The eyes have long been called the “windows to the soul,” and increasingly, evidence is suggesting that they might be also windows to both the brain and body. Several health conditions can be detected by examination of the eyes, among them diabetes, multiple sclerosis, and even Alzheimer’s disease. Medical News Today spoke to experts in the field to discover how the eye can reveal the body’s secrets.
Most of us have our eyes tested regularly, but few may be aware that an eye test is not just for checking vision and correcting sight problems.
Because it has a “window” at the front, the eye is the only part of the body where doctors can, non-invasively, examine the inside of an organ. At the back of the eye is the retina, where blood vessels and the optic nerve can be clearly seen.
Thanks to this, optometrists and ophthalmologists could diagnose not only disorders of the eye, but also systemic diseases — those that affect other organs in the body or the whole body.
If a routine eye test raises concerns, the optometrist can refer a person to a medical ophthalmologist who will investigate by carrying out further eye examinations. If their investigations reveal a systemic disease, they can then refer the person to the relevant specialist.
Dr. Hagar Ibrahim, senior specialist trainee (ST6) in medical ophthalmology at St. Paul’s Eye Unit, Liverpool University Hospitals NHS Trust, in the United Kingdom, told Medical News Today that “a routine eye examination in which the pupils are dilated using eye drops can provide a full and clear view of the optic nerve, which connects to the brain, the retina, […] and all the blood vessels supplying the retina.”
“Therefore, pathology in the eye can be clearly seen during [an] eye examination, both in localized eye conditions and in systemic disease, truly making the eye a window into the rest of the body,” she added.
What can be diagnosed?
“People are often surprised when an eye doctor diagnoses them with a systemic illness but they shouldn’t be. Many people with systemic illnesses are first diagnosed by their eye doctor, which is just one reason why all adults should have regular eye examinations at least every 2 years.”
– Dr. Philip Storey, a board-certified ophthalmologist and fellowship-trained retina specialist at Austin Retina Health
As well as identifying problems with vision, such as nearsightedness, farsightedness, and astigmatism, a routine eye test will detect other eye disorders, such as glaucoma, and age-related macular degeneration.
By examining the blood vessels in the retina and the optic nerve, the optometrist can also discover a lot about a person’s general health.
This non-invasive process can detect many other health conditions that may seem unconnected to the eyes, among them hypertension, diabetes, thyroid disorders, and neurodegenerative diseases such as Alzheimer’s disease, and multiple sclerosis (MS).
“Ocular inflammation can affect many parts of the eye, and can often be the first sign of a systemic disease. The key to diagnosing the cause is in focused history taking followed by [a] guided investigation of the relevant body systems, including blood tests,” explained Dr. Ibrahim.
Blood vessel changes
Changes in the blood vessels in the retina can be early indicators of both diabetes and hypertension.
Dr. Storey told MNT that “[d]iabetes is the most commonly diagnosed disease given the frequency of the illness as well as the classic findings on retina exam, which can include bleeding, leakage of fluid, and areas of poor blood flow.”
Although a firm diagnosis of diabetes can only be made with a blood glucose test, changes in the blood vessels of the retina can give a strong indication that a person may have diabetes. They can then be referred for further testing.
According to the American Academy of Ophthalmology, the signs of diabetic retinopathy can sometimes be detected by eye examination even before a person suspects they may have diabetes.
Once diagnosed, provided the diabetes is well controlled, the person can then minimize the risk of further eye damage, as Dr. Ibrahim explained: “In addition to localized eye therapies such as laser treatment or intravitreal eye injections, improving blood sugar levels by sticking to the proper pharmacological treatment, restricting sugar intake and making necessary lifestyle changes, can result in regression of diabetic retinopathy.”
However, for those with diabetes, the most important eye tests take place after diagnosis, to monitor changes in the eyes and take steps to prevent further damage, as Dr. Howard R. Krauss, surgical neuro-ophthalmologist and director of Pacific Neuroscience Institute’s Eye, Ear & Skull Base Center at Providence Saint John’s Health Center in Santa Monica, CA, noted:
“In most cases, diabetes is diagnosed before changes become evident in the retina, but the retinal examination is a vital part of routine diabetic evaluations, so as to aid in the management of the disease, and to intervene when indicated, with any of a variety of treatments to reduce the risk of blindness from diabetic retinopathy.”
Classic signs of hypertension
Studies have shown that signs of hypertension, or high blood pressure, are found in the eyes of around 10% of the adult, diabetes-free population.
On examination, an eye doctor might see traces of narrowing of arterioles in the retina, arteriovenous nicking, retinal hemorrhages, and, as in diabetic retinopathy, microaneurysms. All these are indicators of hypertensive retinopathy.
“Hypertension also presents with classic signs within the eye. The earliest signs of hypertension are narrowing of the vessels, often referred to as ‘silver wiring’ because of their appearance.”
– Dr. Philip Storey
The good news is that if the hypertension is controlled, the damage can be halted, as Dr. Ibrahim explained.
“Early detection means that appropriate precautions are taken and necessary lifestyle changes are made, such as eating a healthy diet and exercising regularly, in addition to starting the proper medical treatment thereby reducing the risk of heart disease,” she told us.
What the optic nerve can reveal
During a routine eye test, the eye doctor will also examine the optic nerve to look for any abnormalities or changes.
Dr. Ibrahim explained why: “The optic nerve connects the eye to the brain and is therefore an extension of the central nervous system. It is the only part of the brain that can be clearly visualized by examining the back of the eye.”
“Optic nerve swelling or inflammation can be detrimental to vision and color vision, and can diagnose MS, [which is] an autoimmune demyelinating disease of the brain and spinal cord, [as well as] neuroinflammatory disorders such as neuromyelitis optica or brain tumor,” she added.
Vision problems in MS, which tend to flare up then resolve within a few weeks, are usually a result of optic neuritis, an acute inflammatory demyelinating disorder of the optic nerve.
Optic neuritis is the first symptom in up to 20% of people who are subsequently diagnosed with MS, although it can indicate other disorders, or even be the result of a viral infection or vitamin deficiency.
If an optometrist suspects optic neuritis in a routine eye examination, they will refer a person for further testing to confirm the diagnosis and identify the cause.
Signs of Alzheimer’s in the eyes
“Retinal screening of Alzheimer’s disease is an exciting prospect at the forefront of current medical research. The retina […] is made up of multiple layers of specialized neural cells and there is strong evidence that the same changes in the brain can occur in the retina, potentially allowing screening patients for early signs of Alzheimer’s disease.”
– Dr. Hagar Ibrahim
Current methods of diagnosing Alzheimer’s are often lengthy, invasive and expensive, so being able to diagnose the condition from the retina would be a huge advance.
Although this is not yet a disease that can be diagnosed from a routine eye examination, recent research has suggested that doctors could, in the future, diagnose Alzheimer’s through retinal scans.
The new technique, so far tested only in mice, combines the results of two scans to assess the condition of the retina. Those with Alzheimer’s disease have a much rougher retinal surface than those without.
Other research has identified beta-amyloid plaques on the retina as an indication of Alzheimer’s disease, and also in the lens of the eye, both of which can be detected by non-invasive methods.
Dr. Ibrahim explained some of the new developments:
“There are several areas under research. Firstly, looking for the presence of beta-amyloid fragments in the retina, which may be detected by specialist retinal imaging modalities, before symptom onset. […] Secondly, looking at biomarkers detectable on retinal OCT-A images in the form of differences of retinal microvasculature in patients with Alzheimer’s disease and mild cognitive impairment compared to healthy controls.”
Perhaps these findings may lead to easier, earlier diagnosis of Alzheimer’s disease enabling treatment to begin before symptoms become severe.
Get regular eye tests
As well as allowing an optometrist to detect diseases elsewhere in the body, changes in the eyes can tell a physician how a systemic disease is progressing.
So regular eye tests are important, particularly as we get older, as Dr. Benjamin Bert, an ophthalmologist at MemorialCare Orange Coast Medical Center in Fountain Valley, CA, told MNT:
“While eye exams are mostly to check the health of the eyes, they do help to screen for systemic diseases. For adults, if you don’t have any need for glasses or contact lenses, it is still recommended to get an annual exam at least once in your 20s, twice in your 30s, and more regularly after 40. After 40 is when eye-specific ailments can start to become more common — including presbyopia, glaucoma, cataract, and changes to the retina from diabetes or high blood pressure.”
Dr. Krauss reiterated the same advice.
But it is also important to remember that eye examinations are only one tool in monitoring health conditions.
“An examination of the retina often reflects the severity of a disease throughout the body. […] However, patients should not rely on an eye examination to assess how well their systemic disease is controlled,” Dr. Storey cautioned.
“The damage that we see in the eye can take years to occur. Even when a patient’s eye examination is normal, their systemic disease — hypertension or diabetes for example — could be poorly controlled,” he explained.
So, make sure a regular eye test is part of your overall health care, particularly as you get older — it may just detect a condition that you were unaware of, helping you to take control of your health.
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