It has been said that the eyes are the window to the soul. Thanks to medical research, it can now be said that the retina is a window to overall health. Research at the National Eye Institute (NEI), Johns Hopkins University, and Massachusetts Eye and Ear, demonstrates how the retina can be both a therapeutic target and a predictor of a person’s risk of developing various diseases.
A study done at NEI and Johns Hopkins University found dysfunction in how cells in the retina remove waste. Scientists found that changes in a factor called AKT2 affect organelles called lysosomes, leading to the production of deposits in the retina, known as drusen. Drusen are a sign of dry age-related macular degeneration. According to researchers, this suggests that the formation of drusen is a downstream effect of AKT2-related lysosome dysfunction. This dysfunction could serve as a therapeutic target.
Lysosomes play an important role in maintaining the retina since they are the cells’ garbage disposal. Additionly, cells that make up the retinal pigment epithelium collect and process wastes through lysosomes. When the cells can’t process waste, drusen forms. As age-related macular degeneration develops, drusen increase in number and volume. Yet, the precise mechanism behind drusen formation remains a mystery.
To find out how drusen forms, scientists manipulated the expression levels of AKT2 in the retinal pigment epithelium of lab mice. When the AKT2 levels were increased, the lysosomes couldn’t function normally, and the mice developed dry age-related macular degeneration symptoms, like retinal pigment epithelium degeneration. Scientists observed similar features in the retinal pigment epithelium cell from human donors with age-related macular degeneration. In fact, cells from donors with a gene variant called CFH Y402H, which increases the risk of age-related macular degeneration, had greater expressions of AKT2. This, in turn, lead to defective lysosomes and drusen deposits.
Since there is no treatment for age-related macular degeneration, the findings from this study could lead to potential treatments for the disease—especially considering that individuals with dry age-related macular degeneration develop drusen in the macula, the part of the retina responsible for central vision.
Moving on the other diseases, it is well known that diseases such as diabetes, heart disease and hypertension can be detected by way of a vision exam. Usually, it is the blood vessels in the eye that sound the alarm for these diseases. Is there another part of the eye that can be used to predict disease risk? Research at Massachusetts Eye and Ear has found that retinal imaging can predict numerous diseases.
What scientist did at Massachusetts Eye and Ear was combine retinal imaging, genetics and big data to find out how likely a person is to develop ocular and systemic diseases in the future. They discovered associations between the thinning of different retinal layers and an increased risk of developing ocular, cardiac, pulmonary, and metabolic diseases.
Thanks to its position in the eye, it is easy to get non-invasive images of the retina. Since retina imaging is routine in ophthalmology, it is possible that one day retina images could be used to screen for diseases. For example, if a person’s retinal image suggests a risk of developing cardiovascular disease, he or she could be referred to a specialist for preventative treatment.
In order to identify associations between retinal health and disease risk and identify genes associated with retinal health, researchers analyzed data from over 44,000 UK Biobank participants who had optical coherence tomography imaging done of their retinal in 2010 and were followed for disease development for an average of 10 years. This study didn’t just look at the genes linked to retinal health; it went deeper to find out about the role of different cell layers that make up the retina.
Each layer of the retina consists of different cell types with distinct structures and functions, and researchers found that the thickness of the different layers are associated with different conditions. Also, the study provided insights into the genes and biological pathways that regulate retinal health, which could be leveraged for future treatments.
While earlier studies showed that there are links between retinal health and diseases such as diabetes and hypertension, this study showed that retinal images have more health information than previously thought. One important discovery from this study was that many health conditions —including poor cardiac, metabolic, pulmonary, and renal function—are linked to thin photoreceptors in the retina. Of course, further studies are needed, particularly those that replicate the study’s methods with a more diverse population, as the UK Biobank participants were predominantly white and between the ages of 40 and 70 at the study’s outset.
The eyes have it—not just for vision, but for disease detection as well.
https://www.aao.org/eye-health/tips-prevention/surprising-health-conditions-eye-exam-detects