovascular). Physiologically and anatomically, vessels in the retina and the brain share many similarities. Most commonly known would be the blood-brain barrier and the retinal-blood barrier, maintained by tight junctions that are essentially bouncers found outside a club. Even with advanced imaging technologies, capturing these neurovessels can be very challenging. Serendipitously, retinal photographs can thus be used to provide information like signs of stroke or predictors of stroke or dementia, as detailed in this article. Retinal fundus photograph of a patient (as seen in picture) shows embolism or blockage caused by cholesterol-like deposits, and are strongly associated with increased risk of stroke-related death as detailed in a study.
One study, specifically the measurements of retinal vessels and compared its association with acute ischemic stroke in a population study. Even the subtlest changes in the retinal vessels of stroke patients were reported, which stood out on comparison with healthy patients. Interestingly, changes in dimensions of retinal vessels were also found in patients with dysfunction in cognitive behavior, suggesting similar tests can be used to diagnosing diseases like dementia and Alzheimer’s (more on this in future posts). Another common indicator between stroke and the retina was found in the retinal nerve fiber layer. Although this is slightly different than comparing the blood vessels, a research group found strong correlation between defects in the nerve fiber layer and acute stroke.
In conclusion, many research groups are now considering using tools to assess retinal vessels for diagnosis of cerebrovascular diseases. More studies in this area, can then suggest a very powerful and noninvasive diagnostic method, which could help both the patient population and the clinicians.