How Diabetes Can Affect the Eyes

Most people know that diabetes is about insulin abnormalities, whether it’s not producing enough insulin or body’s inability to recognize insulin and use it properly (in type 1 diabetes) or resistance to insulin (in type 2 diabetes).  Quite a few know that the pancreas is involved in this, and are at least vaguely aware that diabetes can result in a host of complications. The connection between the diabetes and those problems, however, is less clear.  How can insulin affect the eyes or the kidneys or the limbs?  It’s not an unreasonable thing to wonder, but in fact the abnormal blood sugar due to diabetes can cause a variety of problems.

Blood is filled with a variety of substances that it sends through the body.  Some of those are electrolytes, a phrase that many are familiar with from Gatorade commercials.  The one that causes diabetic complications in someone with insulin abnormalities is glucose.  It’s a form of sugar, the one that the body breaks down all sugars (simple and complex carbohydrates) into. That sugar is corrosive to blood vessels. In most patients with a working pancreas and functioning insulin levels, the glucose doesn’t stay in the blood long enough to cause serious damage – it’s fed to cells and any extra is eliminated through the kidneys.  Insulin production or response isn’t normal in a diabetic patient, though.  In a type 1 diabetic patient, the beta cells in the pancreas aren’t producing insulin because of an autoimmune reaction, or in some cases the insulin produced is not being recognized by the body. In type 2 diabetes, the beta cells work fine, but a constant presence of sugar makes the cells much less responsive to the insulin they put out.

“When sugar stays in the blood, it will weaken and damage blood vessels”

As a result of the high sugar levels from untreated diabetes, enzymes that control the metabolism of glucose are affected causing premature aging of the endocrine system. As a result, diabetic patients are more prone to cataracts, collagen problems, and other conditions normally associated with aging. When sugar stays in the blood, it will weaken and damage blood vessels nearby. Those vessels are arteries, veins, and capillaries; all three distribute blood cells through the body.  When veins and arteries are damaged, there is impaired blood flow.  That blood flow impairment will affect limbs by cutting off circulation, eventually removing sensation, increasing the chance of systemic infection, and increasing the chance that a limb will have to be amputated.  It will affect the kidneys by damaging the nephrons that filter the blood of the extra electrolytes, eventually causing those nephrons to stop functioning.  And it will affect the eyes.

Eyes don’t have large arteries or veins serving them like the limbs or the kidneys do, but they’re still served through the capillaries by blood.  The scarring present from long term high blood sugar is a problem, but that’s only half the issue. Capillaries are fragile: they can break or rupture much more easily than other larger blood vessels.  Anyone who has had bloodshot eyes has had this.  When the capillaries that aren’t visible rupture, they can bleed more.  The rupture causes damage to the retina in itself and the bleeding can lead to blood clots that block the eye.  Both of those cause the remaining vessels to swell to attempt to cut off the source of the bleeding.  Those combined are the start of diabetic retinopathy.  The true start is laid down by the high blood sugar, but there are no visible symptoms of that until the damage from it is already done.

Understanding how high blood sugar will lead to damage of the blood vessels – even when the diabetic patient feels perfectly normal – is the start of understanding the damage diabetes can do to someone, including diabetic retinopathy.  The first step is to keep blood sugar under control, with diet or a combination of diet and medications (and possibly injections).  Unfortunately, even with proper management of blood sugar, diabetic people usually still have blood sugar spikes and lows more frequently than non-diabetic people.  All diabetic patients should understand the various complications the disease can bring and be screened for the ones that can be diagnosed early on a regular basis.  Some of these steps are basic, like examining the limbs for signs of small wounds to make sure they don’t progress further (which could lead to amputation), and can be done at home.  Some of those screening methods are only to be found in a doctor’s office, like those for kidney abnormalities and retinopathy.  In addition to seeing an endocrinologist regularly diabetic patients should be screened by ophthalmologists and nephrologists.

“By the time there are symptoms of diabetic retinopathy, the damage from it is already done”

The early screening is especially important in the case of diabetic retinopathy, where it can progress to a permanent injury to the eyes before any symptoms show up and result in vision impairment or blindness.  Unlike the legs or arms, eyes can’t be given a once-over every day for small wounds.  This is why early screening is needed and why a professional has to look at the eyes: the eye has to be examined by sensitive instruments.  By the time the symptoms are obvious to the patient, there’s usually permanent damage.  The methods used to treat diabetic retinopathy rely on laser for burning the clots or abnormal blood cells from the eye and injections into the eye that can prevent damage from going further, but can’t reverse the disease.

Moral of the lesson? Diabetes can do a lot of silent damage.  Don’t wait for that to become visible; detect and prevent what you can.


Original article by Annie Keller, with additional contributions from Greg Russell.

Cover image:

[Posted on behalf of Annie Keller]

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