Diabetes mellitus is a chronic disease that impacts millions of people worldwide. While it’s usually well-understood that diabetes impacts the body’s ability to regulate its blood sugar levels, there is much more to it than that.
High blood glucose causes damage to blood vessels supplying oxygen- and nutrient-rich blood to all of the body’s organs and systems.
While having acute (short-term) high blood sugar doesn’t usually cause any lasting damage, chronic high blood sugar from diabetes can cause irreversible damage to these critical blood vessels.
The body counteracts high blood sugar by releasing insulin from the pancreas. Insulin is a hormone that allows the sugar (glucose) in the bloodstream to enter the cells where it’s used for energy. Diabetes results from a lack of insulin, such as in type 1 diabetes or an insulin deficiency associated with type 2 diabetes.
Type 2 diabetes is the most common type of diabetes, whereas type 1 diabetes is an autoimmune disease and is much rarer.
Most diabetes complications result from damage being caused to the blood vessels from chronic high blood glucose. Some common diabetes-related complications include heart disease, kidney disease, nerve damage (neuropathy), and diabetic eye disease, including diabetic retinopathy.
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Diabetes and Eye Health
When blood sugar levels are high, it can cause swelling in the blood vessels in the eye. In the short-term, such as with temporary high blood sugar, this doesn’t cause any significant damage to the eye. However, chronic high blood glucose levels can cause damage to the blood vessels in the eyes and lead to diabetic eye disease.
Changes to the blood vessels in the eyes can begin as early as when someone develops prediabetes. In this condition, blood sugars are higher than usual but not to the point of being diagnosed with diabetes.
With consistent high blood glucose levels, the eye’s small blood vessels may swell and leak fluid into the eye. New blood vessels that are weaker than they should be can also begin to grow in the eye.
These weak and abnormal blood vessels can bleed into the eye and cause scarring, or the pressure in the high might grow to dangerously high levels. When this happens, vision is impacted, and it can even lead to blindness. In fact, diabetes is the leading cause of blindness in people aged 20-74.
There are four main types of diabetic eye disease, including:
- Diabetic retinopathy: The retina is the inner lining in the back of the eye that senses light and allows us to see. Diabetic retinopathy is when the blood vessels supplying blood to the retina become damaged. When this occurs, the blood vessels can weaken, bulge, and leak into the retina. This early stage of diabetic retinopathy is called nonproliferative diabetic retinopathy.
If the process continues to worsen, some of the retina’s blood vessels will close off, which causes new blood vessels to grow or proliferate. These new blood vessels increase on the surface of the retina, which causes serious vision changes. This is called proliferative retinopathy, and the body attempts to save the retina. Proliferative retinopathy causes scarring on the retina, which can lead to blindness.
- Retinal detachment occurs when the retina pulls away from the blood vessels supplying oxygen and nutrients to the retina. Retinal detachment is painless but can lead to permanent vision loss if it’s not treated and it advances. Symptoms of retinal detachment include the sudden appearance of “floaters” in the vision, flashes of light, blurred vision, reduced peripheral (side) vision, and a curtain-like shadow over the field of vision. It’s estimated that almost one-third of adults over the age of 40 with diabetes have diabetic retinopathy. Its prevalence is even higher in African Americans and Mexican Americans.
- Diabetic macular edema: The part of the retina that allows us to read, drive and recognize faces is called the macula. With diabetic eye disease, the macula can swell and thicken, which impairs someone’s sharp vision. Partial or total vision loss can occur due to diabetic macular edema and typically impacts people who have signs of diabetic retinopathy.
- Glaucoma: Glaucoma is the name for a group of eye diseases that causes damage to the optic nerve. The optic nerve is a bundle of nerves that connects the eye to the brain. While there are certain risk factors for glaucoma, such as being over age 60, being either African American or Hispanic/Latino and over the age of 45, and having a family history of glaucoma, diabetes doubles the likelihood of having glaucoma. Glaucoma can lead to vision loss and blindness if treatment is delayed.
- Cataracts: The lens of the eye is a clear structure that allows for sharp vision, such as when reading. The lenses of the eye can become clouded with age, leading to less sharp vision. People with diabetes are more likely to develop cataracts at earlier ages compared to non-diabetics. This might be due to high blood sugar causing deposits on the lens of the eye.
Risk factors & Symptoms
Diabetic eye disease is estimated to impact over 25% of people with type 2 diabetes and over half of people with type 1 diabetes. Just because someone has diabetes doesn’t mean that they will develop eye problems. Keeping blood sugar levels well-controlled is the best way to prevent complications such as diabetic eye disease.
Some of the risk factors for developing diabetic eye disease include:
- Having diabetes for a long time
- Poor blood sugar control
- High blood pressure
- High cholesterol
- Tobacco use
- Being African-American, Hispanic, or Native American
Some of the symptoms of diabetic eye problems include:
- Spots or dark strings floating in your vision (also called “floaters”)
- Blurred vision
- Fluctuating vision
- Impaired color vision
- Dark or empty areas in your vision
- Vision loss
What’s involved in a diabetic eye exam?
During a diabetic eye exam, the eye doctor will gather information about the patient’s medical history, including blood sugar control, blood pressure, medication use, etc. They’ll also look at the retina with a tool called an ophthalmoscope. Some aspects of retinopathy cannot be viewed during a basic eye exam and require a dilated eye exam to better view the retina.
During a dilated eye exam, the optometrist or ophthalmologist will put eye drops in the eye that make the retina dilate or increase in size. They will then look at the retina with a special light called a slit lamp. An optometrist isn’t a medical doctor but is qualified to perform eye exams and prescribe corrective lenses.
Compared to an optometrist, an ophthalmologist is more qualified to treat complex diseases of the eye, such as diabetic retinopathy. They also perform surgeries on the eye. Ophthalmologists have a medical degree and have completed a residency in ophthalmology. Either one of these healthcare professionals can perform a diabetic eye exam. However, people with complex eye issues will likely be referred to an ophthalmologist.
It’s recommended for people with type 1 diabetes to receive a dilated eye exam within 5 years of diagnosis and then yearly after that. People with type 2 diabetes should receive a dilated eye exam once they are diagnosed and then yearly after that. Some doctors may suggest having an eye exam every 2-3 years after a normal exam for people with type 2 diabetes. You should always check with your healthcare provider to determine how often to go in for a comprehensive eye exam.
In order to look for changes in the structure and function of the retina’s blood vessels, a test called fluorescein angiography may be used. Fluorescein angiography involves injecting a fluorescent yellow dye into a vein and then photographing the retina once the dye reaches and outlines the retina’s blood vessels.
During a comprehensive eye exam, the eye doctor will also check for glaucoma and cataracts. The glaucoma test involves tonometry, which measures the pressure within the eye. Eye pressure is measured by a machine that delivers a small puff of air to the eye. Most cases of glaucoma are diagnosed when the intraocular pressure exceeds 20 mm Hg.
During an eye exam, the patient will receive a series of vision tests to check visual acuity, reported in terms of 20/15, 20/20, 20/40, etc. These numbers signify how well someone can see the letters or objects at a certain distance. For instance, 20/15 vision means a person can read at 20 feet from the chart what most “normal” people can see at 15 feet from the chart. 20/20 vision is often considered “perfect,” when in fact, 20/15 or 20/10 vision signifies even better vision than 20/20.
The importance of diabetic eye exams
Diabetic eye exams are important to screen for eye problems early. When diabetic eye disease is caught early on, there is a better chance of treating it and minimizing the damage to the person’s vision. There are treatments and surgeries for conditions like cataracts and glaucoma, so having these conditions doesn’t necessarily mean vision will be lost.
People with diabetes are more likely to suffer from high blood pressure. High blood pressure is another risk factor for developing eye disease since increased eye pressure from high blood pressure can lead to vision problems.
Even if someone isn’t experiencing a change in vision or vision loss, it’s important to keep up with regular eye exams. Changes to the retina can be detected before the person might have symptoms of eye disease. If someone waits until they have symptoms of eye disease, it may be too late to effectively treat, and vision loss may occur.
The ultimate complication of diabetic eye disease is the complete loss of vision resulting in blindness. In the Wisconsin Epidemiologic Study of Diabetic Retinopathy (WESDR), 3.6% of patients with younger-onset diabetes (type 1 diabetes) and 1.6% of older-onset patients (type 2 diabetes) were legally blind.
Diabetes causes damage to the body’s blood vessels, leading to diabetes complications such as diabetic eye disease. There are four main types of diabetic eye disease: diabetic retinopathy, diabetic macular edema, glaucoma, and cataracts. Each of these types of eye disease can lead to vision loss if not diagnosed early.
Some signs of diabetic eye disease include a change in vision, blurry vision, increased “floaters” in the field of vision, and loss of peripheral vision.
It’s important that all people with diabetes receive a comprehensive eye exam yearly to screen for eye disease. A dilated eye exam allows the eye doctor to better view the retina to check for signs of diabetic retinopathy. It’s usually recommended that people receive a dilated eye exam every year, though they might be recommended every 2-3 years if results are normal.
An eye exam will involve:
- Checking visual acuity.
- Viewing the retina and its blood vessels for changes.
- Measuring the pressure in the eye and more.
The best way to prevent diabetic eye disease is to keep blood sugar levels well controlled and keep up with preventative healthcare visits, including regular eye exams.